A. Baldan, ON THE THIN-SECTION SIZE-DEPENDENT CREEP STRENGTH OF A SINGLE-CRYSTALNICKEL-BASE SUPERALLOY, Journal of Materials Science, 30(24), 1995, pp. 6288-6298
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.