Research Interests:
Abstract. Cu-AI-Ni single crystals which present J3-P ' (quenched samples) or P-y ' (aged at 570K samples) thermally induced martensitic transformations, were submitted to compressive stresses at different temperatures. The test... more
Abstract. Cu-AI-Ni single crystals which present J3-P ' (quenched samples) or P-y ' (aged at 570K samples) thermally induced martensitic transformations, were submitted to compressive stresses at different temperatures. The test temperatures were chosen in order to have martensite-martensite stress induced transformations. The characteristics of the martensitic transformation and structural changes before and after the compression tests have been studied by means of calorimetry (DSC) and TEM. The obtained results show that when applying compressive stresses in both ensembles of samples, a non-twinned Y martensite appears. In the quenched samples it is formed through the 0'phase already present at room temperature. In the aged samples the non twinned y'phase is stress induced from the y'thermally formed (internally twinned). The amount of non twinned y'phase increases with the applied deformation, for low strain values it coexists with the ß'or y &a...
Research Interests:
ESTE TRABAJO SE ENMARCA EN LA LINEA DE ESTUDIO DE LAS TRANSFORMACIONES MARTENSITICAS ASOCIADAS A LOS MATERIALES CON MEMORIA DE FORMA. HEMOS REALIZADO UN ANALISIS DE LAS POSIBILIADES DEL SISTEMA EXPERIMENTAL DE ADQUISICION CALORIMETRICA... more
ESTE TRABAJO SE ENMARCA EN LA LINEA DE ESTUDIO DE LAS TRANSFORMACIONES MARTENSITICAS ASOCIADAS A LOS MATERIALES CON MEMORIA DE FORMA. HEMOS REALIZADO UN ANALISIS DE LAS POSIBILIADES DEL SISTEMA EXPERIMENTAL DE ADQUISICION CALORIMETRICA PUESTO EN MARCHA ASI COMO LA DETERMINACION DE LAS CONDICIONES OPTIMAS DE TRABAJO. Y HEMOS UTILIZADO DICHO SISTEMA PARA ESTUDIAR EL EFECTO DE LOS TRATAMIENTOS TERMOMECANICOS Y DEL CICLADO TERMICO SOBRE LA TRANSFORMACION MARTENSITICA DE LA ALEACION TERNARIA CU-16.13% Z-15.93% AL (%AT). EL ELEMENTO BASICO DEL SISTEMA ES UN CALORIMETRO DIFERENCIAL CON DETECTORES SEMICONDUCTORES (DMINIO DE TRABAJO: 100-400; SENSIBILIDAD: 50-400MV/W) DE TEMPERATURA VARIABLE QUE POR SU DISENO PERMITE LA MEDIDA SIMULTANEA DE OTRAS MAGNITUDES (EMISION ACUSTICA...). LA RESOLUCION EN TEMPERATURAS DISPONIBLE ES DE 0.0K K Y LA RESOLUCION EN MASA DE 4 UG. (CON T=3K/MIN). LA RELACION SENAL/RUIDO OBTENIDA PARA LAS TRANSFORMACIONES ESTUDIADAS VARIA ENTRE 5000 Y 10000. EL SISTEMA PROPO...
Research Interests:
Research Interests:
Page 1. Materials Science Forum Vols. 56-58 (1990) pp 523-528 Q © (1990) Trans Tech Publications, Switzerland n doi: 10.4028/www. scientific. net/MSF. 56-58.523 = a » Д1 I? sh I'D ¡Q. 1С SU n 7Г Materials Science Forum Vols. 56 -... more
Page 1. Materials Science Forum Vols. 56-58 (1990) pp 523-528 Q © (1990) Trans Tech Publications, Switzerland n doi: 10.4028/www. scientific. net/MSF. 56-58.523 = a » Д1 I? sh I'D ¡Q. 1С SU n 7Г Materials Science Forum Vols. 56 - S8 (1990) pp. ...
Research Interests:
ABSTRACT The study of martensitic transformations in shape memory alloys by means of techniques such as unconventional scanning calorimetry, acoustic emission and optical microscopy has made it possible to establish the existing links... more
ABSTRACT The study of martensitic transformations in shape memory alloys by means of techniques such as unconventional scanning calorimetry, acoustic emission and optical microscopy has made it possible to establish the existing links between the hysteresis cycle and the internal state of a given material We have studied the changes in the hysteresis cycle, concerning its shape, width and relevant temperatures, which are produced as a consequence of different thermal treatments and repetitive thermal cycling, for a Cu-Zn-Al single crystal. The effect of thermomechanical treatments in Cu-Zn-Al samples with different surface orientation is also studied. Relevant changes in a mixed hysteresis cycle (Cu-Al-Ni polycrystal with two martensite phases) are observed in annealing treatments. On the other hand, observation of the interfaces movement in reduced thermal cycling establishes the temperature scale and the geometrical conditions to obtain a repetitive/recoverable hysteresis cycle
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Single crystals of 82.5 wt.%Cu13.5 wt.%Al4 wt.%Ni which present the β′(18R) thermally induced martensitic transformation after quenching from 1120 K, were submitted to mechanical tests in the compression mode at different temperatures.... more
Single crystals of 82.5 wt.%Cu13.5 wt.%Al4 wt.%Ni which present the β′(18R) thermally induced martensitic transformation after quenching from 1120 K, were submitted to mechanical tests in the compression mode at different temperatures. The studied temperatures were ...
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT Ageing treatments at 620 K performed in ferromagnetic Co49Ni21Ga30 shape memory single crystals have been found to generate dense dispersions of nanometric γ′ precipitates in the austenitic matrix. These particles have a strong... more
ABSTRACT Ageing treatments at 620 K performed in ferromagnetic Co49Ni21Ga30 shape memory single crystals have been found to generate dense dispersions of nanometric γ′ precipitates in the austenitic matrix. These particles have a strong influence on the B2–L10 martensitic transformation, decreasing the overall transformation temperatures and enhancing the transformation range (difference between the temperatures for start and finish of transformation) and hysteresis. The martensitic microstructure is strongly affected as well, in such a way that the thickness of martensitic twins depends on the size and shape of particles (spherical or elongated). The results indicate that, in case of precipitation of spherical particles with diameters ∼3–5 nm, the martensitic twins can absorb the particles and the twin thickness is still considerably larger than the precipitate diameter, while growth of larger and elongated particles with a length of 10–25 nm leads to the formation of tiny twins in between the particles with thickness of ∼3–4 nm. These small martensite twins present an additional internal modulation and satellite spots in the diffraction pattern.
Research Interests:
The pseudoelastic behavior of a Co 49 Ni 21 Ga 30 ferromagnetic shape memory alloy under compression along [100] has been studied in the temperature range 300–500 K. In such a crystals, the effect of aging under a constant stress close to... more
The pseudoelastic behavior of a Co 49 Ni 21 Ga 30 ferromagnetic shape memory alloy under compression along [100] has been studied in the temperature range 300–500 K. In such a crystals, the effect of aging under a constant stress close to the critical stress to induce the martensitic transformation, produces its separation in two stages. This is due to the different ordering behavior of parent and martensite phases under aging. Increasing order of parent phase leads to a decrease of transformation temperatures, which in return leads to an increase in critical stress to induce the transformation. Aging of martensite produces its stabilization — increase in transformation temperatures. It is remarkable that this stabilization has a very slow recovery, as compared to other alloys systems, such as Cu-based shape memory alloys.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT A systematic study of the thermal energy released in the martensitic transformation undergone by a monocrystalline alloy of composition 74.41 Cu-18.18 Zn-7.41 Al (wt%) has been made. The values for ΔH in the β → M and M → β... more
ABSTRACT A systematic study of the thermal energy released in the martensitic transformation undergone by a monocrystalline alloy of composition 74.41 Cu-18.18 Zn-7.41 Al (wt%) has been made. The values for ΔH in the β → M and M → β transformations have been determined, as a function of the heat treatment and the number of cycles. The experimental results establish that the transformation enthalpy is reproducible when the initial conditions are well determined. For different samples, in thermal cycles 1 to 10, ΔH is approximately constant, and by rapid cycling, the enthalpy of the 100th cycle is slightly smaller. Thermal cycling makes the effects of heat treatment less important and smooths the picture of the transformation dynamic. A qualitative study of several features of the acoustic emission produced during the transformation, as its signal/noise ratio and waveform, has also been carried out.
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT