ON THE THIN-SECTION SIZE-DEPENDENT CREEP STRENGTH OF A SINGLE-CRYSTALNICKEL-BASE SUPERALLOY

The combined effects oi thin-section size, D, and microcracks on the c reep behaviour of the single crystal MAR-M002 were investigated at the creep conditions of 300 MPa and 900 degrees C. It was observed that t he 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 me an-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 p articles (cavity density) per cross-section. The behaviour of the cree p rupture ductility was interpreted in terms of the weakest link, or ' 'largest-flaw'' concept; the observation of the higher proportion of t he less likely dangerous (smaller in size) microcracks with increasing NT was the underlining reason for the improvement in ductility.