Microstructure and mechanical properties of the Inconel 718 superalloy manufactured by selective laser melting

The work is devoted to the study of the microstructure and mechanical properties of the nickel base superalloy Inconel 718 manufactured by selective laser melting (SLM). Multiple cycles of heating and cooling during SLM led to the formation of a complex microheterogeneous microstructure. The microstructure of the superalloy manufactured by SLM consisted of elongated gamma grains with a transversal size of 10 -100 mu m and a longitudinal size of 50 - 300 mu m, which in its turn consisted of columnar and equiaxed subgrains. Stable and metastable precipitates of the delta-Ni3Nb and gamma ''-Ni3Nb phases, carbides and probably oxides, were detected along the subboundaries. The standard heat treatment of the superalloy manufactured by SLM resulted in a partial dissolution of the delta phase and the metastable gamma '' phase during solid solution treatment and precipitation of the dispersed metastable gamma '' phase during ageing. The microstructure characterization performed by electron backscatter diffraction technique (EBSD analysis) revealed that the size and elongated form of the gamma grains was not changed after the heat treatment, the size of the subgrains slightly increased, the fraction of low-angle boundaries (subboundaries) decreased, and the fraction of high-angle grain boundaries increased. Tensile tests were carried out at T= 20 - 700 degrees C for the superalloy samples subjected to standard heat treatment. The tensile direction was parallel to the building direction. The tensile tests showed that the superalloy manufactured by SLM exceeded the requirements of the AMS 5662 certificate for the superalloy Inconel 718 in a hot forged condition subjected to standard heat treatment.