MICROSTRUCTURAL AND DAMAGE EVOLUTION DURING CREEP OF A SINGLE-CRYSTALNICKEL-BASE SUPERALLOY

A single crystal nickel base superalloy with 0.5 atomic percent rheniu m has been investigated for its creep and stress rupture behaviour at temperatures in the range of 1033-1373 K and in the stress range betwe en 120 MPa and 1100 MPa. Rafting of gamma prime phase and its coarseni ng occurred during creep above 1173 K in the direction normal to the a pplied stress. There is evidence that cavities formed at the micropore s in the interdendritic regions, and their growth occurred along the g amma-gamma' interface in the direction normal to the applied stress. F inal failure of the specimen occurred through the interlinkage of thes e cavities. Tantalum rich phase precipitated during creep at 1323 K. T his phase was not observed in the specimens tested at and below 1223.