Microstructural Evolution and Room Temperature Mechanical Properties of Additively Manufactured XH67 Nickel-Based Superalloy

A new high strength nickel-based superalloyNickel-based superalloy, XH67, has been fabricated by the laser powder bed fusionLaser Powder Bed Fusion (LPBF) process (LPBFLaser Powder Bed Fusion (LPBF)). Novel heat treatmentsHeat treatment via direct aging, solutionizing and aging, were carried out and compared with the as-printed alloy, to study the evolution of phase equilibria and bring out the optimum mechanical propertiesMechanical properties of high strength and good ductility. A γ′ strengthened alloy, XH67 shows a high strength of ~1040 MPa with a 25% ductility, after direct aging (γ′ size of 10–30 nm and a volume fraction of 25–30%). The as-printed structure with a cellular-dentritic morphology was retained during direct aging heat treatmentHeat treatment contributing to the strength by Hall–Petch strengthening along with precipitationPrecipitation hardening by γʹ precipitatesPrecipitates. Discontinuous precipitationDiscontinuous precipitation along the cell boundaries was a unique microstructural feature that are observed in the present alloy. Annealing twins were seen after solution and aging along with coarseningCoarsening of the γ′ precipitatesPrecipitates up to 50 nm. Thermodynamic calculation (Thermo-Calc) was used to validate the observed phase evolution as a function of heat treatmentHeat treatment.