A comparative investigation on bi-layer Al-Cr/Al-Si coating and mono-layer Al-Cr-Si coating synthesized on Ti-6Al-4V alloy substrate by mechanical alloying method

A bi-layer Al-Cr/Al-Si coating and a mono-layer Al-Cr-Si coating were respectively produced on the Ti -6Al-4V alloy substrate by mechanical alloying method. The bi-layer coating had an inner composite Al -Si layer and an outer composite Al-Cr layer, which was obtained by milling in Al-Si powder and Al-Cr powder successively. The mono-layer coating was a S-ip and C-rp reinforced Al matrix coating. The adhesion behavior, the microhardness, the friction and wear resistance, and the high-temperature oxidation resistance of the coatings were investigated and compared. The results indicated that the mono-layer coating had better adhesion behavior compared with the outer layer of the bi-layer coating. Both the mono-layer and the bi-layer coatings could improve the surface microhardness of the substrate. The mono-layer coating had higher surface microhardness. But the bi-layer coating had an inner cushioning layer to maintain the hardness and prevent its sharp decrease with the increase of coating depth. The mono-layer coating had better friction and wear resistance. The bi-layer coating had lower mass gain and oxidation rate compared with the mono-layer coating. A continuous Al3Ti layer formed during oxidation of the bi-layer coating, which could protected the substrate effectively at the elevated temperature. The mono-layer coating was severely oxidized and porous structure formed in the coating. The bi-layer coating had advantages in protecting the substrate at elevated temperature. (C) 2017 Elsevier B.V. All rights reserved.