Effect of Heat Treatment on Microstructure and Mechanical Properties of K418 Superalloy Prepared by Laser Powder Bed Fusion

For the purpose of optimizing the microstructures and the resultant mechanical properties of K418 superalloy fabricated by laser powder bed fusion (LPBF), various heat treatments including direct aging and solution/aging treatments at various temperatures and durations are undertaken. The effect of heat-treated temperature and duration on microstructure and mechanical properties is studied systematically. The results show that the γ′ and metal carbide (MC)-type carbide precipitates are formed during heat treatment and growth with increasing solution and aging temperature, which have a significant impact on the mechanical properties of LPBF-ed K418 superalloy. Compared to solution/aging heat treatment, direct aging heat treatment is more conducive to improving the mechanical properties of materials. The as-built K418 superalloy exhibits a maximum tensile strength of ≈1169 ± 28.3 MPa at aging temperature of 800 °C for 16 h, while its elongation is relatively low, ≈4.83 ± 0.78%. The strengthening mechanisms have been confirmed by microstructure analysis to be secondary phase and grain boundary strengthening mechanisms.