On the thin-section size dependent creep strength of a single crystal nickel-base superalloy

Abstract

The combined effects oi thin-section size, D, and microcracks on the creep behaviour of the single crystal MAR-M002 were investigated at the creep conditions of 300 MPa and 900 degrees C. It was observed that the creep rupture life, t(R) is controlled by the mean microcrack size to thin-section size, (d(c)/D), (or the total number, (N-m), of the mean-sized microcrack particles across the diameter, assuming D/d(c) = N-m); reducing N-m continuously improves t(R). The creep rupture strain (or ductility), epsilon(R), can be improved sharply by increasing the total number, N-T, of microcrack particles across the cross-section, N-T proportional to (DNA)-N-2, where N-A is the number of microcrack particles (cavity density) per cross-section. The behaviour of the creep rupture ductility was interpreted in terms of the weakest link, or ''largest-flaw'' concept; the observation of the higher proportion of the less likely dangerous (smaller in size) microcracks with increasing NT was the underlining reason for the improvement in ductility.