Effect of Substrate Roughness on Oxidation Resistance of an Aluminized Ni-Base Superalloy

TL;DR

This study demonstrates that surface preparation, especially grit blasting, significantly influences the oxidation resistance of aluminized Ni-based superalloys, affecting coating thickness, diffusion zones, and thermal shock performance.

Contribution

It reveals the impact of grit blasting on oxidation resistance and coating characteristics of aluminized Ni-based superalloys, highlighting the importance of surface preparation methods.

Findings

Grit blasting negatively affects oxidation resistance during thermal shocks.

Grit blasted IN 625 forms a thicker NiAl coating than unblasted.

Grit blasted IN 738 shows no change in coating thickness but has a thicker interdiffusion zone.

Abstract

In the present work, it is shown that the surface preparation method used on two Ni-based superalloys prior to aluminizing chemical vapor deposition (CVD) is one of the most important factors determining the oxidation resistance of aluminized Ni-based superalloys. It was found that grit blasting the substrate surface negatively affects the oxidation resistance of the aluminized coatings. For grit blasted and aluminized IN 625, a thicker outer NiAl coating was formed compared to that of IN 738. In contrast, no effect on NiAl coating thickness was found for grit blasted and aluminized IN 738. However, a thicker interdiffusion zone (IDZ) was observed. It was shown that the systems with grit-blasted surfaces reveal worse oxidation resistance during thermal shock tests, namely, a higher mass loss was observed for both grit blasted and aluminized alloys, as compared to ground and aluminized alloys. A possible reason for this effect of remaining alumina particles originating from surface grit blasting on the diffusion processes and stress distribution at the coating/substrate is proposed.