The conditions for depositing hard aluminum oxide film of a Knoop hardness number over 2000 have been investigated by an activated reactive evaporation process.
In this experiment, pure aluminum was evaporated in a reduced oxygen atmosphere and an aluminum oxide film was deposited on the substrates of mild steel or glass. With increases in ionization current, the hardness of the deposited film increased from HK 200 to HK 3600 and the rate of deposition decreased from 4.7×10-3μm/s to 0.33×10-3μm/s. Hardness increased abruptly to HK 2700 in reduced oxygen atmospheres over 9.31×10-3Pa and reached HK 3600 at a pressure of 13.3×10-3Pa, wheareas it decreased to HK 1200 at a pressure of 16.0×10-3Pa.
Hardness also increased from HK 1700 to HK 3000 when a bias voltag of 0.1-0.2kV was applied to the substrate, and reached HK 3600 at a bias substrare voltage of 0.4kV. Up to 589K, hardness was not influenced by the pre-heating temperature of the substrate but increased from HK 1800 to HK 3600 under pre-heating at 713K-793K. Typical conditions for depositing aluminum oxide film of over HK 2000 were electron beam gun power of 10kV-500 or 550mA, ionization current over 15A, oxygen pressure of 9.31-10.3×10-3Pa, substrate pre-heating temperature above 793K and a bias substrate voltage above 0.2kV.
