Study on factors affecting high temperature anisotropic stress rupture properties of SLM-IN718 alloy

IN718 components often need to be used in high temperature complex stress environment for a long time. High temperature stress rupture and anisotropy are important performance indexes. In order to study the influence factors on the lasting anisotropy of Selective Laser Melting (SLM) forming IN718, the printing state was treated by solution aging (SA) and direct aging (DA) respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) were used to characterize the phase, microstructure and texture of XY and YZ plane of the samples in two states. The stress rupture of the horizontal/vertical samples in two states was tested at 690 MPa and 650 ℃. After the test, the fracture and section crack were characterized and quantified. The results show that the printed microstructure of DA samples is maintained to a large extent, and there are obvious molten pool traces. The grain size hardly changes. The microstructure shows a large amount of segregation, and XRD shows a slight peak of MC phase. The grain size and distribution of SA samples are similar to that of DA samples, and there is a large range of δ phase precipitation. The difference of high temperature stress rupture between horizontal/vertical specimens decreases with the decrease of the number of crack initiation points. The difference of molten pool structure and grain boundary structure perpendicular to the stress loading axis is the key factor affecting its stress rupture anisotropy at high temperature.