Grain refinement and strengthening of PH 13-8Mo martensitic stainless steel through TiC/TiB2 inoculation during wire arc additive manufacturing

Abstract

This research investigates the role of TiC/TiB2 nano-inoculants’ addition to the PH 13-8Mo martensitic stainless steel structure during wire arc additive manufacturing (WAAM). The microstructural analysis revealed that the introduction of the ceramic-based inoculants promoted the transition of columnar-to-equiaxed grain structure, refined the primary δ-ferrite grains, slightly increased the retained austenite content, and provoked the precipitation of in-situ TiC/M3B2 phases. Additionally, mechanical properties investigations showed that the TiC/TiB2 inoculation abated the anisotropic ductility as compared to the non-inoculated sample, and also improved the microhardness and tensile strength. Moreover, post-printing solutionizing and aging treatments were found to further enhance the hardness and strength of both TiC- and TiB2-reinforced components owing to the precipitation of nano-sized β-NiAl phases, while the accumulation of M3B2 phases in the intergranular regions led to the embrittlement of the TiB2-inoculated sample. This work, for the first time, illustrates the great potential for the adoption of ceramic-based nanoparticles as reinforcing/grain refining agents during the WAAM process for the fabrication of reinforced-PH 13-8Mo stainless steel components with a homogenous microstructure, nearly isotropic behavior, and superior mechanical performance.