Microstructure, hardness, resistivity and thermal stability of sputtered oxide films of AlCoCrCu0.5NiFe high-entropy alloy

The sputtered oxide films of AlCoCrCu0.5NiFe high-entropy alloy were deposited on the silicon wafer using radio frequency sputter system, and subsequently were annealed at 500, 700 or 900 degrees C. Surprisingly, the sputtered films are of simple structure. With no oxygen addition to the working gas, the AlCoCrCu0.5NiFe high-entropy alloy film is amorphous. When the oxygen content in the working gas is between 10 and 50%, the sputtered oxide films are HCP with lattice constants of a = 0.3583 nm and c = 0.4950 nm. Before annealing, both the resistivity and thickness of the oxide film decrease with increasing oxygen content and the hardness value reaches maximum at 30% O-2. No new phases in the oxide films form during annealing, indicating the oxide films are very stable at high temperature. However, the crystal grains tend to grow up and the micro-hole size among grains increases with the annealing temperature. The resistivity of the oxide film steps up with annealing temperature, whereas the hardness value decreases. The oxide-film thickness changes very little during annealing. (c) 2006 Elsevier B.V. All rights reserved.