- Dpt. Fisica de la Materia Condensada
Facultad de Ciencia y Tecnologia
Universidad del Pais Vasco (UPV/EHU)
Aptdo 644, 48080 Bilbao
SPAIN
An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical... more
An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical micro- and nanocavities are promising for a wide range of applications. They can be created within microwires and nanowires via distributed Bragg reflectors (DBR), i.e., periodic patterns of the refractive index in dielectric materials, acting as tunable mirrors. In this work, the effect of temperature on the anisotropic refractive index of β-Ga2O3 n(λ,T) was analyzed with ellipsometry in a bulk crystal, and temperature-dependent dispersion relations were obtained, with them being fitted to Sellmeier formalism in the visible range. Micro-photoluminescence (μ-PL) spectroscopy of microcavities that developed within Cr-doped β-Ga2O3 nanowires shows the characteristic thermal shift of red–infrared Fabry–Perot optical resonances when excited with differe...
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A novel Shape Memory Alloy (SMA) has been developed as an alternative to currently available alloys. The material and related processes are fully European. This material, called SMARQ, shows higher working range of temperatures with... more
A novel Shape Memory Alloy (SMA) has been developed as an alternative to currently available alloys. The material and related processes are fully European. This material, called SMARQ, shows higher working range of temperatures with respect to the SMA materials used until now. This temperature restriction is one of the most critical limitations of the current SMA devices for their use in space and other applications. This new alloy has been proposed for its use in actuators for space mechanisms. A full characterization test campaign has been completed in order to obtain the main material properties and check its suitability as active material in space actuators. The test campaign includes: strength characterization, temperature characterization, electrical activation at different environment temperatures in the range from -70ºC to +125ºC, lifetime tests and vacuum tests at ambient temperature. Results of this characterization test campaign will be presented in this work. As part of ...
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Shape memory alloys (SMAs) are functional materials that are being applied in practically all industries, from aerospace to biomedical sectors, and at present the scientific and technologic communities are looking to gain the advantages... more
Shape memory alloys (SMAs) are functional materials that are being applied in practically all industries, from aerospace to biomedical sectors, and at present the scientific and technologic communities are looking to gain the advantages offered by the new processing technologies of additive manufacturing (AM). However, the use of AM to produce functional materials, like SMAs, constitutes a real challenge due to the particularly well controlled microstructure required to exhibit the functional property of shape memory. In the present work, the design of the complete AM processing route, from powder atomization to laser powder bed fusion for AM and hot isostatic pressing (HIP), is approached for Cu–Al–Ni SMAs. The microstructure of the different processing states is characterized in relationship with the processing parameters. The thermal martensitic transformation, responsible for the functional properties, is analyzed in a comparative way for each one of the different processed samp...
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Shape Memory Alloys exhibit a superelastic stress-induced phase transformation with a high displacement actuation, which are promising for applications in Micro Electromechanical Systems (MEMS). Previous works demonstrate a completely... more
Shape Memory Alloys exhibit a superelastic stress-induced phase transformation with a high displacement actuation, which are promising for applications in Micro Electromechanical Systems (MEMS). Previous works demonstrate a completely reversible and reproducible behaviour at nanoscale [1,2], even for thousands of cycles [3]. However, some fundamental aspects at nanoscale remain unclear, in particular whether the critical stress for superelasticity exhibits a sizeeffect similar to that observed in confined plasticity. Our results provide the evidence of a strong size-effect on the critical stress that induce such phase transformation [4]. This has been observed in pillars, milled by FIB in single crystal slides from Cu-Al-Ni and other SMA, from 2 μm to 260 nm in diameter. The critical stress for superelasticity has been measured by nano-compression tests. A power-law size dependence of n=-2 has been determined for the superelasticity at nanoscale. Our observations are explained throu...
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Research Interests: Materials Science, Microstructure, Behavior, Stress, Hysteresis, and 15 moreShape Memory Alloys, Differential scanning calorimetry, Enthalpy, Nucleation, Temperature, Diffraction, Thermal, Shape Memory Alloy, Metals, Phase, Grains, Nickel Titanium, Martensitic Transformation, Thermal Properties, and Crystallite
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ABSTRACTNowadays, aeronautic and aerospace are the more demanding sectors for shape memory alloys (SMA) after the bio-medical one. In particular the interest has been recently focused on very high temperature SMA, which would be able of... more
ABSTRACTNowadays, aeronautic and aerospace are the more demanding sectors for shape memory alloys (SMA) after the bio-medical one. In particular the interest has been recently focused on very high temperature SMA, which would be able of working as sensors and actuators in the hot areas of the engines and exaust devices.In the present work we undertook a study of the Ru-Nb SMA Intermetallics, which undergo two succesive martensitic transformations around 1050 K and 1180 K respectively, depending on composition. This study has been focused on measurements of internal friction spectra and dynamic modulus variation up to 1700 K, which have been carried out in a sub-resonant torsion mechanical spectrometer.The internal friction and dynamic modulus have been studied as a function of the heating-cooling rate and the frequency in order to compare experimental behaviour with theoretical models for martensitic transformations. In addition to the internal friction peaks linked to both martensi...
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Shape memory alloys undergo reversible transformations between two distinct phases in response to changes in temperature or applied stress. The creation and motion of the internal interfaces between these phases during such... more
Shape memory alloys undergo reversible transformations between two distinct phases in response to changes in temperature or applied stress. The creation and motion of the internal interfaces between these phases during such transformations dissipates energy, making these alloys effective mechanical damping materials. Although it has been shown that reversible phase transformations can occur in nanoscale volumes, it is not known whether these transformations have a sample size dependence. Here, we demonstrate that the two phases responsible for shape memory in Cu-Al-Ni alloys are more stable in nanoscale pillars than they are in the bulk. As a result, the pillars show a damping figure of merit that is substantially higher than any previously reported value for a bulk material, making them attractive for damping applications in nanoscale and microscale devices.
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ABSTRACT Superelastic behavior at nano-scale has been studied along cycling in Cu-Al-Ni shape memory alloy micropillars. Arrays of square micropillars were produced by focused ion beam milling, on slides of [001] oriented Cu-Al-Ni single... more
ABSTRACT Superelastic behavior at nano-scale has been studied along cycling in Cu-Al-Ni shape memory alloy micropillars. Arrays of square micropillars were produced by focused ion beam milling, on slides of [001] oriented Cu-Al-Ni single crystals. Superelastic behavior of micropillars, due to the stress-induced martensitic transformation, has been studied by nano-compression tests during thousand cycles, and its evolution has been followed along cycling. Each pillar has undergone more than thousand cycles without any detrimental evolution. Moreover, we demonstrate that after thousand cycles they exhibit a perfectly reproducible and completely recoverable superelastic behavior.
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ABSTRACT The martensitic transformations in ultra-high temperature Ru-50Nb shape memory alloys have been studied by internal friction and dynamic modulus measurements. Two successive transformations from the high temperature cubic β phase... more
ABSTRACT The martensitic transformations in ultra-high temperature Ru-50Nb shape memory alloys have been studied by internal friction and dynamic modulus measurements. Two successive transformations from the high temperature cubic β phase to a tetragonal β′ martensite and then to another monoclinic β″ martensite have been found. Both transformations exhibit a sharp internal friction peak and a clear softening of the dynamic modulus, being a signature of the thermo-elastic martensitic transformations. In addition, a pseudo relaxation peak strongly dependent on time has been found and analyzed, concluding that it is linked to a pinning effect of martensite interfaces by point defects.
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ABSTRACT Stress-induced martensite nucleation and further growing, in Cu–Al–Ni shape memory alloys, have been studied during in situ superelastic tests in the transmission electron microscope. Two kinds of martensite, β3′ and γ3′, are... more
ABSTRACT Stress-induced martensite nucleation and further growing, in Cu–Al–Ni shape memory alloys, have been studied during in situ superelastic tests in the transmission electron microscope. Two kinds of martensite, β3′ and γ3′, are induced and can coexist under stress, both exhibiting in a high density of stacking faults. The interface plane and the orientation relationships between the different variants of such martensites have been determined, and the atomic configurations of the lattices across the interface have been described. Finally, in light of the results, selection rules for the stress-induced promoted martensites at the nano-scale have been established, being determined by the shear direction and the basal plane of the martensite lattice.
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ABSTRACT Among active materials, shape memory alloys are well recognized for their work output density. Because of that, these alloys have attracted much attention to be used in micro/nano electromechanical systems. In the present work,... more
ABSTRACT Among active materials, shape memory alloys are well recognized for their work output density. Because of that, these alloys have attracted much attention to be used in micro/nano electromechanical systems. In the present work, the electron beam evaporation technique has been used to growth, by a multilayer method, two shape memory alloy thin films with different Cu-Al-Ni composition. Multilayers have been further thermally treated to produce the alloys by solid solution diffusion. The produced multilayers have been characterized and the presence of the martensite phase in the obtained thin films was studied. Furthermore, the influence of two different coatings onto the Si substrates, namely Si/SiO2 and Si/Si3N4, was investigated. Mechanically stable, not detaching from the substrates, Cu-Al-Ni shape memory alloy thin films, about 1 micrometre thick, showing a martensitic transformation have been produced.
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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with... more
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights Abstract An advanced intermetallic c-TiAl-based alloy containing Nb and Mo has been studied to understand the microscopic mechanisms taking place during thermal treatments carried out to adjust a fine, nearly lamellar microstructure. The evolution of the microstructure has been characterized by high-energy X-ray diffraction and electron microscopy, while the atomistic mechanisms of defect mobility have been studied through internal friction and dynamic modulus measurements. An internal friction relaxation peak has been observed at about 1050 K (for 1 Hz) in the initial oversaturated a 2-Ti 3 Al phase, whose intensity strongly decreases after precipitation of the c-TiAl laths. The activation parameters of this relaxation have been measured, H act = 3.1 ± 0.05 eV, s 0 = 8.3 Â 10 À17 s and b = 1.3, and the relaxation is attributed to a point defect mechanism taking place inside the supersaturated a 2-Ti 3 Al phase. A new Zener-like atomistic model based on stress-induced reorientation of Al–V Ti –Al dipoles has been developed to explain the observed relaxation, resolving the controversy concerning the relaxation peak at 1050 K present in many c-TiAl-based alloys. Precipitation of the c-lamellae has also been considered as being responsible for the dynamic modulus hardening and, additionally, for another contribution to the internal friction at higher temperature than the described relaxation. Finally, the theoretical Debye equations as a function of temperature, for both internal friction and dynamic modulus, have been applied, using the measured activation parameters, to perform a deconvolution of the relaxation and precipitation contributions. The obtained results agree well with the experimental ones at different frequencies, allowing a global interpretation of the involved atomic processes.
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The thermal behaviour of ZnO nanotubes partially filled with Sn cores, containing also Sn nanoclusters and nanovoids, has been investigated by in-situ heating treatments in a transmission electron microscope (TEM). The size effect on... more
The thermal behaviour of ZnO nanotubes partially filled with Sn cores, containing also Sn nanoclusters
and nanovoids, has been investigated by in-situ heating treatments in a transmission electron microscope
(TEM). The size effect on the melting temperature of Sn nanoclusters and nanorods, and diffusion
of voids along the nanotube axis have been studied by directly recording the TEM images during heating
treatments. Melting temperatures of 163 C and 213C were found for a 10 nm diameter particle and a
30 nm diameter Sn core respectively. Different diffusion processes in the Sn-ZnO core/shell structure at
640 C are described.
and nanovoids, has been investigated by in-situ heating treatments in a transmission electron microscope
(TEM). The size effect on the melting temperature of Sn nanoclusters and nanorods, and diffusion
of voids along the nanotube axis have been studied by directly recording the TEM images during heating
treatments. Melting temperatures of 163 C and 213C were found for a 10 nm diameter particle and a
30 nm diameter Sn core respectively. Different diffusion processes in the Sn-ZnO core/shell structure at
640 C are described.
Shape memory alloys are one of the most important families of functional materials due to superelasticity and shape memory properties. In particular Cu-Al-Ni alloys exhibit these properties at nanoscale, becoming potentially useful to... more
Shape memory alloys are one of the most important families of functional
materials due to superelasticity and shape memory properties. In particular
Cu-Al-Ni alloys exhibit these properties at nanoscale, becoming potentially
useful to design new smart MEMS. In this work, an anomalous behavior
observed during nano-compression superelastic tests on Cu-Al-Ni shape
memory alloy micro pillars is reported. The study is approached by nanocompression
tests on micro and nano pillars milled by focused ion beam. The
anomalous behavior on the superelastic effect is manifested by a sudden
stabilization of the stress-induced martensite, which does not undergo the
reverse transformation. A transition, from superelastic to pseudoelastictwinning
behavior, takes place during the nano-compression tests, and is
evaluated through the load-depth curves and quantified by the mechanical
damping coefficient η, which undergoes a sharp change from ultra-high
damping, η>0.1, down to η0.01. The stabilization of the martensite occurs
under two different experimental conditions, along cycling and by applying a
very high stress during superelastic tests. In both cases, a further recovery of
the initial superelastic behavior is registered. The mechanisms responsible for
the observed stabilization and recovery are discussed, together with the
implications and further requirements for technological applications in MEMS.
materials due to superelasticity and shape memory properties. In particular
Cu-Al-Ni alloys exhibit these properties at nanoscale, becoming potentially
useful to design new smart MEMS. In this work, an anomalous behavior
observed during nano-compression superelastic tests on Cu-Al-Ni shape
memory alloy micro pillars is reported. The study is approached by nanocompression
tests on micro and nano pillars milled by focused ion beam. The
anomalous behavior on the superelastic effect is manifested by a sudden
stabilization of the stress-induced martensite, which does not undergo the
reverse transformation. A transition, from superelastic to pseudoelastictwinning
behavior, takes place during the nano-compression tests, and is
evaluated through the load-depth curves and quantified by the mechanical
damping coefficient η, which undergoes a sharp change from ultra-high
damping, η>0.1, down to η0.01. The stabilization of the martensite occurs
under two different experimental conditions, along cycling and by applying a
very high stress during superelastic tests. In both cases, a further recovery of
the initial superelastic behavior is registered. The mechanisms responsible for
the observed stabilization and recovery are discussed, together with the
implications and further requirements for technological applications in MEMS.
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Shape-memory alloys capable of a superelastic stress-induced phase transformation and a high displacement actuation have promise for applications in micro-electromechanical systems for wearable healthcare and flexible electronic... more
Shape-memory alloys capable of a superelastic stress-induced phase transformation and a high displacement actuation have promise for applications in micro-electromechanical systems for wearable healthcare and flexible electronic technologies. However, some of the fundamental aspects of their nanoscale behaviour remain unclear, including the question of whether the critical stress for the stress-induced martensitic transformation exhibits a size effect similar to that observed in confined plasticity. Here we provide evidence of a strong size effect on the critical stress that induces such a transformation with a threefold increase in the trigger stress in pillars milled on [001] L21 single crystals from a Cu-Al-Ni shape-memory alloy from 2 μm to 260 nm in diameter. A power-law size dependence of n = -2 is observed for the nanoscale superelasticity. Our observation is supported by the atomic lattice shearing and an elastic model for homogeneous martensite nucleation.
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Page 1. Materials Science Forum Vols. 366-368 (2001) pp 32-73 © (2001) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF. 366-368.32 1.2 Mechanical Spectroscopy /. San Juan 1.2.1 Introduction to ...
ABSTRACT A novel shape memory alloy (SMA) has been developed as an alternative to currently available alloys. This alloy, commercially known by its proprietary brand SMARQ, shows a higher working range of temperatures with respect to the... more
ABSTRACT A novel shape memory alloy (SMA) has been developed as an alternative to currently available alloys. This alloy, commercially known by its proprietary brand SMARQ, shows a higher working range of temperatures with respect to the SMA materials used until now in actuators, limited to environment temperatures below 90 A degrees C. SMARQ is a high temperature SMA (HTSMA) based on a fully European material technology and production processes, which allows the manufacture of high quality products, with tuneable transformation temperatures up to 200 A degrees C. Both, material and production processes have been evaluated for its use in space applications. A full characterization test campaign has been completed in order to obtain the material properties and check its suitability to be used as active material in space actuators. In order to perform the functional characterization of the material, it has been considered as the key element of a basic SMA actuator, consisting in the SMA wire and the mechanical and electrical interfaces. The functional tests presented in this work have been focused on the actuator behavior when heated by means of an electrical current. Alloy composition has been adjusted in order to match a transition temperature (As) of +145 A degrees C, which satisfies the application requirements of operating temperatures in the range of -70 and +125 A degrees C. Details of the tests and results of the characterization test campaign, focused in the material unique properties for their use in actuators, will be presented in this work. Some application examples in the field of space mechanisms and actuators, currently under development, will be summarized as part of this work, demonstrating the technology suitability as active material for space actuators.
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Stable phase precipitation produces deleterious effects in the characteristics of the martensitic transformation in shape memory alloys. In particular, the g1 phase appears during heating as a primary precipitation previous to the... more
Stable phase precipitation produces deleterious effects in the characteristics of the martensitic transformation in shape memory
alloys. In particular, the g1 phase appears during heating as a primary precipitation previous to the eutectic reaction in Cu–Al–Ni
alloys. Nevertheless the crystallographic structure of this g1 phase in Cu–Al–Ni alloys is not well known. Neutron Powder Diffraction
measurements have been performed at 546 C in a Cu–27.4 Al–3.6 Ni at.% alloy where two eutectic phases a and g1 have been
identified. Rietveld analysis allows determining the positions and the site occupancy of the different atoms in the g1 phase.
alloys. In particular, the g1 phase appears during heating as a primary precipitation previous to the eutectic reaction in Cu–Al–Ni
alloys. Nevertheless the crystallographic structure of this g1 phase in Cu–Al–Ni alloys is not well known. Neutron Powder Diffraction
measurements have been performed at 546 C in a Cu–27.4 Al–3.6 Ni at.% alloy where two eutectic phases a and g1 have been
identified. Rietveld analysis allows determining the positions and the site occupancy of the different atoms in the g1 phase.
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In the last decades, issues on absorption of vibration energy have attracted much attention in several technological sectors like vibration isolation in high-precision electronics, building protection in civil engineering, etc.. In the... more
In the last decades, issues on absorption of vibration energy have attracted much attention in several technological sectors like vibration isolation in high-precision electronics, building protection in civil engineering, etc.. In the past, mainly polymers were used as high-damping materials, but the increasingly demanding working conditions (e.g. high service temperature) have encouraged the scientific community to look for alternative materials. High-damping metallic materials and, in particular, metal matrix composites were proposed as a feasible solution. Among them, shape memory alloys (SMA) intrinsically show very high damping properties, thanks to dissipative movements of the interfaces generated during their characteristic martensitic transformation, which have already found some practical damping applications. Taking advantage of both the high-damping capacity of Cu-Al-Ni SMAs and the flexibility of composite production, very high-damping metal matrix composites were devel...
Damping in structural applications require not only a high damping coefficient η but also a stiff behaviour in order to avoid the deformation of the structure, so the optimization of structural damping require a high merit index η·E.... more
Damping in structural applications require not only a high damping coefficient η but also a stiff behaviour in order to avoid the deformation of the structure, so the optimization of structural damping require a high merit index η·E. Using a patented technology of ultra-high damping composite materials based on SMA, we have developed some prototypes of dampers which exhibit both stiffness and high damping coefficient. In this work we give a description of such dampers, as well as their characteristics and performances. We analyse some potential applications in several industrial sectors. Besides, these new dampers offer excellent performances at low frequencies, where the dynamic damping systems start to loose their good characteristics, and they also show a good potential to work in series with such devices to extend their performance at low frequencies.
In the last years absorption of vibration energy by mechanical damping have attracted much attention in several fields like vibration reduction in aircraft and machinery industries, nano-scale vibration isolations in electronic industry,... more
In the last years absorption of vibration energy by mechanical damping have attracted much attention in several fields like vibration reduction in aircraft and machinery industries, nano-scale vibration isolations in electronic industry, vibration damping in civil engineering, etc. For structural applications, materials that combine a high damping capacity and high stiffness at moderate temperatures are required, but unfortunately this combination is not frequent. Usually, the most used high-damping materials are based on polymers due to their viscoelastic behaviour. However, polymeric materials typically show a low elastic modulus and are not stable at relatively low temperatures (≈ 323 K). Therefore, alternate materials for damping applications are needed. Metallic materials, which originally exhibit better mechanical properties (higher modulus and thermal stability) than polymers, with similar damping properties were proposed to replace polymeric ones. In particular, shape memory...
@font-face { "Times"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; ""; }div.Section1 { page: Section1; } Now a day, high damping materials have attracted the scientific and... more
@font-face { "Times"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; ""; }div.Section1 { page: Section1; } Now a day, high damping materials have attracted the scientific and technological interest, because of their useful applications. Indeed, the use of high damping materials may allow to decrease the acoustic pollution, improve the speed and precision of the tools machines, increase the life of the aeronautical components and to protect buildings against earthquake, for instance. In our laboratory, we have developed a new kind of metal matrix composites, specifically designed to exhibit an ultra-high-damping behavior. These composites are based on a high percentage pre-form of powders of Cu-Al-Ni shape memory alloys (SMA), infiltrated by a soft metallic matrix. The damping properties have been measured by mechanical spectroscopy between 150 K and 400 K as a function of temperature and frequency. Finally, we discuss the o...
Mechanical vibration isolation in several industrial sectors such as electronic, aeronautic, transport, for instance, is necessary in order to improve the quality in new engineering applications and reduce the environment acoustic... more
Mechanical vibration isolation in several industrial sectors such as electronic, aeronautic, transport, for instance, is necessary in order to improve the quality in new engineering applications and reduce the environment acoustic pollution. Shape memory alloys (SMA) exhibit high damping capacity as well as good mechanical properties in a wide temperature range and can be used as passive dampers to replace the traditionally used polymeric materials, which present poor stiffness and are not stable enough for some structural applications even at relative low temperatures. In this work a new kind of metal matrix composite, based on Cu-Al-Ni SMA powders, has been developed. The damping capacity of these composites has been studied by mechanical spectroscopy as a function of temperature, frequency and strain amplitude. The influence of thermal treatments on the thermo-elastic martensitic transformation as well as on the relative contribution from SMA particles and matrices, have been ana...
ABSTRACTShape Memory Alloys (SMA) undergo reversible martensitic transformation in response to changes in temperature or applied stress, exhibiting specific properties of superelasticity and shape memory. At present there is a high... more
ABSTRACTShape Memory Alloys (SMA) undergo reversible martensitic transformation in response to changes in temperature or applied stress, exhibiting specific properties of superelasticity and shape memory. At present there is a high scientific and technological interest to develop these properties at small scale, to apply SMA as sensors and actuators in MEMS technologies. In order to study the thermo-mechanical properties of SMA at micro and nano scale, instrumented nano indentation is being widely used for nano compression tests. By using this technique, superelasticity and shape memory at the nano-scale has been demonstrated in micro and nano pillars of Cu-Al-Ni SMA. However the martensitic transformation seems to exhibit a different behavior at small scale than in bulk materials and a size effect on superelasticity has been recently reported. In the present work we will overview the thermo-mechanical properties of Cu-Al-Ni SMA at the nano-scale, with special emphasis on size effec...
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ABSTRACT Until now TiAl alloys have been produced using a variety of processing methods including forging, extrusion, casting, etc. One important problem is the variation in mechanical properties caused by the segregation in the... more
ABSTRACT Until now TiAl alloys have been produced using a variety of processing methods including forging, extrusion, casting, etc. One important problem is the variation in mechanical properties caused by the segregation in the composition. In order to improve these segregations, powder metallurgy is an interesting alternative for the processing of TiAl alloys. However, some drawbacks of PM have limited the practical application of TiAl alloys such as the costs of the pre-alloyed raw materials, the use of expensive processing methods like HIP, etc. This work presents the activities performed at Tecnalia in the development of novel cost effective PM processing routes. Processes like Spark Plasma Sintering and Combustion Synthesis will be presented. Microstructures, crystallographic phases, chemical analysis and mechanical properties (tensile and creep) of the different processing routes will be detailed. Main advantages of these methods are the short processing time and the possibility of using elemental powders.
This is an Application Note (MET07ANr1.f) presented at the Web-site of Hysitron, describing the possibilities of the Triboindenter equipment, based on our works on pillar nano-compression tests.
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ABSTRACT A novel shape memory alloy (SMA) has been developed as an alternative to currently available alloys. This alloy, commercially known by its proprietary brand SMARQ, shows a higher working range of temperatures with respect to the... more
ABSTRACT A novel shape memory alloy (SMA) has been developed as an alternative to currently available alloys. This alloy, commercially known by its proprietary brand SMARQ, shows a higher working range of temperatures with respect to the SMA materials used until now in actuators, limited to environment temperatures below 90 A degrees C. SMARQ is a high temperature SMA (HTSMA) based on a fully European material technology and production processes, which allows the manufacture of high quality products, with tuneable transformation temperatures up to 200 A degrees C. Both, material and production processes have been evaluated for its use in space applications. A full characterization test campaign has been completed in order to obtain the material properties and check its suitability to be used as active material in space actuators. In order to perform the functional characterization of the material, it has been considered as the key element of a basic SMA actuator, consisting in the SMA wire and the mechanical and electrical interfaces. The functional tests presented in this work have been focused on the actuator behavior when heated by means of an electrical current. Alloy composition has been adjusted in order to match a transition temperature (As) of +145 A degrees C, which satisfies the application requirements of operating temperatures in the range of -70 and +125 A degrees C. Details of the tests and results of the characterization test campaign, focused in the material unique properties for their use in actuators, will be presented in this work. Some application examples in the field of space mechanisms and actuators, currently under development, will be summarized as part of this work, demonstrating the technology suitability as active material for space actuators.
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Research Interests: Dislocations and Iron
Hydrogen Snoek-Koster relaxation is generally attributed to the interaction of dislocations with hydrogen. In the case of iron, two components appear (SK1 around 120 K and SK2 around 160 K at 1 Hz). There is some disagreement about the... more
Hydrogen Snoek-Koster relaxation is generally attributed to the interaction of dislocations with hydrogen. In the case of iron, two components appear (SK1 around 120 K and SK2 around 160 K at 1 Hz). There is some disagreement about the interpretation of the two components of the SK(H) relaxation and the validity of the proposed models. In an attempt to resolve this, the authors make a comparison of the experimental features of SK(H) in iron with those predicted by the proposed models. A new analysis of the SK(H) relaxation is then proposed. This analysis is based on the kink pair formation on non-screw dislocations controlled by the hydrogen diffusion of atoms or clusters. It allows the authors to explain the complementarity between the SK(H) relaxation and the alpha -peak, the dependence of the SK(H) relaxation strength on the hydrogen concentration and the degree of deformation, and the activation parameters of the relaxation.
Research Interests: Dislocations and Iron
This paper aims to determine mechanisms that lie at the origin of internal friction relaxations P, and Pi that have been observed in high purity aluminium (99.9999%). Thus we have studied these relaxation behaviours in relation to... more
This paper aims to determine mechanisms that lie at the origin of internal friction relaxations
P, and Pi that have been observed in high purity aluminium (99.9999%). Thus we have studied these
relaxation behaviours in relation to different experimental conditions (e.g. thermomechanical treatment,
applied stress, either oscillation stress urn, or bias stress o, and frequency). The samples have suffered
various thermomechanical treatments (rolling, annealing and creep) carried out at different temperatures.
Their corresponding microstructures have been analyscd using TEM. We have been able to observe a close
relation between internal friction results and the microstructure. In particular we can say that the presence
of relaxations P, and P; is associated with a tangle dislocation microstructure, whereas its disappearance
after a creep test is associated with the reorganization of the dislocations in polygonization subboundaries.
This, together with the results obtained in internal friction, has allowed us to determine the mechanism
that controls relaxations P, and Pi, which will be presented in part II of this paper.
P, and Pi that have been observed in high purity aluminium (99.9999%). Thus we have studied these
relaxation behaviours in relation to different experimental conditions (e.g. thermomechanical treatment,
applied stress, either oscillation stress urn, or bias stress o, and frequency). The samples have suffered
various thermomechanical treatments (rolling, annealing and creep) carried out at different temperatures.
Their corresponding microstructures have been analyscd using TEM. We have been able to observe a close
relation between internal friction results and the microstructure. In particular we can say that the presence
of relaxations P, and P; is associated with a tangle dislocation microstructure, whereas its disappearance
after a creep test is associated with the reorganization of the dislocations in polygonization subboundaries.
This, together with the results obtained in internal friction, has allowed us to determine the mechanism
that controls relaxations P, and Pi, which will be presented in part II of this paper.
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ABSTRACT
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ABSTRACT The phase transformation and nanoindentation response as a function of crystallinity of NiTi thin films were assessed. A phase change was detectable in samples with 1% crystallization. Measured mechanical properties indicate that... more
ABSTRACT The phase transformation and nanoindentation response as a function of crystallinity of NiTi thin films were assessed. A phase change was detectable in samples with 1% crystallization. Measured mechanical properties indicate that the films soften with crystallization. Films partway through crystallization presented a bimodal response: crystalline regions had moduli similar to fully crystallized films; and amorphous regions had larger moduli (larger than as-deposited amorphous films) attributable to structural relaxation. A modified Voigt model describes the evolution of the modulus in crystallizing films.
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We have developed a new kind of Metal Matrix Composites based on Cu-Al-Ni shape memory alloys, imbibed in a metallic matrix, specifically designed for showing very high damping coefficient, with the characteristic modulus of the... more
We have developed a new kind of Metal Matrix Composites based on Cu-Al-Ni shape memory
alloys, imbibed in a metallic matrix, specifically designed for showing very high damping
coefficient, with the characteristic modulus of the metallic materials.
In the present work we present the damping behavior of such metal matrix composites, has been
studied by Mechanical Spectroscopy, as a function of temperature, between 150 K and 400 K,
and for different frequencies, between 3x10-3 and 3 Hz. These results are very promising,
because the internal friction spectra show a very high maximum linked to the thermo elastic
martensitic transformation, as well as a high damping background, in a very broad range in
temperature. Besides, the temperature of the maximum of damping can be controlled, in order to
match the maximum of damping for each particular application.
alloys, imbibed in a metallic matrix, specifically designed for showing very high damping
coefficient, with the characteristic modulus of the metallic materials.
In the present work we present the damping behavior of such metal matrix composites, has been
studied by Mechanical Spectroscopy, as a function of temperature, between 150 K and 400 K,
and for different frequencies, between 3x10-3 and 3 Hz. These results are very promising,
because the internal friction spectra show a very high maximum linked to the thermo elastic
martensitic transformation, as well as a high damping background, in a very broad range in
temperature. Besides, the temperature of the maximum of damping can be controlled, in order to
match the maximum of damping for each particular application.
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The internal-friction spectra of a thermoelastic martensitic transformation are usually obtained as a function of temperature with T˙!=0 and show three-phase transition, transitory, and... more
The internal-friction spectra of a thermoelastic martensitic transformation are usually obtained as a function of temperature with T˙!=0 and show three-phase transition, transitory, and intrinsic-contributions. This paper proposes a systematic method to analyze these internal-friction spectra. Indeed, two different procedures are derived. The first one, with the support of an isothermal spectrum (T˙=0), allows one to decompose the internal-friction spectrum
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ABSTRACT We present an accurate study by AC calorimetry on the thermoelastic martensitic transformation in Cu–Al–Ni shape memory alloys, both under quasi-isothermal conditions and by using a dynamic method. The AC calorimetry results... more
ABSTRACT We present an accurate study by AC calorimetry on the thermoelastic martensitic transformation in Cu–Al–Ni shape memory alloys, both under quasi-isothermal conditions and by using a dynamic method. The AC calorimetry results suggest that the martensitic transformation exhibits some kinetic effects strongly dependent on the temperature rate, in agreement with internal friction results. Calorimetric results obtained by DSC do not exhibit this behaviour, but dynamic measurements obtained under oscillating fields show a net dependence on the temperature rate.
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ABSTRACT Export Date: 18 June 2013, Source: Scopus
Research Interests: Dislocations and Iron
ABSTRACTIn the last decades there was a growing interest in developing new light-weight intermetallic alloys, which are able to substitute the heavy superalloys at a certain temperature range. At present a new Ti-Al-Nb-Mo family, called... more
ABSTRACTIn the last decades there was a growing interest in developing new light-weight intermetallic alloys, which are able to substitute the heavy superalloys at a certain temperature range. At present a new Ti-Al-Nb-Mo family, called TNM™ alloys, is being optimized to fulfill the challenging requirements. The aim of the present work was to study the microscopic mechanisms of defect mobility at high temperature in TNM alloys in order to contribute to the understanding of their influence on the mechanical properties and hence to promote the further optimization of these alloys. Mechanical spectroscopy has been used to study the internal friction and the dynamic modulus up to 1460 K of a TNM alloy under different thermal treatments. These measurements allow to follow the microstructural evolution during in-situ thermal treatments. A relaxation process has been observed at about 1050 K and was characterized as a function of temperature and frequency in order to obtain the activation ...
ABSTRACTNew advanced multi-phase γ-TiAl based alloys (TiAl-Nb-Mo), so called TNM alloys, have been developed to promote hot workability and to allow easier processing by conventional forging. However, to control and stabilize the final... more
ABSTRACTNew advanced multi-phase γ-TiAl based alloys (TiAl-Nb-Mo), so called TNM alloys, have been developed to promote hot workability and to allow easier processing by conventional forging. However, to control and stabilize the final microstructure, specific processing and further thermal treatments are required. In the present work we used mechanical spectroscopy techniques to obtain a better understanding of the microstructural mechanisms taking place at high temperature applying two different heat treatments. Internal friction spectra and dynamic modulus evolution have been measured in an inverted torsion pendulum up to 1220 K. A stable relaxation peak was observed in both cases at about 1050 K for 1 Hz. Spectra acquired at several frequencies between 0.01 Hz and 3 Hz allow us to measure the activation parameters of this peak. In addition, a high temperature background (HTB) has been observed. This HTB, which has been found to be dependent on thermal treatments, has been analyz...
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Page 1. Materials Science Forum Vols. 366-368 (2001) pp 32-73 © (2001) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF. 366-368.32 1.2 Mechanical Spectroscopy /. San Juan 1.2.1 Introduction to ...
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The elastic properties of Cu-Al-Ni single crystals have been studied during forward and reverse martensitic transformation by dynamic mechanical analysis. Measurements were performed for two alloys, occurring in austenitic (Cu-14%Al-4%Ni)... more
The elastic properties of Cu-Al-Ni single crystals have been studied during forward and reverse martensitic transformation by dynamic mechanical analysis. Measurements were performed for two alloys, occurring in austenitic (Cu-14%Al-4%Ni) and martensitic (Cu-13.7%Al-3%Ni) phases at room temperature. Investigation of elastic and damping properties was performed for several frequencies of the oscillating force. Evolution of damping in cooling/heating measurements gave information
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ABSTRACT The anelastic relaxations observed between 100 and 600 K for a very high purity magnesium are presented. The performed experiences show an internal friction peak P1 placed around 410 K whose activation parameters are determined... more
ABSTRACT The anelastic relaxations observed between 100 and 600 K for a very high purity magnesium are presented. The performed experiences show an internal friction peak P1 placed around 410 K whose activation parameters are determined (v = 1000b3, HP1 = 1 eV). The P1 behaviour is similar to that of the P1 peak observed in 99.9999% Al around 450 K. So, the P1 relaxation in magnesium may be attributed to dislocations glide ruled by jogs climb and vacancies diffusion along the dislocation line.Lors de cet article nous présentons les relaxations anélastiques observées entre 100 et 600 K dans un magnésium de très haute pureté. Les resultats expérimentaux montrent un pic de frottement intérieur P1 situé autour de 410 K. Les paramétres d'activation de P1 ont été déterminés (v = 1000b3, HP1 = 1 eV). Le comportement de P1 est similaire à celui du pic P1 observé dans l'aluminium 99.9999% autour de 450 K. Nous pouvons donc attribuer la relaxation P1 du magnésium au glissement des dislocations contrǒlé par la montée de crans et la diffusion de lacunes le long de la dislocation.
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Internal friction measurements with a superimposed bias stress have provided evidence for geometrical kink migration on screw dislocations in iron. This intrinsic process causes a relaxation phenomenon in internal friction which has been... more
Internal friction measurements with a superimposed bias stress have provided evidence for geometrical kink migration on screw dislocations in iron. This intrinsic process causes a relaxation phenomenon in internal friction which has been identified with the occurrence of a subpeak (below 20 K) of the α-peak. The effect of different bias stress has allowed us to evaluate the kink migration
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The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases... more
The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function of alloy concentration has ...
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ABSTRACT The detailed arrangement of dislocations in cells and sub-boundaries is ruled by the dislocation energy minimization principle in a recovery process. In order to determine the exact process, the mechanical spectroscopy... more
ABSTRACT The detailed arrangement of dislocations in cells
and sub-boundaries is ruled by the dislocation
energy minimization principle in a recovery process.
In order to determine the exact process, the
mechanical spectroscopy technique has been
chosen because the dislocation structure is subjected
to stress in conditions where irreversible
changes do not appear. A relaxation peak appears
at around 0.45Tm(T m is the melting temperature)
but only if cell walls are present. It disappears in
the well-organized dislocation structure as occurs
after creep tests. This peak is used to follow the
reorganization of the dislocation during thermomechanical
treatments.
and sub-boundaries is ruled by the dislocation
energy minimization principle in a recovery process.
In order to determine the exact process, the
mechanical spectroscopy technique has been
chosen because the dislocation structure is subjected
to stress in conditions where irreversible
changes do not appear. A relaxation peak appears
at around 0.45Tm(T m is the melting temperature)
but only if cell walls are present. It disappears in
the well-organized dislocation structure as occurs
after creep tests. This peak is used to follow the
reorganization of the dislocation during thermomechanical
treatments.
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New high-damping metal matrix composites have been developed, by embedding powders of Cu–Al–Ni shape memory alloys with two different metallic matrices (In–10wt.%Sn and In–Sn eutectic alloys). The damping properties have been... more
New high-damping metal matrix composites have been developed, by embedding powders of Cu–Al–Ni shape memory alloys with two different metallic matrices (In–10wt.%Sn and In–Sn eutectic alloys). The damping properties have been characterized using a sub-resonant torsion pendulum. High damping values were obtained in a wide range of temperature. In the present work, the influence of the matrix and the shape
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The anelastic behaviour of Al–Li alloys is studied in the temperature range between room temperature and 400 K. The internal friction technique is shown to be very sensitive to the microstructural changes that take place at these... more
The anelastic behaviour of Al–Li alloys is studied in the temperature range between room temperature and 400 K. The internal
friction technique is shown to be very sensitive to the microstructural changes that take place at these temperatures. A
low-temperature shoulder (LTS) that appears from 270 to 400 K in the first heating run, is attributed to the growth of d%
precipitates during heating. The experimental behaviour of the internal friction spectra under different microstructural and
experimental conditions allows one to attribute this LTS to the stress-induced Li–Li reorientation process, similar to the Zener
effect, but in an unstable microstructural situation where small d% precipitates are present. © 1998 Elsevier Science S.A. All rights
reserved.
friction technique is shown to be very sensitive to the microstructural changes that take place at these temperatures. A
low-temperature shoulder (LTS) that appears from 270 to 400 K in the first heating run, is attributed to the growth of d%
precipitates during heating. The experimental behaviour of the internal friction spectra under different microstructural and
experimental conditions allows one to attribute this LTS to the stress-induced Li–Li reorientation process, similar to the Zener
effect, but in an unstable microstructural situation where small d% precipitates are present. © 1998 Elsevier Science S.A. All rights
reserved.
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... 149183. [12] V. Recarte, RB Pérez-Sáez, EH Bocanegra, ML No and J. San Juan, Metall. Mater. Trans. A 33A (2002), pp. 25812591. View Record in Scopus | Cited By in Scopus (39). Corresponding Author Contact Information Corresponding... more
... 149183. [12] V. Recarte, RB Pérez-Sáez, EH Bocanegra, ML No and J. San Juan, Metall. Mater. Trans. A 33A (2002), pp. 25812591. View Record in Scopus | Cited By in Scopus (39). Corresponding Author Contact Information Corresponding author. ...
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New metal matrix composites were developed with a view to elaborating high-damping materials. These composites were produced by infiltrating a relatively high amount of Cu–Al–Ni shape memory alloy particles with soft metallic matrices.... more
New metal matrix composites were developed with a view to elaborating high-damping materials. These composites were produced by infiltrating a relatively high amount of Cu–Al–Ni shape memory alloy particles with soft metallic matrices. Details on the processing method as well as on the composite microstructure are given in the present paper. An inverted torsion pendulum was used to determine the damping capacity tan δ. High damping values were measured, what implies a promising future for these composites as high-damping materials. The influence of thermal treatments on the microstructure and on the thermoelastic martensitic transformation is discussed. The damping capacity of these materials is associated with the mobility of the martensite interfaces, and a synergetic interaction between the particles and the matrices is suggested.
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ABSTRACT A single crystal Cu14%Al4%Ni shape memory alloy in austenitic phase was studied by Brillouin spectroscopy to analyse angular dispersion of Rayleigh surface waves in the planes (0 0 1) and (1 1 0). Measurements were made at room... more
ABSTRACT A single crystal Cu14%Al4%Ni shape memory alloy in austenitic phase was studied by Brillouin spectroscopy to analyse angular dispersion of Rayleigh surface waves in the planes (0 0 1) and (1 1 0). Measurements were made at room temperature using a tandem-type Fabry-Perot interferometer (JRS Scientific Instruments). Experimental results permitted determination of three independent elastic constants and anisotropic Young's modulus. In the (1 1 0) plane the pseudo-surface waves were found to occur, which---in the context of the past literature data---is unusual for cubic crystals of anisotropy coefficient higher than one. The elastic tensor components determined were used for simulation of surface phonons by the finite element method. The surface phonon velocities obtained were compared with the experimental results and the results of calculations based on the available analytical expressions for the phonon velocities for high-symmetry directions. Particular attention was paid to the relation between the elastic constants (anisotropy coefficient) and the depth of surface phonon penetration.
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ABSTRACT In this work, we carry out a detailed study, by in-situ Transmission Electron Microscopy (in-situ TEM), focused on two single-crystals of Cu-Al-Ni shape memory alloys with different transformation temperatures. The first single... more
ABSTRACT In this work, we carry out a detailed study, by in-situ Transmission Electron Microscopy (in-situ TEM), focused on two single-crystals of Cu-Al-Ni shape memory alloys with different transformation temperatures. The first single crystal is in beta phase at Room Temperature (RT) and has been cycled under stress, by super-elastic effect, inside the TEM. Two different mechanisms for the nucleation of β'3 and γ'3 martensite phases were observed: a) Martensite can nucleate on dislocations during super-elastic tests and when withdrawing the stress, the reverse transformation takes place by the disappearance of the martensite plate on the dislocation. b) During mechanical cycling martensite plates nucleate in other plates. The second single crystal is in martensite phase at RT, and when the stress is applied different mechanisms are observed: a) Reorientation and interface motion of the plates under the external applied stress, b) nucleation of mobile dislocations inside the martensite. A quantitative analysis of the experimental results, having into account the images and the diffraction patterns, has been realized and different mechanisms have been proposed to explain the experimental results.
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The effect of thermal aging at 473 K on martensitic transformation characteristics have been studied in the Cu–Al–Ni shape memory alloys. An increase of martensitic transformation temperatures as a result of aging has been observed.... more
The effect of thermal aging at 473 K on martensitic transformation characteristics have been studied in the Cu–Al–Ni shape memory alloys. An increase of martensitic transformation temperatures as a result of aging has been observed. Furthermore, the martensitic transformation shows an evolution with aging time from a single β3 ⇒ β′3 structural transformation to a β3 ⇒ γ′3 + β′3 transformation. Using internal friction and thermoelectric power measurements, as well as specific thermal treatments, it has been determined that the mechanism responsible for this evolution is an increase in the degree of order, thus rejecting the participation of a γ1 precipitation process. Finally, the increase of order at the next nearest neighbors has been established as the main factor responsible of the evolution of the martensitic transformation characteristics.
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The atomic order has a strong influence on the martensitic transformation behavior in Cu-based shape memory alloys. In this work we have studied the influence of the quenching and postquench aging treatments on the atomic order of the... more
The atomic order has a strong influence on the martensitic transformation behavior in Cu-based shape memory alloys. In this work we have studied the influence of the quenching and postquench aging treatments on the atomic order of the metastable β phase obtained by quenching in Cu–Al–Ni shape memory alloys by means of thermoelectric power (TEP) measurements. The initial evolution of TEP during aging shows two clear stages where TEP value decreases. These two TEP stages are interpreted as ordering processes at nearest neighbors (B2 order), and ordering processes at next nearest neighbors (L21 order), respectively. The analysis of the isothermal kinetics during aging at different temperatures has allowed us to determine the activation energies for both ordering processes.
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This work presents careful adiabatic calorimetry measurements of the temperature memory effects on a Cu-Al-Ni shape memory alloy single crystal. These effects, which appear after partial martensitic transformations, have been... more
This work presents careful adiabatic calorimetry measurements of the temperature memory effects on a Cu-Al-Ni shape memory alloy single crystal. These effects, which appear after partial martensitic transformations, have been systematically studied. The subsequent delay of the transformation as a function of the thermal history is described by means of a straightforward model, which makes full use of the phase
Research Interests: Engineering, Polymorphism, Kinetics, Applied Physics, Mathematical Sciences, and 15 morePhysical sciences, Shape Memory Alloy, Thermal history, Phase Transformation, Heat Capacity, Single Crystal, Memory Effect, Low Temperature, Martensitic Transformation, Copper Alloy, Shape Memory Effect, Thermal Cycling, Specific Heat, Aluminium Alloy, and Nickel Alloy
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Small grains of an intermetallic phase with an approximate composition Cu(In,Sn)2were observed in a metal matrix composite obtained from powders of a Cu–Al–Ni shape-memory alloy and an In–Sn matrix alloy. Samples of this composite were... more
Small grains of an intermetallic phase with an approximate composition Cu(In,Sn)2were observed in a metal matrix composite obtained from powders of a Cu–Al–Ni shape-memory alloy and an In–Sn matrix alloy. Samples of this composite were prepared for transmission electron microscopy and the crystal structure of the intermetallic phase was carefully investigated by applying electron diffraction techniques (microdiffraction, convergent-beam electron diffraction and precession), based on the analysis of the symmetry and the relative positions of reflections in the zero- and high-order Laue zones. It was found that the intermetallic phase has a body-centred tetragonal unit cell with lattice parametersa= 0.70 (3) nm andc= 0.56 (2) nm. Its crystal symmetry can be described by theI4/mcm(No. 140) space group.
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ABSTRACT Among the different Cu-based shape memory alloys, the Cu–Al–Be family exhibits a particular technological interest for intermediate and low temperature applications. In this work we studied the martensitic transformation behavior... more
ABSTRACT Among the different Cu-based shape memory alloys, the Cu–Al–Be family exhibits a particular technological interest for intermediate and low temperature applications. In this work we studied the martensitic transformation behavior of Cu–Al–Be single crystalline shape memory alloys with three different concentrations. The influence of four specific thermal treatments of quenching and aging on the transformation temperatures has been studied by differential scanning calorimetry and compared with similar studies by mechanical spectroscopy. The analysis of the influence of thermal treatments on the martensitic transformation behavior allows optimize a treatment useful for all the alloys transforming between 200 K and 400 K, avoiding both stabilization and precipitation. In addition, an anomalous jerky behavior has been reported for the alloy with low transformation temperatures, which is discussed in terms of the possible mechanisms.
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The study of anelastic relaxation by means of mechanical spectroscopy gives a unique insight into the mechanisms of defect mobility, and provides crucial information for the development of new intermetallic materials. In this work, a new... more
The study of anelastic relaxation by means of mechanical spectroscopy gives a unique insight into the mechanisms of defect mobility, and provides crucial information for the development of new intermetallic materials. In this work, a new high-temperature mechanical spectrometer, working up to 1800K, is used to perform such study in order to better understand the underlying processes controlling plasticity in an advanced Fe-38% Al intermetallic.The measured internal friction spectra, as a function of temperature for different frequencies, show one internal friction peak at about 1100K with a background increasing exponentially with temperature up to 1350K. In this work we apply a model that gives a consistent description of the high-temperature internal friction background in order to obtain the parameters characterizing the involved relaxation processes: Hact=5.4±0.2eV and τ0=1.4×10−19s. This apparent activation energy of the high-temperature background is compared with results in the literature obtained by creep tests and discussed in terms of the possible microscopic mechanisms. Moreover, the subtraction of the obtained background allowed a more precise measure of the activation enthalpy for the 1100K relaxation peak: Hpeak=2.98±0.02eV. We conclude that the mechanisms operating in this temperature range should be related to those controlling creep in these materials.
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ABSTRACT The metastabie $\beta$ phase in Cu-based shape memory alloys (SMA) undergoes two order-disorder transitions during quenching from high temperature. First, it undergoes a B2 ordering at the nearest neighbors and then a second one... more
ABSTRACT The metastabie $\beta$ phase in Cu-based shape memory alloys (SMA) undergoes two order-disorder transitions during quenching from high temperature. First, it undergoes a B2 ordering at the nearest neighbors and then a second one at the next nearest neighbors that has nor been clearly established. The kind of order obtained and the ordering evolution during aging at low temperature influence on the martensitic phase since it inherits the atomic order of the $\beta$ phase. Neutron Powder Diffraction measurements have been performed at room temperature in a fully ordered alloy (Cu-27.4 al-3.6 Ni at.%) obtained after quenching from 1173 K and aged during 2 hours at 473 K. The differences in the neutron scattering factors for Ni and Cu atoms promotes differences in reflestions depending on the kind of order (dO$_3$ or L2$_1$). Rietveld analysis allows to conclude that a L2$_1$ order at next nearest neighbors is present in the ordered phase.
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ABSTRACT The precipitation of the stable phases in Cu-Al-Ni shape memory alloys (SMA) limits the maximum using temperature since the decomposition of $\beta$ phase degrades very quickly the martensitic transformation. In this paper, the... more
ABSTRACT The precipitation of the stable phases in Cu-Al-Ni shape memory alloys (SMA) limits the maximum using temperature since the decomposition of $\beta$ phase degrades very quickly the martensitic transformation. In this paper, the precipitation processes of the metastable $\beta$ phase during heating in a Cu-14.37 Al-4.2 Ni (wt. %) SMA processed by powder metallurgy have been studied by Differential Scanning Calorimetry (D.S.C.) and in situ neutron powder diffraction. The pro-eutectoid $\gamma_1$; precipitation and the eutectoid decomposition has been observed during heating, followed by the posterior dissolution at higher temperature. The transformation temperatures have been determined by D.S.C. The Rietveld analysis performed on the neutron diffraction spectra allows to determine the volume fraction of the different precipitated phases and their evolution during heating. The activation energy of the primary $\gamma_1$, precipitation has been determined.
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Powder metallurgy Cu-AI-Ni shape memory alloys show excellent thermomechanical properties, being the fracture behavior close to the one observed in single crystals. However, the microstructural mechanisms responsible of such behavior are... more
Powder metallurgy Cu-AI-Ni shape memory alloys show excellent thermomechanical properties, being the fracture behavior close to the one observed in single crystals. However, the microstructural mechanisms responsible of such behavior are still under study. In this paper we present the characterization of the dislocations present in these alloys by Large Angle Convergent Beam Electron Diffraction (LACBED) in two different stages of the elaboration process: after HIP compaction and after hot rolling.
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ABSTRACT
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From a technological point of view, the most relevant mechanical properties of shape memory alloys, such as shape memory, superelastic effect, and pseudoelastic effect, are related to first-order displacive and diffusionless martensitic... more
From a technological point of view, the most relevant mechanical properties of shape memory alloys, such as shape memory, superelastic effect, and pseudoelastic effect, are related to first-order displacive and diffusionless martensitic transformation (MT) between the ...
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Internal friction measurements have been performed in order to study the Li mobility in Al-Li alloys. Coherent δ′ precipitation (nonequilibrium diffusion process) promotes a low temperature background increase according to Schoeck’s... more
Internal friction measurements have been performed in order to study the Li mobility in Al-Li alloys. Coherent δ′ precipitation (nonequilibrium diffusion process) promotes a low temperature background increase according to Schoeck’s theory. A stable Pz relaxation has been observed at around 460 K (∼1 Hz). The analysis of the behaviour of this relaxation allows us to identify the Pz peak with the Zener relaxation associated to the stress induced Li-Li pairs reorientation. The relaxation parameters lead us to determine the activation energy and the diffusion coefficient of Li. Zener relaxation has been observed in Al-Li alloys.
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In the present work, the martensite nucleation on dislocations has been observed. Cu–Al–Ni shape memory alloys have been superelastic cycled inside the transmission electron microscope. The in situ experiences show that the dislocations... more
In the present work, the martensite nucleation on dislocations has been observed. Cu–Al–Ni shape memory alloys have been superelastic cycled inside the transmission electron microscope. The in situ experiences show that the dislocations in β phase can be a nucleation site for Γ3′ and β3′ martensites, which at the same time have been characterized by electron diffraction. The martensite plates
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JI Pérez-Landazábala) and V. Recarte Departamento de Fısica, Universidad Pública de Navarra, Campus de Arrosadia s/n, 31006 Pamplona, Spain RB Pérez-Sáez Departamento de Fısica Materia Condensada, Facultad de Ciencias, Universidad del... more
JI Pérez-Landazábala) and V. Recarte Departamento de Fısica, Universidad Pública de Navarra, Campus de Arrosadia s/n, 31006 Pamplona, Spain RB Pérez-Sáez Departamento de Fısica Materia Condensada, Facultad de Ciencias, Universidad del Paıs Vasco/EHU, ...
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A single crystal with a selected composition of a Cu–Al–Ni shape memory alloy, undergoing two martensitic phase transformations when cooling from the common parent phase, β3→β3′+γ3′, has been studied by adiabatic calorimetry. As the... more
A single crystal with a selected composition of a Cu–Al–Ni shape memory alloy, undergoing two martensitic phase transformations when cooling from the common parent phase, β3→β3′+γ3′, has been studied by adiabatic calorimetry. As the coexistence of two different martensites has a strong influence on the transformation kinetics, both the forward and the reverse phase martensitic transformation have been carefully studied
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A thermodynamic study, based on high-sensitivity adiabatic calorimetry, of the martensitic transformation undergone by Cu–Al–Ni shape memory alloys is presented. From the specific heat data, the thermodynamic function values, and in... more
A thermodynamic study, based on high-sensitivity adiabatic calorimetry, of the martensitic transformation undergone by Cu–Al–Ni shape memory alloys is presented. From the specific heat data, the thermodynamic function values, and in particular the crystal free energy, as functions of temperature, have been obtained. These results have permitted a careful estimation of the phase transformation temperatures of each β3′ martensite plate