The Mechanical Processes of Thermal Fatigue Degradation in in-100 Superalloy

Abstract

The effect of thermal fatigue history on the surface degradation of IN-100 nickel-base alloy was examined employing double-edge wedge specimens and a special induction heating procedure. The respectives stress-strain histories, as determined from thermo-elasto-plastic finite element analyses, are presented. Depending upon strain history, two modes of surface degradation were observed: scalloping and through-thickness cracking of a uniform oxide layer. The degree of scalloping was shown to depend on the magnitude of compressive strain at the surface. Severe scalloping was observed after 3000 thermal cycles between peak strains of −0.48% at 1050° C and +0.08% at 400° C. More than 3000 cycles between peak strains of −0.24% at 1050° C and 0.23% at 400° C did not produced scalloping. The number of cycle to crack initiation was found to correlate with peak compressive strain. The findings are shown to be consistent with a mechanism for scallop initiation and growth involving cyclic oxide cracking and cyclic ratchetting. The implementation of the results in the operating and lifing procedures of commercial aircraft engines parts is discussed.