Effect of solution temperature on the microstructure and mechanical properties of Hastelloy X superalloy fabricated by laser directed energy deposition

In this study, the effect of solution temperature on the microstructure and mechanical properties of Hastelloy X fabricated by laser directed energy deposition (LDED) was investigated. As a result, the microstructure of as-deposited (AD) sample was mainly coarse columnar grains directionally growing along the deposition direction. Due to the segregation of Mo and Cr, a lot of Laves phase precipitates in the inter-dendritic. With the increase of solution temperature, the volume fraction of Laves phase gradually decreases. When the solution temperature increased to 1200 °C, the grains of the LDED Hastelloy X superalloy exhibited fully recrystallization, and then became coarse with the solution temperature of 1225 °C. With the dissolution of the Laves phase, the microhardness of the samples drops from 231 ± 5 HV to 211 ± 5 HV. The room temperature tensile results reveal that the as-deposited sample with irregular and long-striped Laves phase presents the worst tensile strength (652 ± 10 MPa) and elongation (30 ± 2%). After heat treatment, the strength and elongation of the LDED Hastelloy X superalloy gradually increased with increasing the solution temperature. When the solution temperature was 1200 °C, the tensile strength of the sample reached the maximum value of 720 ± 1 MPa. With the increase of solution temperature, the elongation increased and then reached the maximum value of 47 ± 2% with heat-treated at 1225 °C. The tensile fracture of LDED Hastelloy X superalloy with solution treatment presented a ductile fracture pattern.