Effect of Preheating Temperature on Microstructural and Mechanical Properties of Inconel 718 Fabricated by Selective Laser Melting

Various studies related to additive manufacturing (AM) have been conducted with Ni-based superalloy and multiscale investigations of widely used Inconel 718 superalloy have been actively performed with the selective laser melting (SLM) method. The formation of defects and thermal residual stress during the SLM process could particularly affect product quality and life-time. Thus, to optimize the SLM process condition for Inconel 718 boasting the minimum of deteriorating properties, the microstructural study was conducted with various energy densities and preheating temperatures. The SLM process condition over 99.9% of density was established and the change of microstructural and mechanical characteristics were confirmed according to the preheating temperature from 50 to 150 °C. The fraction of the low angle grain boundary (LAGB) and the stored strain energy per unit volume gradually decreased as the preheating temperature increased. In particular, while maintaining the mechanical properties, the thermal residual stress in the direction perpendicular to the building direction decreased under the half value of yield strength which could induce deformation.