Improved creep properties of Inconel 718 fabricated by selective laser melting from boron-phosphorus interaction

The inferior creep ductility of Inconel 718 (IN718) fabricated by selective laser melting (SLM), which is unable to meet aerospace material specification (≥4%), limits its engineering application. Despite persistent optimization efforts in the SLM process and post-heat treatment, this issue remains unresolved. This study involved SLM fabrication of the modified IN718 with trace amounts of LaB6 and/or P, followed by homogenization and double aging heat treatment. The addition of trace LaB6 notably influenced the recrystallized grain structure and carbide precipitation at grain boundaries, while trace P addition had minimal impact. All samples exhibited similar γ′ and γ″ strengthening precipitates. Creep tests conducted at 650°C/690 MPa revealed that the individual modification of LaB6 showed limited improvement in creep performance and P showed no improvement, but the combined addition of LaB6 and P led to a substantial enhancement in creep performance, especially reaching as high as 8.6% creep strain. This remarkable improvement in creep ductility is unlikely to arise from the altered grain structure and grain boundary precipitates induced by LaB6 but predominantly arises from the synergistic effect of P and B in enhancing resistance to crack propagation during the third stage of creep.