D. Treppmann et E. Hornbogen, ON THE INFLUENCE OF THERMOMECHANICAL TREATMENTS ON SHAPE-MEMORY ALLOYS, Journal de physique. IV, 7(C5), 1997, pp. 211-220
Thermomechanical treatments (TMT) are used to modify the microstructur
e of austenite or martensite by introducing lattice defects and/or par
ticles of a second phase. The temperature range extends between T grea
ter than or equal to M-d (pure ausforming) and T less than or equal to
M-f(pure marforming). In the intermediate range (M-f < T < M-d) a mor
e complex behaviour is found. TMT are discussed in a systematic manner
using NiTi-based and Cu-based alloys as examples. Transformation beha
viour and mechanical properties of TM-treated alloys are compared with
undeformed ones. The following effects can be observed for thermal tr
ansformation cycles: (al) lowering or raising of transformation temper
atures, (a2) widening or decreasing of hysteresis, (a3) induction of m
ultiple step transformation mechanisms, (a4) reduction of martensitic
retransformability (e.g. plastic deformation of martensite = marformin
g). The mechanical properties are also highly affected: (bl) increase
in pseudo yield stress, (b2) increase or decrease in shape memory stra
in, (b3) increase in conventional strength, (b4) increase in elongatio
n at fracture (by hot rolling of austenite = ausforming). It is shown
how tailor-made microstructures are obtained, which in turn provide th
e best bulk properties for specified applications of SMA in engineerin
g.