Influence of cooling rate during the heat treatment process on the precipitates and ductility behavior of inconel 718 superalloy fabricated by selective laser melting

IN718 superalloy by elective laser melting (SLM) has shown great application prospects in the aerospace engine key parts. Different phases are precipitated during the SLM forming process. Although the Laves phase could be dissolved in dendrites by heat treatment, the specific evolution of the second phase particles is still unclear. In this work, the influences of solution and aging heat treatment, as well as cooling rate on the precipitates and ductility behavior of IN718 superalloy fabricated by SLM were systematically investigated. The medium temperature (980 degrees C) solution treatment regimes included three different colling rates and the control group only underwent aging treatment were studied. The results indicated that high temperature solid solution treatment effectively improved compositional segregation and significantly enhanced homogeneity of microstructure. The reduce of cooling rate at 980 degrees C was beneficial to the extension time and increased the number of delta phase precipitation. An appropriate number of delta phase improves the notch sensitivity and nails grain boundaries. In addition, the complex dislocations and second phase particles retards the migration of slip dislocations during ductility deformation process, which enhances the strength of SLM-ed IN718. The yield strength of specimens increases from 680 MPa to 1205 MPa. The microhardness is greatly improved as compared with as-deposited IN718, and the highest microhardness reaches 485 HV. The results provide a technical support and reference for formulating the heat treatment schedule of IN718 prepared by SLM.