Microchemical inhomogeneity in a highly alloyed nickel alloy

1. Extruded rods of alloy EP975ID, which have an elongation value of δ<35% at 1180°C, as a rule, characteristically have a high degree of dendritic segregation of Al, Ti, and W which arose from the ingot. In addition, in the rods obtained from a number of heats there were large segregation spots which were accumulations of large γ′-phase particles, W, Cr, and Mo based borides, and Nb, Ti, and B-based carbides. In the spots there is a high degree of concentration variance between the dendritic cells and the interdendritic space (large γ′-phase precipitates) in comparison to what is found in the matrix. 2. A homogenization anneal of the ingots leads to a decrease in the microchemical inhomogeneity. Under these conditions the tungsten, which diffuses to the interaxial spaces, enriches the eutectic γ′-γ′-phase precipitates. This, in turn, can lead to the formation of localized accumulations of carbides and borides during subsequent treatment. 3. The main reason that quench cracks form in stampings made of alloy EP975ID is, evidently, due to chemical inhomogeneity caused by segregation of the alloying elements. These inhomogeneities are not removed during the homogenization treatment of the ingots or during quench treatments. Quench cracks also form due to the formation of relatively large eutectic γ′-phase precipitates, micropores, and accumulations of tungsten based borides and carbides.