Synthesis of nanostructured Fe–TiB2 composites with excellent mechanical properties via laser powder bed fusion

The mechanical performance of Fe–TiB 2 composites produced via conventional methods is limited by inadequate microstructure refinement, thereby restricting their application in high modulus steels (HMSs). To overcome this, we proposed a novel strategy integrating high energy laser–assisted prealloying and rapid in situ TiB 2 precipitation to fabricate nanostructured Fe–5vol.%TiB 2 (equivalent to Fe–2.4 wt%TiB 2 ) composites via laser powder bed fusion (LPBF) from a predesigned Fe–Ti–TiB 2 powder mixture. The optimized process yields a bulk sample with a remarkably refined microstructure characterized by in situ nano TiB 2 nanoparticles (20–150 nm) uniformly dispersed within a nearly equiaxed, texture–free α –Fe matrix with grain sizes less than 500 nm—an order of magnitude smaller than the matrix grains typically achieved in other additively manufactured particle–reinforced metal matrix composites. This microstructural refinement results in superior mechanical properties, with a Vickers hardness of ∼482.5 HV, a yield strength of ∼1027 MPa, and a Young's modulus of ∼239.8 GPa. Notably, the yield strength is ∼190% higher than that of Fe–20 vol% TiB 2 composites produced via conventional methods, and the specific Young's modulus (∼32 GPa cm 3 /g) is ∼23% greater than that of established metallic structural materials (∼26 GPa cm 3 /g). The significant grain refinement is attributed to the synergy of the solutes and in situ–formed TiB 2 nucleant, providing sustained heterogeneous nucleation in the Fe–Ti–B melt during solidification. Additionally, uniform nano TiB 2 particle distribution is achieved by the interaction between the recoil pressure and Marangoni convection, which thoroughly stirs the molten pool and prevents particle agglomeration.