Tailoring microstructure and mechanical properties of IN738LC fabricated by laser powder bed fusion through processing parameter optimization

Abstract

IN738LC has been widely used in hot-end components owing to its excellent high-temperature performance, while it has still suffered from metallurgical defects during laser powder bed fusion (LPBF) due to its high crack sensitivity. This study investigated forming behavior, microstructure evolution and mechanical property of LPBF-processed IN738LC samples at different parameters (laser power of 150–300 W, scanning speed of 500–1500 mm/s). The result indicated that the decrease in energy density caused the width and depth of the melt pool to decrease and eventually broke into droplets, leading to an increase in porosity. As the scanning speed increases, the microstructure changes from irregular columnar/cellular dendrites to all distributed as columnar dendrites, exhibiting epitaxial growth. An optimal process window was finally obtained at a laser power of 200 W and a scanning speed of 1000 mm/s, which achieved excellent forming quality (the porosity of 0.01 %) and mechanical properties (microhardness of 445.5 HV, ultimate tensile strength of 1335 MPa and elongation of 19.3 %). This study provides process basis for subsequent studies of IN738LC fabricated by LPBF.