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

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 (Ni-3(Al,Ti,Nb), gamma ') and delta (Ni3Nb, delta) precipitates. The solutionizing temperatures ranged between 954 to 1100 degrees C based on the solvus temperature of the gamma ' phase. The 954 degrees C solutionizing treatment resulted in incomplete dissolution of the gamma ' phase and a relatively high-volume fraction of the delta phase, which formed preferentially at grain boundaries. The gamma ' phase was completely dissolved during each of the other three solutionizing treatments (1000, 1050, and 1100 degrees C), while the fraction of the delta phase decreased with increasing solutionizing temperature. The 1100 degrees C solutionizing treatment led to significant grain growth of the matrix gamma phase. After solutionizing, the samples were subjected to a standard two-step aging treatment (788 degrees C for 8 h followed by 704 degrees C for 8 h) to see the relative effect of the solutionizing on the precipitation during aging.