INVESTIGATION OF BONDING MECHANISM BETWEEN PLASMA SPRAYED Al{sub}2O{sub}3 TOP COATING AND Ti-Al UNDERCOATING ON STEEL SUBSTRATE

摘要

Bonding mechanism of plasma sprayed Al{sub}2O{sub}3 top coating onto Ti-Al undercoating made with Ti and Al mixed powders on mild steel substrate was investigated by measuring adhesive strength and observing fractured surfaces of the dual coating system in comparison with single phase undercoatings of Ti or Al. The Ti-Al coating consisted of Al phase and Ti compound phases, but its surface layer was composed mainly of Al splats covered with thin oxide layer of Al{sub}2O. The Al{sub}2O{sub}3 top coating would bond to the Ti-Al undercoating by mechanical anchoring effect.