EFFECTS OF TEMPERATURE AND AL-CONCENTRATION ON FORMATION MECHANISM OF AN ALUMINIDE COATING APPLIED ON SUPER ALLOY IN۷۳۸LC THROUGH A SINGLE-STEP HIGH ACTIVITYGAS DIFFUSION PROCESS

Abstract: activity gas diffusion process has been investigated in this research. Effects of coating temperature and aluminumconcentration in powder mixture on formation mechanism were studied using optical and scanning electronmicroscopes, EDS and X-ray diffraction (XRD) techniques. For this purpose two different packs containing ۱ and ۲wt% aluminum powder, were used for coating the samples at two temperatures, ۸۵۰ºC and ۱۰۵۰ºC. The ratio of Al toactivator was kept constant in both packs. By increasing the Al content in high activity powder mixture, theconcentration of diffused Al increased in the coating layers, and the thickness of coating increased. At ۱۰۵۰ºC as therate of diffused Al to the interdiffusion zone increased, this zone gradually transformed to outer coating phases. At۸۵۰ºC coating formed by inward diffusion of Al, but at ۱۰۵۰ºC it was initially formed by inward diffusion of Al followedby outward diffusion of Ni.Formation mechanism of an aluminide coating on a nickel base superalloy IN۷۳۸LC via a single step high