Dynamics of propagating phase boundaries in NiTi

Propagating boundaries of phase transformation have been generated in polycrystalline NiTi specimens under a tensile impact loading condition. Multiple strain gages were used to monitor the time evolution of the strain at different spatial locations in the specimen. Nucleation and propagation of multiple phase fronts were detected in these experiments; the phase front speed was found to be in the range between 37 and 370 m/s. The strain measurements were interpreted through the one-dimensional analysis of Abeyaratne and Knowles [1997. On the kinetics of an austenite→martensite phase transformation induced by impact in Cu–Al–Ni shape-memory alloy. Acta Mater. 45, 1671–1683] and a model of partial phase transformation in the polycrystalline specimen. The driving force for the motion of the phase front was evaluated from the measurements in order to establish the kinetic relation.