Characterization of phase transformation in shape memory alloys by atomic force microscope

An atomic force microscope operated at various temperatures is introduced to evaluate phase transformation temperature and to observe microstructure for a shape memory alloy at same time in this paper. A commercial hot-rolled TiNi shape memory alloy bar is ground, polished and etched. The specimen is then observed by atomic force microscopy at the temperature range of 20–100 ∘C in nitrogen gas. The topographies of a TiNi specimen show twinning martensite with rough surface and smooth austenite at various temperatures. The shape memory effect of the TiNi alloy is analyzed based on the shifts of the topographies obtained at various temperatures, which are used to evaluate the phase transformation temperature between martensite and austenite. The phase transformation temperature is also confirmed in a differential scanning calorimeter (DSC) experiment.