Effects of heat treatment on microstructure and mechanical properties of Inconel 625 alloy fabricated by wire arc additive manufacturing process
(Department of Materials Engineering, Faculty of Engineering, University of Sistan and Baluchestan, P. O. Box 98135-674, Zahedan, Iran)
Abstract: The microstructure and mechanical properties of Inconel 625 alloy fabricated by wire arc additive manufacturing process were evaluated under as-prepared and heat-treated conditions. A dendritic Ni-based solid solution phase along with (Nb,Ti)C carbide, Laves, and δ-Ni3Nb secondary phases were developed in the microstructure of the as-prepared alloy. Solution heat treatment led to the dissolution of Laves and Ni3Nb phases. In addition, dendrites were replaced with large columnar grains. Aging heat treatment resulted in the formation of grain boundary M23C6 carbide and nanometric γ'''''''' precipitates. Hardness, yield and tensile strengths, as well as elongation of the as-prepared part, were close to those of the cast alloy and its fracture occurred in a transgranular ductile mode. Solution heat treatment improved hardness and yield strength and declined the elongation, but it did not have a considerable impact on the tensile strength. Furthermore, aging heat treatment caused the tensile properties to deteriorate and changed the fracture to a mixture of transgranular ductile and intergranular brittle mode.
Key words: nickel alloys; additive manufacturing; direct energy deposition; heat treatment; microstructure