- Dpt. Fisica de la Materia Condensada
Facultad de Ciencia y Tecnologia
Universidad del Pais Vasco (UPV/EHU)
Aptdo 644, 48080 Bilbao
SPAIN
- Shape Memory Alloys, Intermetallics, Internal Friction, Mechanical Spectroscopy, Nanomaterials Characterization, In situ nanoindentation tests, and 5 moreMechanical Properties of Materials, Mechanical Behavior Of Materials, Smart Materials, Transmission Electron Microscopy, and Scanning Electron Microscopyedit
- I am full Professor on Physical Metallurgy at the University of the basque Country, UPV/EHU. (Since 1995)I was Visiti... moreI am full Professor on Physical Metallurgy at the University of the basque Country, UPV/EHU. (Since 1995)I was Visiting Porfessor at the Dpt. of Materials Science and Engineering of the Massachusetts Institute of technology, MIT, Cambridge USA. (2006-2007)I own a PhD on Materials Science by the Institut National of Sciences Appliquées (INSA) of Lyon, France, as well as a PhD on Physics by the University of the Basque Country (UPV/EHU), Bilbao, Spain.I am the leader of the Physical Metallurgy Research Group (GIMF) at the University of the Basque Country, Bilbao, Spain, recognized as Consolidated Research Group, by the Basque Government. The GIMF is a multidisciplinary research group involving four full Professors from the Department of Physics of Condensed Matter and the Department of Applied Physics.The GIMF is also proud of the development of the laboratories on Internal Friction and Mechanical Spectroscopy technique, pioneer in Spain, as well as the seed laboratory for the creation of the Electron Microscopy Service for Materials Science of the UPV/EHU.edit
Stress-induced martensite nucleation and further growing, in Cu–Al–Ni shape memory alloys, have been studied during in situ super-elastic tests in the transmission electron microscope. Two kinds of martensite, b 0 3 and c 0 3 , are... more
Stress-induced martensite nucleation and further growing, in Cu–Al–Ni shape memory alloys, have been studied during in situ super-elastic tests in the transmission electron microscope. Two kinds of martensite, b 0 3 and c 0 3 , 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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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... 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 213 C 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.
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Superelastic nanocompression tests are performed on different micropillars milled by focused ion beam from [0 0 1]-oriented single crystals of Cu–Al–Ni shape memory alloys. Over hundreds of cycles such micropillars exhibit reproducible... more
Superelastic nanocompression tests are performed on different micropillars milled by focused ion beam from [0 0 1]-oriented single crystals of Cu–Al–Ni shape memory alloys. Over hundreds of cycles such micropillars exhibit reproducible superelastic behavior with complete recovery at stresses around 300 MPa and stress-induced transformation strains above 5%. Upon cycling, the critical stress to induce the transformation decreases, and the transformation strain increases, both signatures of a training effect which is analyzed here in terms of the microscopic mechanisms controlling the nucleation, growth and recovery of the martensite plates. The mechanical hysteresis is characterized through the energy dissipated during closed superelastic cycles, and its evolution during cycling is discussed. The superelastic cycling of the micropillars is also found to depend on the strain rate. The highest strain rate studied here, 10 À1 s À1 , is found to impinge upon the nucleation and growth kinetics of c 0 3 and b 0 3 martensites, with the result that the mechanical hysteresis and transformation strain are reduced. Finally, specific cycling tests have been conducted at increasing maximum loads to analyze the limit for plastic deformation of the micropillar, which happens between 500 and 700 MPa.
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Shape memory alloys Cu–Al–Ni Multilayer e-Beam evaporation 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... more
Shape memory alloys Cu–Al–Ni Multilayer e-Beam evaporation 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/SiO 2 and Si/Si 3 N 4 , 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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In this work we overview the extrinsic size-effects on the martensitic transformation reported in the literature by nano compression tests in micro and sub-micrometer pillars, as well as by in situ superelastic tests at the transmission... more
In this work we overview the extrinsic size-effects on the martensitic transformation reported in the literature by nano compression tests in micro and sub-micrometer pillars, as well as by in situ superelastic tests at the transmission electron microscope. Three different size-effects are described: The increase of the critical stress for superelasticity at nano scale, the decrease of the stress for recovery during the reverse stress-induced martensitic transformation at micro and nano scale and finally the change of the selection rule for the martensitic variants promoted at micro and nano scale. New results are presented to illustrate the behavior of these size-effects and the microscopic origin of such effects is discussed. A consistent interpretation is given and explained for each one of the reported size-effects on the martensitic transformation.
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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.... more
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.
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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Severe plastic deformation (SPD) frequently induces phase transformations like decomposition of su-persaturated solid solution, dissolution of precipitates, amorphization, nanocrystallization etc. Such diffusive phase transitions are... more
Severe plastic deformation (SPD) frequently induces phase transformations like decomposition of su-persaturated solid solution, dissolution of precipitates, amorphization, nanocrystallization etc. Such diffusive phase transitions are combined with SPD-driven accelerated mass transfer. Displacive (or martensitic) phase transitions can also take place and in combination with diffusive ones have not been investigated in depth in severely deformed materials. The goal of this work is to investigate the combination of displacive (austenite4martensite) and diffusive (decomposition of supersaturated solid solution) phase transitions in two different CueAleNi shape memory alloys under the influence of high-pressure torsion (HPT). After homogenization in the one-phase (austenitic) b-area of CueAleNi phase diagram and quenching, the first alloy was in martensitic state (mainly b 0 3 martensite with a small amount of g 0 3 martensite), and the second one remained austenitic (b 3 phase). The HPT of these alloys led to the precipitation of a 1-phase in the first case and g 1-phase in the second one (as if they were annealed at an effective temperature T eff ¼ 620 ± 20 C). As a result of precipitation, the matrix in the first alloy was enriched and in the second one depleted in Al. After HPT, both alloys contained mainly b 0 3 martensite with a certain amount of g 0 3 martensite. Thus, the HPT-driven diffusive transformations (precipitation of a 1-and g 1-phase) influence the followed displacive (martensitic) transformation. Simultaneously, a dramatic grain refinement is obtained and the reported results open new possibilities to investigate the superelastic and shape memory effects in nanostructured CueAleNi alloys.
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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] L2 1 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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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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Advanced g-TiAl based intermetallics Mo-bearing have been developed to obtain the fine-grained microstructure required for superplastic deformation to be used during further processing. In the present work we have studied an alloy of... more
Advanced g-TiAl based intermetallics Mo-bearing have been developed to obtain the fine-grained microstructure required for superplastic deformation to be used during further processing. In the present work we have studied an alloy of Tie46.8Ale1Moe0.2Si (at%) with two different microstructures, as-cast material with a coarse grain size above 300 mm, and the hot extruded material exhibiting a grain size smaller than 20 mm. We have used a mechanical spectrometer especially developed for high temperature internal friction measurements to study the defect mobility processes taking place at high temperature. The internal friction spectra at different frequencies has been studied and analyzed up to 1360 K in order to characterize the relaxation processes appearing in this temperature range. A relaxation peak, with a maximum in between 900 K and 1080 K, depending on the oscillating frequency, has been attributed to Ti-atoms diffusion by the stress-induced reorientation of AleV Ti eAl elastic dipoles. The high temperature background in both microstructural states, as-cast and extruded, has been analyzed, measuring the apparent activation parameters, in particular the apparent energies of E cast (IF) ¼ 4.4 ± 0.05 eV and E ext (IF) ¼ 4.75 ± 0.05 eV respectively. These results have been compared to those obtained on the same materials by creep deformation. We may conclude that the activation parameters obtained by internal friction analysis, are consistent with the ones measured by creep. Furthermore, the analysis of the high temperature background allows establish the difference on creep resistance for both microstructural states.
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Advanced intermetallic g-TiAl based alloys, which solidify via the disordered b phase, such as the TNM þ alloy, are considered as most promising candidates for structural applications at high temperatures in aero and automotive... more
Advanced intermetallic g-TiAl based alloys, which solidify via the disordered b phase, such as the TNM þ alloy, are considered as most promising candidates for structural applications at high temperatures in aero and automotive industries, where they are applied increasingly. Particularly creep resistant mi-crostructures required for high-temperature application, i.e. fine fully lamellar microstructures, can be attained via two-step heat-treatments. Thereby, an increasing creep resistance is observed with decreasing lamellar interface spacing. Once lamellar structures reach nano-scaled dimensions, deformation mechanisms are altered dramatically. Hence, this study deals with a detailed characterization of the elevated temperature deformation phenomena prevailing in nano-lamellar TiAl alloys by the use of tensile creep experiments and mechanical spectroscopy. Upon creep exposure, microstructural changes occur in the lamellar structure, which are analyzed by the comparative utilization of X-ray diffraction, scanning and transmission electron microscopy as well as atom probe tomography. Creep activation parameters determined by mechanical characterization suggest the dominance of dislocation climb by a jog-pair formation process. The dislocations involved in deformation are, in nano-lamellar TiAl alloys, situated at the lamellar interfaces. During creep exposure the precipitation of b o phase and z-silicide particles is observed emanating from the a 2 phase, which is due to the accumulation of Mo and Si at lamellar interfaces.
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A B S T R A C T The design of the next generation of β-stabilized γ-TiAl based alloys as structural materials for high-temperature applications in aircraft engines requires the precise knowledge of the mobility of defects in the ordered β... more
A B S T R A C T The design of the next generation of β-stabilized γ-TiAl based alloys as structural materials for high-temperature applications in aircraft engines requires the precise knowledge of the mobility of defects in the ordered β o phase. To reach this goal a Mo-rich prototype alloy has been specifically produced and investigated. The mobility of defects, between 600 K and 1635 K, has been studied by mechanical spectroscopy. The internal friction spectra show a relaxation peak P1 (at 1130 K for 1 Hz) superimposed to a high-temperature background. We demonstrate that the relaxation peak is taking place inside the β o phase and measure an activation energy of E P1 = 3.55 ± 0.05 eV. An atomistic model is additionally proposed to explain this relaxation peak, which is attributed to a Zener-like mechanism of stress-induced Mo-Mo dipoles reorientation by exchange with a vacancy, and consequently the measured activation energy corresponds to the one for Mo diffusion in the β o phase.
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A continuum glassy polymer model applicable to dynamic loading J. Appl. Phys. 112, 083511 (2012) Effects of mechanical contact stress on magnetic properties of ferromagnetic film J. Appl. Phys. 112, 084901 (2012) Pyramidal dislocation... more
A continuum glassy polymer model applicable to dynamic loading J. Appl. Phys. 112, 083511 (2012) Effects of mechanical contact stress on magnetic properties of ferromagnetic film J. Appl. Phys. 112, 084901 (2012) Pyramidal dislocation induced strain relaxation in hexagonal structured InGaN/AlGaN/GaN multilayer J. Appl. Phys. 112, 083502 (2012) Resonant frequency analysis of Timoshenko nanowires with surface stress for different boundary conditions J. Appl. Phys. 112, 074322 (2012) Additional information on Appl. Phys. Lett. Journal Homepage: http://apl.aip.org/ Journal Information: http://apl.aip.org/about/about_the_journal Top downloads: http://apl.aip.org/features/most_downloaded Information for Authors: http://apl.aip.org/authors
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This work focuses on the high-temperature mechanic properties of a 3 mol% yttria zirconia polycrystals (3YTZP), fabricated by hot-pressureless sintering. Systematic measurements of mechanical loss as a function of temperature and... more
This work focuses on the high-temperature mechanic properties of a 3 mol% yttria zirconia polycrystals (3YTZP), fabricated by hot-pressureless sintering. Systematic measurements of mechanical loss as a function of temperature and frequency were performed. An analytical method, based on the generalized Maxwell rheological model, has been used to analyze the high temperature internal friction background (HTB). This method has been previously applied to intermetallic compounds but never to ceramics, except in a preliminary study performed on fine grain and nano-crystalline zirconia. The HTB increases exponentially and its analysis provides an apparent activation enthalpy which correlates well with that obtained from creep experiments. This fact shows on the one hand the plausibility of applying the generalized Maxwell model to ceramics, and on the other hand indicates the possibility of using mechanical spectroscopy as a complementary helpful technique to investigate the high temperature deformation mechanism of materials.
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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.
Research Interests:
Research Interests:
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.
Research Interests:
Research Interests:
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.
Research Interests:
Research Interests:
ABSTRACT