Effect of aluminium and alumina ratio of aluminide coating on 304 stainless steel by slurry aluminizing

Abstract

Aluminide coating formed protective layer of alumina that protect from high oxidation. However, the composition of coating that determined the coating’s properties should be intensively considered. The aim of this study is to develop an aluminide coating on 304 stainless steel using low temperature aluminizing. The aluminide coating was developed using slurry aluminizing with and without alumina addition. The coating then was annealed at 650 °C for 2, 4, 6 and 8 h. The coatings were characterized for morphology, coating thickness, coating composition, phases and hardness using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray Diffraction (XRD) and Vickers microhardness. For slurry composition containing only Al and 7Al:3Al2O3, the aluminide coating successfully developed on the surface. However, for 5Al:5Al2O3 and 3Al:7Al2O3 slurry compositions, the coating produced was not properly adhered onto the substrate. Most of the surface of the substrate remained uncoated. A single layer of FeAl3 was formed at the additive layer and a thin layer of FeAl was formed at the interdiffusion zone. The addition of alumina has no effect on the type of phase formed in the coating. When alumina was added to the slurry, the coating thickness was reduced. Vickers microhardness measurements revealed that the additive layer, interdifussion zone (IDZ), and substrate have hardness in the range of 760–920 HV, 580–680 HV, and 200–230 HV, respectively.