The mechanical properties of thin alumina film deposited by metal-organic chemical vapour deposition

Amorphous alumina films were deposited by metal-organic chemical vapour deposition (MOCVD) on stainless steel, type AISI 304. The MOCVD experiments were performed in nitrogen at low and atmospheric pressures. The effects of deposition temperature, growth rate and film thickness on the mechanical properties have been studied. The experiments were performed with the dynamic ultra-micro-hardness tester, DUH-200, and the scanning scratch tester, SST-101, both developed by Shimadzu. The DUH-200 is associated with crack formation during indentation. This technique involves a qualitative method to study the crack behaviour of the thin alumina films as well as a method to estimate the fracture toughness of the film and the film/substrate interface. The experiments performed with the SST-101 are based on the estimation of the film adhesion to the substrate by determining a critical load; the load where the film starts to spall or to delaminate. The best mechanical properties were obtained using low deposition rates and high deposition temperatures. Therefore, low-pressure MOCVD is recommended in addition to the deposition of alumina films at high temperatures.