THIN-SECTION SITE AND GRAIN-SIZE DEPENDENT MONKMAN-GRANT DUCTILITY OFA NICKEL-BASE SUPERALLOY

The combined effects of thin section size D and grain size d(G) (or nu mber of grains across the gauge section n(G)) on the creep behaviour o f conventionally cast MAR-M002 were studied for creep conditions of 90 0 degrees C and 300 MPa. It was observed that there was a linear corre lation between the t(R)/d(G) and epsilon(m)/D ratios on log-log scales (the modified Monkman-Grant relationship), where t(R) is the creep ru pture life and epsilon(m) is the minimum creep rate. The Monkman-Grant ductility t(R) epsilon(m) showed a rapid improvement with increasing D-2/n(G) ratio. It is concluded that the existence of the modified Mon kman-Grant relationship is due to the coupling of the creep deformatio n in the secondary region through grain boundary sliding with the cree p crack growth behaviour int he tertiary region. (C) 1997 The Institut e of Materials.