Achieving high strength and high ductility in WC-reinforced iron-based composites by laser additive manufacturing

Abstract

Strategies for fabricating iron-based materials with high strength and ductility are rare despite intense research efforts within the last decades. This main challenge, which must be overcome in synthesizing such materials, is described by the strength-ductility trade-off dilemma. This study provides a novel approach to achieve the synthesis of highly strong and ductile iron-based composites reinforced with a high weight fraction of WC particles (20 wt%) utilizing laser powder bed fusion (LPBF) as processing technique. Thereby, the LPBF-fabricated composite material has a multi-phase microstructure consisting of ductile austenite (main phase), highly strong martensite and carbidic precipitations extending across different length-scales. The precipitation of (Fe, W)3C type carbide at the Fe/WC interface is well controlled. Thus, a very thin reaction layer (< 500 nm) forms between the WC particles and iron-based matrix. Additionally, nano-scaled precipitations evolve along sub-grain boundaries and within the sub-grains and they show a high coherency with the iron-based matrix. These iron-based composites synthesized by LPBF show an excellent compressive strength of about 2833 MPa and large fracture strain of about 32 %. The following mechanisms contribute to the improved mechanical properties: (1) multiphase material system, (2) grain refinement, (3) substructures, (4) coherent multiscale interfaces and (5) nano-precipitations.