Effects of the amount of γ′ and oxide content on the secondary recrystallization temperature of nickel-base superalloys

Abstract

The effects of the amount of γ′ and yttria (Y2O3) content on the secondary recrystallization (SRx) temperature of as-extruded material of the mechanically alloyed nickel-base superalloys based on a superalloy TMO-2 were investigated. It was observed that (1) the primarily recrystallized grain size of the as-extruded material decreased with increasing the γ′ and the yttria content in the material; (2) the SRx temperature decreased with decreasing the yttria content and with increasing the amount of theγ′ up to about 55 vol pct, while (3) the temperature increased for the material containing more than 65 vol pctγ′; and (4) the SRx temperatures of the material containing 75 vol pctγ′ phase with 1.1 wt pct yttria and 55 vol pctγ′ phase with no yttria were identical to theirγ′ solvus. From these results, the following conclusions are drawn: (1) dissolution of theγ′ particles is a necessary, but not a sufficient, condition for the occurrence of secondary recrystallization; (2) secondary recrystallization of a material with sufficiently smaller grain size occurs at a temperature higher than theγ′ solvus and the temperature at which the yttria particles lose their ability to prevent rapid growth of the primarily recrystallized grains; and (3) the SRx temperature of a material with larger grain size depends on grain size.