Effect of primary and secondary precipitates on creep strength of Ni-base superalloy single crystals

The influence of primary and secondary precipitates in a single-crystal sup eralloy on creep strength was investigated at 700 degrees C. In this study, the aging time and cooling rate were changed to alter the morphology of pr imary and secondary precipitates. Slow furnace cooling from the aging tempe rature was employed to obtain a clean matrix channel completely devoid of s econdary gamma' precipitates. On the other hand, the forced-air quenched sp ecimens included numerous superfine gamma' precipitates in the matrix chann el. Since secondary gamma' precipitation can significantly decrease the net width of these matrix channels irrespective of primary gamma' sizes, the e ffect of secondary gamma' precipitation on creep strength was much larger t han that of primary gamma' precipitates size. It was revealed that the net width of the matrix channel between precipitates could better account for t he morphology effect of gamma' precipitates in Ni-based superalloys. (C) 20 00 Elsevier Science S.A. All rights reserved.