TEM observation of stress-induced martensite after nanoindentation of pseudoelastic Ti50Ni48Fe2

In the present study we show that stress-induced martensite forms during nanoindentation of a pseudoelastic shape memory alloy of type Ti50Ni48Fe2. For this purpose, we performed nanoindentation experiments using a specimen which was prepared for subsequent investigation in a transmission electron microscope (TEM). A Berkovich nanoindentation experiment into the thin part of the TEM specimen and subsequent post-mortem TEM analysis (bright field and selected area diffraction) showed that B19′ forms close to the center of the indent (distance d from the center of the indent <2 μm). Further out (2 μm < d < 5 μm), an increased dislocation density was observed. This represents direct microstructural evidence for the formation of stress-induced martensite and a simultaneous increase in dislocation density during Berkovich nanoindentation of pseudoelastic shape memory alloys.