THE ISOTHERMAL-OXIDATION BEHAVIOR OF SEVERAL NICKEL-BASE SINGLE-CRYSTAL SUPERALLOYS WITH AND WITHOUT COATINGS

Several commercial single-crystal superalloys (CMSX-2, CMSX-3, CMSX-4, CMSX-6, SRR 99) and some laboratory versions of one of them (CMSX-4) with various Y-additions were investigated concerning their oxidation resistance in air at temperatures between 800 and 1200-degrees-C The investigations also included two materials (CMSX-6, SRR 99) with an RT-22 coating. Weight change was recorded for times of up to 1000 hr (in some cases up to 1600 hr). Oxidized coatings and substrates were characterized by metallography, SEM, and microprobe analysis. Most of the alloys showed good oxidation resistance up to 1000-degrees-C, while there was complete spalling during cooling after oxidation at 1150-degrees-C and 1200-degrees-C for the uncoated and Y-free alloys. Coated alloys were superior, however the best behavior was shown by a laboratory version of CMSX-4 containing between 10 and 60 ppm Y. Interdiffusion at 1000-degrees-C is tolerable for the coated alloys, but there was extremely rapid degradation of the coating by interdiffusion at 1200-degrees-C.