An investigation of the microstructural evolution and tensile properties of a nickel-based GH648 superalloy manufactured through selective laser melting

In this study, a nickel-based GH648 superalloy, with a high Cr content up to similar to 35 wt%, was manufactured through selective laser melting (SLM) in argon atmosphere. The SLMed GH648 superalloy possesses excellent tensile properties, with a yield strength of 890 MPa and a tensile ductility of similar to 40%. Microstructures of the SLMed GH648 superalloy were studied by SEM, TEM, optical microscopy and X-ray diffraction. Both the EBSD and XRD results indicate that the alloy possesses a strong [220] texture paralleling to the Z axis and a strong [002] texture paralleling to the Y axis. In the SLMed GH648 superalloy, austenite gamma (Ni-Cr) matrix and alpha-Cr phase are predominated, with the alpha-Cr phase being precipitated mainly in the intercellular regions where Cr, Nb, Al and Ti elements are preferentially segregated. The spacing (lambda(1)) of the primary dendrite arm ranges from 0.35 mu m from the bottom of the molten pool to over 0.73 mu m at the top of the molten pool. The temperature gradient of similar to 1.03 x 10(7) K/m of solid/liquid interface is also calculated by measuring the width of the partially melted zone. The orientation relationship between the alpha-Cr and the gamma matrix was tested to be (110)[001](alpha)//(111)[011](gamma). Both the coherent alpha-Cr phase and particular microstructures, including strong texture, gradient cellular solidification microstructures, high dislocation density and subgrain boundaries, contribute to the superior tensile properties of the superalloy. At varied stages of solidification, the convection and liquid flow in molten pool control the micro-segregation degree of Cr element in the SLM manufacturing process.