Abstract
The Ni_2MnGa films were deposited on an alumina substrate with a radio-frequency magnetron sputtering apparatus using Ni_<50>Mn_<25>Ga_<25> and Ni_<52>Mn_<24>Ga_<24> targets. The sputtering power was 50 or 200 W. The thickness of the deposited films was about 5 μm. After deposition, the films were annealed at 873-1173 K. for 3.6 or 36 ks. The as-deposited films were crystalline and had columnar grains. After heat treatment, the grains widened and the grain boundary became indistinct with increasing heat treatment temperature. MnO and Ni_3(Mn, Ga) precipitations were observed in the heat-treated films. The mechanical properties of the films were measured by the nanoindentation method. Hardness and elastic modulus of as-deposited films were larger than that of arc-melted bulk samples. The hardness of the films was changed between 600 and 300 affected by the composition, crystal structure, microstructure and precipitation, etc. The elastic modulus of the films was also changed from 140 to 90 GPa with heat treatment conditions.
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