THE CYCLIC-OXIDATION BEHAVIOR OF SEVERAL NICKEL-BASE SINGLE-CRYSTAL SUPERALLOYS WITHOUT AND WITH 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 cyclic-oxidation resistance in air at 1000 and 1150-degrees-C The investigations also included two materials (CMSX-6, SRR 99) with an RT-22 coating. Weight changes and acoustic emission were recorded up to 1000 cycles and scales, coatings, and substrates were characterized by metallography, SEM, and microprobe in postexperimental investigations. The best cyclic-oxidation behavior and excellent resistance to spalling even at 1150-degrees-C were shown by a laboratory version of CMSX-4 containing between 10 and 60 ppm Y. While at 1000-degrees-C interdiffusion can be taken as tolerable for the coated alloys, there is rapid degradation of the coating by interdiffusion at 1150-degrees-C.