Hardness of sputter deposited nanocrystalline Ni3Al thin films

Nanocrystalline thin films of nominal composition Ni-25 at.% Al have been sputter deposited from a target of the intermetallic compound Ni₃Al using different sputtering conditions. Increase in the pressure of sputtering gas resulted in a substantial reduction in the grain size of these nanocrystalline films and a consequent enhancement in their hardness. While films deposited onto heated substrates exhibited larger grain sizes as compared to those deposited on unheated substrates at the same sputtering pressure, the hardness of the former films was substantially higher. The reason for this enhanced hardness is the long-range chemical ordering in films deposited on heated substrates and the formation of L1₂-Ni₃Al, the thermodynamically stable phase for this composition.