On the Origin of the Two Way Shape Memory Effect in Cu-Zn-Al Alloys

Several training procedures have been found suitable to induce the two way shape memory effect (TWSME) in copper based alloys. Complex dislocation arrangements can be produced by transformation cycling, which are believed to be the cause of the TWSME. Small martensite plates can be stabilized, serving as origin of subsequent transformations, or deformation around second phase precipitates are used. In this work, the role of the dislocations arrangements is investigated. It is shown that the stress field around the dislocations leads to the formation, in the β phase, above the Ms, of small martensite plates. These martensites do not necessarily correspond to the trained variant. Complex defects consisting of dislocations and heavily deformed martensites are thus produced. The role of these complex defects on the TWSME is discussed and possible mechanisms are suggested

Eleventh European Powder Diffraction Conference, Warsaw, September 19-22, 2008, available at:https://www.degruyter.com/view/title/320388.

We have investigated an Fe-30Mn-4Si shape memory alloy to clarify the effect, on the bulk texture, of the shear layers resulting from two different thermo-mechanical treatments. XR analysis has shown the existence of texture heterogeneity through the rolled sheet's thickness, due to the effect of friction between sheet and rolls. Neutron diffraction revealed that textured layers on the sheet's surface affect the whole volume. The texture found on the surface of the sheet rolled at 600 degrees C is the most favourable for the γ ->epsilon martensitic transformation which is the origin of the shape memory effect. Comparing these results with those obtained on sheets rolled at room temperature, we found that shear deformation gradients produce changes in the bulk material texture. Tensile tests initially induce the martensitic transformation in those grains favourably oriented. As a result, these favourable orientations disappear in the remnant austenite. © 2009, Oldenbourg Verla

Effects of B2 nanoprecipitates on the phase stability and pseudoelastic behavior of Fe-Mn-Al-Ni shape memory alloys

Samples of a Fe-Mn36-Al15-Ni7.5 shape memory alloy were subjected to different thermal treatments at 200ºC (namely for 0 min, 10 min, 20 min and 3 h) in order to evaluate the evolution of the coherent precipitates related to the pseudoelastic behavior. After performing the thermal treatments, samples were studied by means of electrical resistivity in experiments aimed at evaluating the effect of precipitation on the martensitic transformation temperatures and at determining the possible effects of thermal cycling. Mechanical tests were performed to measure the degree of pseudoelastic recovery for each thermally treated sample. Evidences of pseudoelastic behavior were found even in samples subjected to a rather short treatment such as 20 min after three thermal cycles. Transmission electron microscopy (TEM) observations were performed in order to identify the distribution and size of B2 nano-precipitates after the various thermal treatments

Effects of B2 nanoprecipitates on the phase stability and pseudoelastic behavior of Fe-Mn-Al-Ni shape memory alloys

Samples of a Fe-Mn36-Al15-Ni7.5 shape memory alloy were subjected to different thermal treatments at 200ºC (namely for 0 min, 10 min, 20 min and 3 h) in order to evaluate the evolution of the coherent precipitates related to the pseudoelastic behavior. After performing the thermal treatments, samples were studied by means of electrical resistivity in experiments aimed at evaluating the effect of precipitation on the martensitic transformation temperatures and at determining the possible effects of thermal cycling. Mechanical tests were performed to measure the degree of pseudoelastic recovery for each thermally treated sample. Evidences of pseudoelastic behavior were found even in samples subjected to a rather short treatment such as 20 min after three thermal cycles. Transmission electron microscopy (TEM) observations were performed in order to identify the distribution and size of B2 nano-precipitates after the various thermal treatments

Kinetics of the alpha-gamma' stress-induced martensitic transformation in a Fe–Mn–Al–Ni shape memory bicrystal

The Fe–Mn–Al–Ni pseudoelastic system has garnered interest for diverse engineering applications owing to its promising characteristics. The poor pseudoelasticity in polycrystals is generally attributed to activation of new martensite variants and the high density of dislocations close to austenite/martensite interface. High-energy synchrotron X-ray diffraction and microscopy studies on a Fe–Mn–Al–Ni bicrystal reveal the sequence of transformation, deformation mechanisms, and grain boundary effects on martensite nucleation, shedding light on its limited pseudoelasticity in polycrystalline configurations. The results highlight challenges in achieving pseudoelasticity in polycrystalline configurations due to disparities in deformation between grains and at grain boundaries.Peer ReviewedPostprint (author's final draft

Effects of B2 nanoprecipitates on the phase stability and pseudoelastic behavior of Fe-Mn-Al-Ni shape memory alloys

Samples of a Fe-Mn36-Al15-Ni7.5 shape memory alloy were subjected to different thermal treatments at 200°C (namely for 0 min, 10 min, 20 min and 3 h) in order to evaluate the evolution of the coherent precipitates related to the pseudoelastic behavior. After performing the thermal treatments, samples were studied by means of electrical resistivity in experiments aimed at evaluating the effect of precipitation on the martensitic transformation temperatures and at determining the possible effects of thermal cycling. Mechanical tests were performed to measure the degree of pseudoelastic recovery for each thermally treated sample. Evidences of pseudoelastic behavior were found even in samples subjected to a rather short treatment such as 20 min after three thermal cycles. Transmission electron microscopy (TEM) observations were performed in order to identify the distribution and size of B2 nanoprecipitates after the various thermal treatments.Fil: la Roca, Paulo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Medina, J.. Universidad Nacional del Nordeste; ArgentinaFil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Avalos, Martina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Malarria, Jorge Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Baruj, Alberto Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Sade Lichtmann, Marcos Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin