RECOVERY AND RECRYSTALLIZATION PROCESSES IN TI-PD-NI HIGH-TEMPERATURESHAPE-MEMORY ALLOYS

The Ti-Pd-Ni alloys are promising high temperature shape memory alloys . To improve the high temperature shape memory characteristics, a prop er thermomechanical treatment is useful, and the understanding of reco very and recrystallization processes is important in this context. For this purpose, the recovery and recrystallization processes in the all oys were studied in detail by micro-Vickers hardness test, differentia l scanning calorimetry and transmission electron microscopy. As a resu lt, a close relationship was found between the recovery, recrystalliza tion and the reverse transformation of the alloys, and the relationshi p was explained by a large difference in diffusion rate in the I,arent and in the martensite. This result indicates that the recovery and re crystallization in the present alloys are controlled by the reverse tr ansformation temperatures of the present alloys. Other features of the softening in hardness are discussed in detail based on electron micro scopy observations. (C) 1997 Acta Metallurgica Inc.