Laser additive manufactured high-performance Fe-based composites with unique strengthening structure

Abstract

Steel matrix composites (SMCs), reinforced by ceramic particles, have received a consistent attention in recent years. Using conventional methods to prepare SMCs is generally challenging, and the mechanical properties of conventionally fabricated SMCs are limited. In this study, we successfully fabricated high-performance SMCs by laser powder bed fusion (LPBF) of a composite powder consisting of Fe-based alloy powder and submicron-sized WC particles. The effect of laser energy density on the phase formation, microstructural evolution, overall density and resulting mechanical properties of LPBF-fabricated composites was investigated. The present results show that a novel Fe2W4C carbidic network precipitates in the solidified microstructure entailing segregations along the boundaries of cellular sub-grains. The presence of this carbidic network hampers the growth of sub-grains even at elevated temperatures, and hence, stabilizes the grain size though prepared at a broad range of different energy densities. The exact distribution of the Fe2W4C carbides depends on the employed laser energy densities, as for instance they are more uniformly distributed at higher energy input. The density of LPBF samples reaches the maximum value of 99.4 % at 150 J/mm3. In this parameter set, high microhardness of ∼753 HV, compression strength of ∼3350 MPa and fracture strain of ∼24.4 % are obtained. The enhanced mechanical properties are ascribed to less metallurgical defects, higher volume fraction of the martensitic phase and increasing pile-up dislocations resulting from the pinning effect by Fe2W4C carbide.