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 superalloy on creep strength was investigated at 700°C. In this study, the aging time and cooling rate were changed to alter the morphology of primary and secondary precipitates. Slow furnace cooling from the aging temperature was employed to obtain a clean matrix channel completely devoid of secondary γ′ precipitates. On the other hand, the forced-air quenched specimens included numerous superfine γ′ precipitates in the matrix channel. Since secondary γ′ precipitation can significantly decrease the net width of these matrix channels irrespective of primary γ′ sizes, the effect of secondary γ′ precipitation on creep strength was much larger than that of primary γ′ precipitates size. It was revealed that the net width of the matrix channel between precipitates could better account for the morphology effect of γ′ precipitates in Ni-based superalloys.