Destructive Effect of Water Vapour on an In Situ Diffusion Barrier Layer within an Aluminide Coating on IN738 Alloy

Abstract

High-temperature interdiffusion within a hot-dipped aluminide (Al-10 wt.% Si) coating on an IN738 superalloy was investigated at 1050 • C in air and in air plus water vapour. The resulting morphology of in situ diffusion barrier layer (DBL) within the aluminide coating is affected by oxidizing atmospheres; DBL can effectively retard the interdiffusion of aluminium within the coating. The location of the in situ DBL is governed by the partial pressure of oxygen at different depths from the oxide scales in both atmospheres. Meanwhile, the diffusion fluxes of different elements led to DBLs with different morphologies in the aluminide coating on the Ni-based alloy. growth and temperature of the DBL (intermetallic layer) that was formed in Pd/Cu and Pd/Ag porous stainless steel, the DBL formed by the oxidation of the substrate at 430 • C, and the DBL was effective in reducing the intermetallic diffusion at 500 • C. Müller et al. [24] discussed the effects of reactive element oxides and the property of diffusion on a self-forming DBL on nickel-based superalloys, and the DBL was destroyed due to the reaction of Y and Hf from MCrAlY (M = Ni, Co). The above studies indicated that the relationships between the growth, temperatures and reactive element oxides of the DBL, as well as its oxidation resistance, are complex and not yet fully understood at high temperature. Therefore, many factors affect the growth and morphology of the DBL. The relationship between the growth of the DBL and diffusion of elements in different atmospheres requires further study.The purpose of this research was to understand the influence between the in situ DBL and the diffusion of elements during exposure to air and air plus water vapour environment. Moreover, the relationship between the external environment and the growth of DBL has been examined. Coatings 2018, 8, x FOR PEER REVIEW 10 of 11 Author Contributions: Conceptualization, C.L. and P.S.; Methodology, J.L.; Software, X.H.; Validation, K.C., X.Y. and P.S.; Formal Analysis, X.H., K.C. and X.Y.; Investigation, C.L.; Resources, P.S.; Data Curation, J.L.; Writing-Original Draft Preparation, C.L.; Writing-Review & Editing, C.L. and P.S.; Visualization, K.C.; Supervision, P.S. and J.L.; Project Administration, P.S.