The effects of solutionizing and aging temperature on the microstructure of Allvac 718Plus

A study on the microstructural evolution of a Ni-based superalloy, Allvac 7l8Plus, 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 (NbNb, 5) phase precipitates. The solutionizing temperatures ranged between 945°C to 1100°C. After solutionizing, the samples were subjected to a standard two-step aging treatment (788°C for 8h followed by 704°C for 8h). The 954°C solutionizing treatment resulted in incomplete dissolution of the γ' phase and a relatively high volume fraction of the 5 phase, which formed preferentially at grain boundaries. The γ' phase was completely dissolved during each of the other three solutionizing treatments (1000°C, 1050°C, and 1100°C), while the fraction of the 8 phase decreased with increasing solutionizing temperature. The 1100°C solutionizing treatment led to significant growth of the matrix grains (Ni (FCC), γ).