Creep, Fatigue and Their Interaction in Coated and Uncoated Rene 80

摘要

The effects of coating and creep-fatigue interactions on the turbine blade material Rene 80 at 900 C were investigated. Coating reduces high cycle fatigue life because of crack initiation at brittle particles in the coating. This process plays no role for creep, where crack initiation occurs at carbides in the base metal. Coating affects creep properties by changes of the loadbearing cross section: initially the coating increases this cross section and consequently the minimum creep rate decreases. However, after exhaustion of the coating ductility, coating cracks reduce the load bearing area and thereby reduce the creep rupture life. For coated and uncoated Rene 80 short prior creep times increase subsequent fatigue life since the interfacial dislocation network around the cuboidal gamma prime precipitates densify during creep. Long prior creep times are unfavororable because of coarsening of the gamma prime spheroids. Prior fatigue has little influence on creep rupture life since the dislocations introduced during fatigue are annealed out during creep.