Two-way indent depth recovery in a NiTi shape memory alloy

Controlled reversible changes in surface texture and topography are of interest to many applications, including information storage, optical communication devices, micro-fluidic instruments for drug delivery, and smart tribological surfaces for friction and wear control. Here, we demonstrate a method of inducing two-way reversible changes in an indentation made on the surface of a shape memory NiTi alloy. The two-way indent shape change is accomplished by thermomechanical training of spherical indents in NiTi shape memory alloy. After training, spherical indents exhibit two-way depth recovery: Shallow indent depth at high temperature and deep indent depth at low temperature. The reversible depth change is about 45% of the total indent depth and is stable over many cycles. The reversible depth change can have a wide range of engineering applications.