Fe–W–C thermodynamics and in situ preparation of tungsten carbide-reinforced iron-based surface composites by solid-phase diffusion

Abstract

Tungsten carbide (WC)-reinforced Fe-based surface composites were prepared by in situ solid-phase diffusion at 1423K for 4, 6, and 8h. The thermodynamics, phase composition, microstructure, microhardness, and wear-resistance of the Fe–W–C ternary system of the samples were examined by X-ray diffraction, scanning electron microscopy, Vickers hardness test, and wear test, respectively. Thermodynamic calculations showed that the thermodynamically favored products of the Fe–W–C system were W2C, WC, and Fe3C. W also exhibited a stronger carbide-forming tendency than Fe. The Gibbs free-energies of W2C and WC, which were stable carbides, significantly decreased with increased temperature. The main phases of the composite were WC, γ-Fe, Fe3C, graphite, and η-carbide (M6C) with fishbone-like morphology. The longitudinal section of the composite could be easily divided into three reaction zones, namely, WC layer, “no graphite area,” and M6C-reinforced area. WC particles in the WC layer were irregularly shaped with 0.3–12μm particle size, with volume fraction of up to >80%. The average microhardness value of the dense ceramic layer was 2152HV0.1. The maximum relative wear-resistance, which was 230.4 times higher than that of gray cast iron, was obtained at 20N. The high wear-resistance of the composite was due to the in situ formation of dense and hard WC particulates that acted as a reinforcement phase.