Microstructures and properties of wire and arc additively manufactured steel matrix composites with addition of WC by gravity-driven side powder feeding

Abstract

Wire and Arc Additive Manufacturing (WAAM), which exhibits high deposition rate and low production cost, is a promising method for fabricating large-sized composite components. In this work, the WAAM process is applied to fabricate steel matrix composite components by introducing WC/Fe powder into the molten pool through gravity-driven side powder feeding. The effects of WC powder fraction on the microstructure, mechanical properties and wear resistance of deposited components have been investigated. The results reveal that WC particles are completely dissolved into the matrix for the specimen with 20 wt% WC powder, resulting in a fine bainite microstructure with W element. For specimens with WC powder fraction above 20 wt%, different structures of (Fe,W)6C phase, including discontinue and continue networks, fishbone type, and flocculent particles, are formed due to intensive reaction between WC particles and the matrix. The latter two structures are more likely to appear in specimens with high WC powder fraction. The specimen with low WC powder fraction exhibits quasi-cleavage fracture during the tensile test, while brittle fracture is observed for the specimen with high WC powder fraction. Tests prove that the mechanical properties and wear resistance have been improved by the addition of WC. The maximum strength, the maximum microhardness and the minimum wear loss are obtained for the specimens with WC powder fractions of 40 wt%, 100 wt%, and 80 wt% respectively. The improved properties of deposited composite components can be attributed to the synergistic effects of solution strengthening, precipitation strengthening of (Fe,W)6C phase, second strengthening of retained WC blocks and fine-grain strengthening.