INTERDIFFUSION BETWEEN THE PLATINUM-MODIFIED ALUMINIDE COATING RT-22 AND NICKEL-BASED SINGLE-CRYSTAL SUPERALLOYS AT 1000-DEGREES-C AND 1200-DEGREES-C

The interdiffusion between the Pt-modified aluminide coating RT 22 and the single-crystal superalloys CMSX-6 and SRR 99 has been investigate d at 1000 and 1200-degrees-C up to 1600 h of exposure time in air and vacuum. Both coating/substrate systems possess remarkable ability at 1 000-degrees-C, in air as well as in vacuum. It appears that the plate- like precipitates of intermetallics in the interdiffusion zone between coating and substrate act as a barrier layer for interdiffusion. Some inward diffusion of Pt and Al and outward diffusion of Ti occur at 10 00-degrees-C. Rapid degradation of the coating takes place at 1200-deg rees-C mainly by interdiffusion. The Al diffusion into the substrates leads to conversion of beta-NiAl into gamma'-Ni3Al and finally into ga mma-phase. Ti rapidly diffuses outwards and becomes incorporated into the scale rich in Al. Thus, the Ti content of the substrate affects th e scaling behaviour of the coating. The intermetallic precipitates are dissolved and, therefore, so is the interdiffusion barrier. The somew hat better behaviour of the RT 22/SRR 99 system is probably caused by the greater stability of the W-rich intermetallics in this system.