The Effects of Solutionizing Temperature on the Microstructure of Allvac 718Plus

Abstract

A study of the microstructural evolution of a Ni-based superalloy, Allvac 718Plus, in the forged condition, was performed by varying the solutionizing temperature. Different solutionizing temperatures were chosen to obtain different fractions of the gamma prime (Ni3(Al,Ti,Nb), γ′) and delta (Ni3Nb, δ) precipitates. The solutionizing temperatures ranged between 954 to 1100 °C based on the solvus temperature of the γ′ phase. The 954 °C solutionizing treatment resulted in incomplete dissolution of the γ′ phase and a relatively high-volume fraction of the δ phase, which formed preferentially at grain boundaries. The γ′ phase was completely dissolved during each of the other three solutionizing treatments (1000, 1050, and 1100 °C), while the fraction of the δ phase decreased with increasing solutionizing temperature. The 1100 °C solutionizing treatment led to significant grain growth of the matrix γ phase. After solutionizing, the samples were subjected to a standard two-step aging treatment (788 °C for 8 h followed by 704 °C for 8 h) to see the relative effect of the solutionizing on the precipitation during aging.