Comparison of in situ SEM and TEM observations of thermoelastic martensitic transformation in TiNi shape memory alloy

Abstract

To quantitatively understand the thin foil effect in in situ observations of the B2 to B19A transformation in TiNi alloy, the microstructure of the B19A martensite in thin foil and bulk specimens was compared. The transformation temperatures decreased with decreasing specimen thickness. There were large habit plane variants more than several tens of micrometers in size in the area of the specimen less than 10μm thick. The critical thicknesses for reproducing the transformation behavior in the bulk material was about 20μm based on the self-accommodation morphology and 4 μm based on the twin width ratio of the (011) type II twin.