Stress-induced martensitic transformation in Fe-Ni bicrystals

The effect of applied stress on martensitic transformation behaviour near the grain boundary was examined using Fe-32 at.% Ni bicrystals containing a 90 degrees (211) tilt or a 90 degrees (211) twist grain boundary focusing on the martensite-start stress (sigma (M)), the morphology of martensites and the variant selection. The sigma (M) for single crystals and tilt boundary bicrystals increases almost linearly with increasing temperature (T), and the sigma (M)-T relation for tilt boundary bicrystals is situated in the higher temperature side than that for single crystals. In contrast, the a of the twist boundary bicrystals exists between the correlated sigma (M)-T relations for single crystals and tilt boundary bicrystals. The variant selection near the tilt boundary is not sensitive to applied stress; some variants with the habit plane almost parallel to the boundary were symmetrically formed similar to those in the thermal transformation. The effect of loading axis to grain boundary on the martensitic transformation behaviour was also investigated. (C) 2001 Acta Materialia Inc. Published ky Elsevier Science Ltd. All rights reserved.