The effect of laser scanning path on microstructures and mechanical properties of laser solid formed nickel-base superalloy Inconel 718

Two kinds of laser scanning paths, i.e. single direction raster scanning (SDRS) and cross direction raster scanning (CDRS), were used to prepare Inconel 718 alloy parts by laser solid form (LSF) technology. The microstructures and mechanical properties of LSF Inconel 718 samples were investigated. It is shown that the as-deposited microstructure of SDRS sample is composed of columnar dendrites which grow epitaxially along the deposition direction; but in the CDRS sample, the continuous directional growth of columnar grains is inhibited and the orientation deviation of dendrites in two adjacent layers increases. The as-deposited grains of the CDRS sample are finer than those of the SDRS sample. After heat treatment, recrystallization occurs and grains of both samples are refined. However, the recrystallized grains in SDRS sample are not as uniform as that of the CDRS sample. Tensile testing at room temperature indicates that the ultimate tensile strength of these two samples is similar; however, the ductility of the CDRS sample is much better than that of the SDRS sample. Fracture surface examination presents a transgranular mode of crack propagation for the SDRS sample and a mixture of transgranular and intergranular modes of crack propagation for the CDRS sample. The inhomogeneity of grain size is considered to be the prime reason for the worse ductility of the SDRS sample.