Effect of Solution Treatment on High-Temperature Mechanical Properties of IN718 Manufactured by Selective Laser Melting

The microstructure observation, hardness test, texture analysis, and axial tensile test were conducted to clarify the effect of special solution treatment (at 980 °C for 1 hour with air cooling) on high-temperature mechanical properties of Inconel 718 (IN718) superalloy manufactured by selective laser melting (SLM). After solution treatment, the columnar and equiaxed grains with a diameter of 300 nm dissolved, which were formed due to the high cooling rate during the SLM procedure. Moreover, the strengthening γ′′ or δ phases precipitated at grain boundaries after solution treatment resulting in the increment of mechanical properties. Results of electron backscatter diffraction show that the solution treatment has a little effect on the texture, but can increase the fraction of high angle grain boundaries and Schmid factor by 15.6% and 1.5%, receptively. Varieties of mechanical properties at room and high temperature were explained with the characteristics of low-angle grain boundary, Schmidt factors, and grain size. Fractographic features analysis was used to reveal the high temperature deformation behavior, meanwhile, the stress-strain curves were fitted based on the Ramberg-Osgood equation. The differences between the tensile test fracture surfaces indicate that the solution treatment can change the shear strength limit of SLM IN718 superalloy.