Effect of heat treatment on the microstructure and elevated temperature tensile properties of Rene 41 alloy produced by laser powder bed fusion

Abstract

The microstructure and elevated temperature mechanical properties of a precipitation hardenable Nickel based superalloy, Rene 41, fabricated by laser powder bed fusion followed by two different heat treatment regimes were studied. The as-built (AB) microstructure consists of γ columnar grains aligned in <100> direction. No γ′ precipitates were observed in the AB condition. Following to a sub-solvus solutionizing and aging heat treatment, the AB grain morphology was maintained. The development of fine γ′ precipitates within the grains along with the discrete carbide particles on the grain boundaries occurred. Heat treatment above the solvus temperature of γ’ resulted in the formation of a random equiaxed grain morphology. The γ′ and carbide precipitation was also observed in this heat treatment regime, but their distribution and morphology were different. Uniaxial tensile tests were conducted at 760 °C. Average yield strength values for AB, sub-solvus and super-solvus heat treated alloys were 879, 824 and 855 MPa respectively. The three tested conditions showed similar strength values that are comparable with a wrought alloy at the testing temperature. However, the elongation and deformation behaviors were different for each condition. Sub-solvus heat treatment lead to the highest elongation at break with 22% whereas super-solvus heat treatment resulted in the highest work hardening rate during deformation.