Preparation of layered a-Al^sub 2^O^sub 3^/TiO^sub 2^ composite coating by pack cementation process and subsequent thermochemical treatment

• Published in: Surface & coatings technology 2017-12, Vol.330, p.277
• Main Authors: Wang, Yan, Feng, Shuaijie, Liu, Dawei, Zhang, Cheng, Xu, Juexin, Luo, Chunlan, Suo, Jinping
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Oxidation; Pack cementation; Pretreatment; Protective coatings; Scale (corrosion); Thickness; Titanium; Titanium oxides
• ISSN: 0257-8972; 1879-3347

An Al-Ti coating deposited by pack cementation technique was subjected to the thermochemical treatment. The Al-Ti coating consisted of an outer AlTi-rich layer and an inner transition layer. After the direct oxidation treatment, the coating surface was covered by many particle agglomerations and the scale was porous. A 10 µm thick oxide layer, which consisted of an outer TiO2 dominated layer and an inner α-Al2O3 dominated layer, had grown on top of the coating. The multilayer structure of this coating was "TiO2/α-Al2O3/transition layer". 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.