Room temperature nanoindentation creep of nanograined NiTiW shape memory alloy thin films

In this paper, the creep behaviors of NiTiW thin films at various W contents (2.6-33.6%) were investigated using the nanoindentation creep testing method. With W content ranging from 2.6 at.% to 4.5 at.%, the films are strengthened and exhibit a much reduced strain rate ϵ˙= 6.76 × 10− 4 s− 1 indicating the highest creep resistance. With further increase in W content beyond 4.5 at.% the strain rate increases and therefore the creep resistance of films decreases gradually. The stress exponents were calculated from the loading curves. The results show that stress exponent for NiTi was 8.2 and increased to 20.5 for NiTiW (2.6) and 22.9 for NiTiW (4.5) and decreased rapidly to 9.5 after increasing the W concentration from 9.1 to 33.6 at.%. The mechanism for the room temperature creep is discussed in the framework of dislocation dynamics. Grain boundaries play an important role in creep behavior. Studying the deformation behavior of NiTiW thin films has technological importance because of their various applications in micro- and nano-electro-mechanical systems.