Surface relief phenomenon in a NiTi shape memory alloy rod

The surface relief phenomenon is one of the interesting properties of shape memory alloys. In this paper, this phenomenon in a NiTi shape memory alloy rod is investigated quantitatively using a temperature controllable atomic force microscope. The surface reflection, which depends heavily on the surface roughness, is studies quantitatively with different incident angles and incident directions. It is found that the incident angle alpha has a slight effect on the distribution of theta, which is the angle between the real reflective direction and the ideal one. The material is almost uniform in any direction, despite that only one incident angle and four directions have been analyzed. At room temperature (martensite phase), theta mainly falls to around 3. While at 100 degreesC (austenite phase), a large portion of 0 shifts to around 20degrees. In order to obtain a ratio of change over 0.5, theta is expected to be at around 3degrees.