Grain refinement of NiTi shape memory alloy thin films by W addition
2013
Kaur, Navjot | Dewindara Kaura,
The present research explores the novel approach to achieve grain refinement in NiTi shape memory alloy thin films by adding W in the matrix of NiTi. It involves production of NiTiW shape memory alloy thin films by Co-sputtering of NiTi and W targets. The grain size of B2-NiTi decreases with increasing W content, due to the immiscible W layer obstructing its grain growth. Moreover addition of W induces the B2–R single step transformation by suppressing thermally induced martensite phase due to grain size refinement below 40nm. With W content ranging from 2.6at% to 4.5at%, the films are strengthened and can reach highest hardness and elastic modulus of 32.8±2.7GPa and 167.83±8.64GPa, respectively. With further increase in W content, the mechanical properties of films decrease gradually. This behavior can be explained in terms Hall–Petch theory and lattice distortion of NiTi crystals with increasing the W content.
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