Effect of Ti addition on the structural, mechanical and damping properties of magnetron sputtered Ni-Mn-Sn ferromagnetic shape memory alloy thin films

Titanium (Ti) co-sputtered Ni50.4Mn34.7Sn14.9 films deposited by magnetron sputtering onto Si(1 0 0) substrates at 823K were investigated. X-ray diffraction profiles revealed the formation of highly (2 2 0)-oriented Ni-Mn-Sn-Ti austenite phase with significant decrease in grain size with increasing Ti power. Hardness (H), elastic modulus (E-r), damping (tan delta), figure of merit (FOM) and coefficient of restitution (e) of the films were evaluated using nanoindentation tests. A significant improvement in the hardness (10.5 GPa) and toughness H-3/E-r(2) (0.040) was observed in the Ni51.0Mn28.2Sn11.0Ti9.7 nanocomposite film as compared with pure Ni(50.4)Mn(34.7)Sn(14.9)films. An impact model, which incorporates material behaviour, is presented that predicts the experimentally observed material quantities, including energy dissipation metrics such as the coefficient of restitution e with high accuracy. The highest damping factor (tan delta = 0.061), high FOM (0.79) with low coefficient of restitution (e = 0.28) quantifies excellent energy dissipation capacity in the Ni51.0Mn28.2Sn11.0Ti9.7 nanocomposite. Temperature dependence of magnetization (M-T) curves showed an increase in martensitic transformation temperatures with increasing Ti content. The Ni-Mn-Sn-Ti composite films exhibit ferromagnetic behaviour at room temperature.