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

The multi-strengthening effects, introduced by combining cold rolling, agin g 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-col d-rolling of Ti(5)0Ni(5)0 alloy and aging treatments of Ti49N51 alloy can i mpede the further introduction of dislocations during the thermal cycling a nd hence effectively reduce the effect of thermal cycling on transformation temperatures. For Ti(4)9Ni(51) alloy, whether the cold rolling is conducte d before or after the aging treatment, the strengthening of cold rolling ca n significantly increase the specimen hardness but only slightly affect the following thermal cycling effect. The multi-strengthening effects on the m artensitic transformation temperatures are also found to follow the equatio n of Ms = T-0-K Delta sigma(y). (C) 1999 Kluwer Academic Publishers.