Multi-material laser powder bed fusion (MM-LPBF) additive manufacturing of dual-phase heterostructure steel

Abstract

The multi-material laser powder bed fusion (MM-LPBF) additive manufacturing technology enables the refined fabrication of artificially designed and spatially ordered integrated structures of multiple metallic materials. Through the screening of dissimilar material matching based on compositional similarity and metallurgical compatibility, three types of the bimetallic integrated bulk materials with heterostructures of staggered multi-layer planes, staggered multi-layer chessboards, and staggered multi-layer rotating gratings, respectively, were fabricated via the MM-LPBF using 316 L austenitic stainless steel and 18Ni300 martensitic steel powders as the raw materials. The printed bimetallic configurations present the dual-phase and bimodal structure of fine-grained martensite phase, with body-centered cubic (BCC) crystal structure, and coarse-grained austenitic phase, with face-centered cubic (FCC) crystal structure. The dual-phase regions exhibit spatially ordered distributions according to the artificial designs. The interfaces between the dual-phase regions display firmly bonded through the "dual-phase interspersed and mixed" transition form after melting-solidification from the laser molten pool behaviors. The characteristic geometric dimensions of these spatially arranged phase regions from differentiated geometric types vary from 200 to 500 µm, with dual-phase mixing zones of 100 µm width as the interfacial regions. Considering the strength-ductility synergy effect of the bimetallic integrated material of the austenitic and martensitic steels, the dynamic impact performances of the heterostructures under different impact strain rate conditions were experimentally verified, showing good impact resistances and energy absorption capacities of these dual-phase, bimodal, and hierarchical heterostructures. This MM-LPBF additive manufacturing path is conducive to the creation of more novel alloy systems with strength-toughness synergy using more integrated dissimilar metallic materials.