Nanocrystalline γ-Al2O3 thin film deposited by magnetron sputtering (MS) at low temperature

An Al2O3coating was deposited onto polished square pieces of 304L stainless steel substrates using magnetron sputtering (MS) technique. Before deposition, etching by argon plasma was performed to clean the metal surface, while deposition parameters were controlled. The patterns of the MS Al2O3 films grown at 150°C correspond to the tetragonal γ-Al2O3 polycrystalline structure, with lattice parameters a = b = 0.57 nm and c = 0.79 nm. The hardness value for the film is found to be 12.1 GPa, and hardness increased from 7 GPa for amorphous to about 20 GPa for fully crystallized Al2O3. Scanning Electron Microscopy (SEM) photographs taken after the wear test to show a typical worn surface, where delaminating of the Al2O3 layer is found to be the main failure mode.