The investigation on the fabrication and microstructure of a novel core-shell structure reinforced iron matrix composite

Abstract

To make the steel/iron composites with better comprehensive mechanical properties, a novel iron matrix composite reinforced with three-dimensional core-shell structure (CS) reinforcing particulates is designed and fabricated via powder hot-pressing sintering process. Studies have shown that the CS consists of isolated soft W core and dense hard shell, that is, showing the structural characteristics of “inner soft and outer hard”. When the carbon content of the raw material powder Fe–W–C ternary system is 0, 0.5, 1.0, 1.5 and 2.0 wt%, the CS of W@(Fe7W6 + Fe2W), W@Fe3W3C, W@(W2C + WC + Fe3W3C)Ⅰ, W@(W2C + WC + Fe3W3C)Ⅱ, and W@(W2C + WC + Fe3W3C)Ⅲ is formed in the matrix, respectively. The formation of CSs with different characteristics is mainly due to the diffusion of Fe atoms and/or C atoms into the W lattice to undergo a diffusion-type solid state phase transformation to form corresponding compounds and the formation kinetics of different phases determined by different carbon concentrations. Furthermore, the results of nanoindentation and Vickers indentation show that the hardness of the shell layer is much greater than that of the metal W core and matrix, but its plastic deformation rate is much smaller than that of the metal W core and matrix. The metal W core and the iron matrix can significantly inhibit the length of the crack propagation, thereby improving the toughness of the composite. And the hard shell layer with high volume fraction can significantly improve the strength of the composite. Therefore, the iron matrix composite reinforced with three-dimensional CS reinforcing particulates is expected to obtain good toughness and excellent strength, and this work may provide a new strategy for the structural design of steel/iron materials.