Microstructure evaluation of si-modified aluminide coatings on in625 deposited by slurry aluminizing process

Abstract

Si-modified aluminide coatings are promising for improving oxidation and corrosion resistance in superalloys at high temperatures. This study investigated the effect of different silicon levels in the aluminizing slurry on the morphology and structure of Si-modified aluminide coatings on IN625. This process involved spraying a slurry of aluminum and silicon particles in an aqueous PVA solution onto IN625 samples, followed by heat treatment under controlled conditions - two atmospheres (air and argon) and two heating ramps (regular and flash). Surface morphologies, cross-sectional structures, elemental compositions, and phase formations were analyzed using FE-SEM, SEM, EDS, and XRD methods, while DTA analysis assessed AlSi alloy formation during heating. The results showed that higher silicon content in the slurry increased silicon incorporation in the coatings but did not reduce aluminum activity enough to deposit a low-activity aluminide coating. The inert atmosphere (argon) and flash heating promoted the co-deposition of Si and Al, resulting in Cr and Mo silicide-enriched outer layers in some samples. The aluminum content in all slurries was sufficient for consistent β-NiAl formation across different silicon levels. The average silicon content in coatings ranged from 5 to 15 wt% and depended on the slurry composition and heat treatment conditions. The Al30Si slurry produced the thickest coatings (~90 μm), with further increases in Si leading to reduced thickness. This study suggests that slurry aluminizing can be optimized to control silicon incorporation, depositing Si-modified aluminide coatings for durable, high-performance applications.