In-situ Preparation And Microstructure Evolution Mechanism Of Tungsten Carbide Reinforced Iron Matrix Composites

Tungsten carbide reinforced steel or iron matrix composites(WC/Fe)are desirable wear-resistance materials,which have broad application prospects in many fields such as machinery,metallurgy and mining,etc.WC particles exhibit high hardness,good thermal stability and excellent interface compatibility with Fe.However,both ex-situ and in-situ synthesized,WC reinforcements are prone to dissolve into a molten pool at high temperature.Thus,the strengthening effect of WC in steel or iron matrix is restricted.In this work,WC/Fe were prepared by powder metallurgy-hot pressing sintering.The in-situ reaction process,microstructural evolution,thermodynamics,dynamics of WC reinforced iron matrix composites under the two temperature systems of solid-state diffusion and near-eutectic were investigated.The experimental results showed that:(1)Calculated formation enthalpies and cohesive energies for h-WC,?-W2C,Fe2W,Fe7W6,and Fe3W3C,their thermodynamic stability have the following sequence:h-WC>?-W2C>Fe3W3C>Fe7W6>Fe2W.Thermodynamic calculation of the phase equilibria in Fe-W-C system indicated that carbon content affects the temperature of the liquid phase appears,the amount of liquid phase and elements dissolved in liquid.(2)During ball-milling process of graphite and ferrotungsten,the particle size began to decrease sharply,and then agglomeration occurred.After longer milling time,the agglomeration slowed down,in which case the formation of amorphous also reduce free energy.(3)The main composite phases included WC and oc-Fe,the W2C and Fe3W3C phases emerged as intermediate phases.WC or Fe3W3C prepared by solid-state diffusion and near-eutectic are different in morphology.The existence of a local liquid phase is the main factor affecting the morphology of WC and Fe3W3C.Its effect on the reaction zone changed carbon content,which further affects the amount of liquid phase.Driven by the capillary driving force,the liquid dissolves WC,and this process increases the local carbon content(4)The faceted shape of the large grain surrounding leads to assume that growth proceeds by“recrystallisation”through the dissolution of the small contiguous crystals.Volume fraction changes of WC alter the growth mode.The sequence of coarsening process of in-situ WC is outside-in.In addition,the coarsening of WC spheres with each other lead to the three-dimensional continuity of spheres.