Adhesion and Thermal Shock Resistance of Al₂O₃ Thin Films Deposited by PACVD for Die Protection in Semi‐solid Processing of Steel

Abstract

In this work thin Al 2 O 3 films were deposited on hot working steel AISI H11 by plasma assisted chemical vapour deposition (PACVD). The effect of the AlCl 3 /O 2 ratio in the gas mixture and the substrate temperature on the film hardness and constitution of the deposited films was investigated by nanoindentation and X‐ray diffraction, respectively. Within the investigated process parameter window thin films containing either the γ‐Al 2 O 3 or the α‐Al 2 O 3 phase were grown. The performance of these Al 2 O 3 coatings for the semi‐solid processing of steel was studied with respect to hardness, adhesion and resistance to thermal shock. The maximum critical load of 50 N as determined by scratch testing was achieved after plasma nitriding of the substrate. No cohesive or adhesive coating failure could be detected after 1000 thermal shock cycles at a contact temperature of 1170±30 °C. Based on the here presented adhesion and thermal shock data it can be concluded that the Al 2 O 3 thin films are suitable candidates for the die protection during semi‐solid processing of steel.