Effect of Heat Treatment Temperature on Microstructure, Tensile Properties and -Precipitate Phase in Ni-based Superalloy

Here, we investigated the influence of 8 -precipitate (orthorhombic D0a Ni3Nb-ordered phase) on the room- and high -temperature tensile properties in wrought nickel -based Inconel 625 superalloys subjected to solution and aging heat treatment. Typically, solution heat -treatment temperatures in these alloys affect the solid-state precipitation of 8 -phase, which governs high -temperature tensile properties. While precipitation of fine D0a 8 -phase is known to have beneficial effects on the mechanical properties owing to the retardation of grain coarsening, Widmanstatten 8 precipitation plays a deleterious influence on the fracture toughness, tensile ductility, and fatigue resistance. Therefore, to enhance the mechanical properties of this alloy series, it is key to generate a high number density of fine D0a 8 precipitate by adjusting solid solution treatment temperatures. In this study, solution heat treatments were conducted above and below 8 -phase solvus temperatures. By applying solution heat treatment at 900 degrees C and 970 degrees C, this alloy was confirmed to have a Widmanstatten 8 phase and is composed similarly to the annealed microstructure. This Widmanstatten 8 precipitate was densely distributed at both intergranular and intragranular grains. On the other hand, when solution treatment was applied at 1040 and 1100 degrees C, more coarse particles (approximately 30 mu m) with a significant reduction of Widmanstatten type 8 phase were obtained. We found that grain size and Widmanstatten 8 -phases have an important role in the high -temperature tensile properties of Inconel 625 superalloy series.