Phenomenological analysis of martensitic transformation in cold-rolled TiNi-base shape memory alloys

The martensitic transformation in cold-rolled TiNi-base shape memory alloys has shown that the first reverse martensitic transformation temperature (A (1)*) increases with an increasing amount of cold rolling due to the increm ent of the transformation energy barrier introduced by cold-rolling induced dislocations. Meanwhile, the increment of A(1)* temperature increases line arly with an increase in the specimen's solution-treated hardness. A phenom enological analysis from the thermodynamic viewpoint of cold-rolling induce d dislocations can elucidate these features successfully. After the first r everse transformation, the strengthening effects of retained dislocations o n martensitic transformation temperatures follow the equation M* = T-O - K Delta sigma (ys). The K value is found to be proportional to the specimen's solution-treated hardness, because the harder specimen has the stronger in teraction of martensite plates and dislocations induced by cold rolling. Th e thermal hysteresis of A(2)* - M*, associated with the frictional work dur ing the transformation, does not obviously change in the cold-rolled TiNi-b ase shape memory alloys. (C) 2001 Elsevier Science B.V. All rights reserved .