High-temperature oxidation and hot corrosion behavior of the Cr-modified aluminide coating obtained by a Thermal Diffusion process

Abstract

An outward-grown Cr-modified aluminide coating was prepared on the nickel-based superalloy GH625 by the neutral salt bath method. High-temperature oxidation and hot corrosion experiments were carried out to investigate the high-temperature oxidation and hot corrosion resistance. The results indicate that the oxidation mass gain of Cr-modified aluminide coating is 0.413 mg cm−2, which is 56.25% lighter than that of the substrate and 25.72% lighter than the simple-aluminized coating. The Cr-modified aluminide coating has the smallest parabolic rate constant k p 1.6 × 10−3 mg2 · cm−2 · h−1. After hot corrosion, the Cr-modified aluminide coating has the lowest slope of corrosion kinetic curve. The corrosion mass gain of the Cr-modified aluminide coating is 6.7 mg cm−2, which is only 56.76% of that of the simple-aluminized coating. The XRD results show that the surface phase compositions of the Cr-modified aluminide coating after oxidation are β-NiAl, AlNi3, Cr2O3, and α-Al2O3, while the surface phase compositions after corrosion are AlNi3, Cr2O3 and α-Al2O3. According to the SEM results, there are no obvious defects on the surface after oxidation and corrosion. The cross-sectional morphologies show that the Cr-modified aluminide coating has a thicker outermost layer and diffusion zone than that of simple-aluminized coating after oxidation and corrosion. The outermost layer consisting of a large number of dark β-NiAl phase and the interdiffusion zone composed of the Cr-rich metal compound may be able to act as a barrier to slow the inward-diffusion of external oxygen and corrosive elements. All the results show that the addition of Cr in the simple-aluminized coating has a beneficial effect on the resistance of high-temperature oxidation and hot corrosion.