Martensitic transformation of NiTi studied at the nanometer scale by local mechanical spectroscopy

This paper presents the first local mechanical spectroscpy study of the martensitic transformation in NiTi alloys. The probed volume at a given temperature is in the range of 10 exp -3 mu m exp 3 with a position drift upon temperature scanning maintained < 50 nm/K. A substructure of the direct transformation peak composed of several maxima has been observed. This substructure may be explained either by twin motion inside a single martensite plate, or by the growth of several plates successively developing inside the probed volume. The comparison of the local transformation temperature with the global extent of the transformation confirms that the beginning of the direct transformation and the end of the reverse transformation occurs at the sample's surface.