M. Arciniegas, J. M. Manero, J. Gil Mur, Technical University of Catalonia, Barcelona, Spain; J. Peņa, Elisava Escola Superior de Disseny, Barcelona, Spain
In order to improve the understanding of the thermoelastic phase transformation in TiNi shape memory alloys and its relation with their microstructures, two commercial alloys, austenitic and martensitic respectively, were studied by means of instrumented cyclic nanoindentation. Different test conditions were applied in order to evidence the transformation on the P-h curve obtained and calculate the contact pressure required for the transformation to begin. Also, based on an energy relation, a recovery percent was determined and the relation between microstructure and shape memory properties analysed under the tested conditions. The results permitted to identify hysteresis loops between unload and reload on all load-displacement curves obtained in both alloys. The loops were associated to the thermoelastic phase transformation that takes place in this type of materials. Also, a recovery index, ns, was calculated, based on the energy absorbed during the load, unload and reload portions, from the most representative results. According to the ns values, a saturation process takes place, in which the martensite induced by stress is stabilized, producing a stress-shielding effect.
Summary: In order to improve the understanding of the thermoelastic phase transformation in TiNi shape memory alloys and its relation with their microstructures, two commercial alloys, austenitic and martensitic respectively, were studied by means of instrumented cyclic nanoindentation. Different test conditions were applied in order to evidence the transformation on the P-h curve obtained and calculate the contact pressure required for the transformation to begin. Also, based on an energy relation, a recovery percent was determined and the relation between microstructure and shape memory properties analysed under the tested conditions.
The results permitted to identify hysteresis loops between unload and reload on all load-displacement curves obtained in both alloys. The loops were associated to the thermoelastic phase transformation that takes place in this type of materials. Also, a recovery index, ns, was calculated, based on the energy absorbed during the load, unload and reload portions, from the most representative results. According to the ns values, a saturation process takes place, in which the martensite induced by stress is stabilized, producing a stress-shielding effect.
