Multi-strengthening effects on the martensitic transformation temperatures of TiNi shape memory alloys

The multi-strengthening effects, introduced by combining cold rolling, aging and thermal cycling, on the martensitic transformation temperatures of Ti(5)0Ni(50) and Ti49Ni51 shape memory alloys have been studied by using DSC and microhardness measurements. Experimental results show that both pre-cold-rolling of Ti(5)0Ni(5)0 alloy and aging treatments of Ti49N51 alloy can impede the further introduction of dislocations during the thermal cycling and hence effectively reduce the effect of thermal cycling on transformation temperatures. For Ti(4)9Ni(51) alloy, whether the cold rolling is conducted before or after the aging treatment, the strengthening of cold rolling can significantly increase the specimen hardness but only slightly affect the following thermal cycling effect. The multi-strengthening effects on the martensitic transformation temperatures are also found to follow the equation of Ms = T-0-K Delta sigma(y). (C) 1999 Kluwer Academic Publishers.