Experimental and Analytical Investigation on Stress Relaxation Behavior of IN718 Superalloy Made by Selective Laser Melting Method Subjected to Variable Initial Strains

In this paper, by performing heat treatment on IN718 superalloy specimens that are manufactured by additive manufacturing method, the purpose is to investigate the experimental and analytical behavior of stress relaxation. The 3D printed specimens were made by the selective laser melting (SLM) method and after homogenization and solution heat treatment; they were subjected to stress relaxation at the temperature of 650 °C with an initial strain of 1.1% and 2.1% for 8 hours. Due to investigate the effect of strain changes on the stress relaxation, the stress relaxation limit diagram, which is 119.55 and 514.35 MPa for strains of 1.1% and 2.1%, respectively, shows that the stress relaxation limit increases with the increase of the initial strain. Furthermore, by examining the stress relaxation behavior in the experimental specimens, it was found that the amount and slope of the relaxation curve is higher in the specimen with a strain of 2.1%. In the analytical study, the creep constitute equations were also used to investigate the stress relaxation behavior, which by checking the presented comparative curves, by recording the error amount of 2.17% and 3.85% for the strains of 1.1% and 2.1%, respectively, the result of the comparison indicates a good agreement between the analytical results and the experimental curves.