Mechanism of Al-Si codeposition on In738LC through single-step diffusion process

Abstract

The out-of-pack cementation method was applied to coat the Nickel-based super alloy IN738LC with Si-modified aluminide. Different mixtures of the pack containing pure Al, Si, alumina powders as an inert filler, and NH4Cl as a halide salt activator were used for co-deposition at 950 and 1,050°C. The results showed although the amount of subhalide vapour pressures of Al and Si were equal at 1,050°C, Al atoms diffused only after Si atoms had been deposited. Before heat treatment, the coating thickness formed by the pack containing 2.3 wt.% Al was 6 µm more than that containing 3.5 wt.‰ Al. After heat treatment, thickening coatings formed within the pack containing 2.3 wt.% Al was less than that obtained in the other pack containing 3.5 wt.% Al. This study suggests that increasing the depositing temperature will increase the thickness at a constant composition of the pack powder.