The precipitation of η phase during the solution treatments of Allvac 718Plus

The precipitation of eta phase during the solution treatments of Allvac 718Plus was investigated in this study. The results showed that there was free-gamma ' zone appearing around eta phase which was consistent with the hexagonal eta-Ni3(Al/Ti)0.5Nb0.5 after heat treatments. The granular eta phase was found to be the transition of the plate-like eta phase and have no pinning effect against the grain boundary, while the plate-like eta phase has a pinning effect on the grain boundary and leads to the formation of serrated grain boundaries. With the solution temperature increasing, the size and fraction of eta phase were observed to increase and then decrease with the morphology changing from granular to plate-like and then to granular. With the solution time prolonging, the fraction and size of eta phase were increased, and the eta phase formed in a cellular mode and then grow in a Widmansta center dot tten morphology into the grain with its morphology changing from the dominant granular/plate-like to Widmansta center dot ttan structure. It was found that the increase in room temperature microhardness with the solution time changing from 6 h to 24 h was caused by the formation of Widmansta center dot tten eta phase.