The Effect of Cooling Rate on the Solutionizing of IN718 Superalloy Produced via Selective Laser Melting (SLM) Method

In the present study, IN718 super alloy was produced by selective laser melting (SLM) method and was imposed under solution heat treatment at temperature of 1040°C for 2 hours. Three different environments, such as water, air and furnaces were used to cool the samples after complete solution. The results of microstructural studies conducted by optical microscopy (OM) and field emission scanning electron microscopy (FESEM) showed that intermetallic precipitates were formed during the process, disappear after solution. In order to complete the FESEM results, X-Ray diffraction (XRD) test showed that in at all cooling rates, the only remaining phases of matrix are the austenite (γ) and carbides, which their locations are between the grains according to the microscopic images. This issue indicates the proper selection of solution parameters and proper execution of solution process. The micro hardness test showed that doing solution treatment to reduce the volume fraction or completely remove the secondary phase leads to decreased hardness. By increasing cooling rate, the hardness of samples was reduced, so that the hardness of sample chilled in 30 % water was reduced compared to the sample before the heat treatment.