Preparation of layered α-Al2O3/TiO2 composite coating by pack cementation process and subsequent thermochemical treatment

In order to prepare a better α-Al2O3/TiO2 composite coating, nitridation pretreatment was added before oxidation treatment. The surface of resulting coating was compact and had no obvious particle agglomerations. The outer oxide layer, with a thickness of approximately 4 μm, exhibited a bilayer structure with an outer α-Al2O3 dominated layer and an inner TiO2 dominated layer. The multilayer structure of this coating was “α-Al2O3/TiO2/transition layer”. Beneath the oxide scale, a thin and continuous nitride layer was present, slowing down oxygen transport into the coating significantly. The oxidation behavior of Al-Ti coating changed with the nitridation pretreatment, and a better α-Al2O3/TiO2 composite coating was obtained.