Fabrication and microstructure of in situ vanadium carbide ceramic particulates-reinforced iron matrix composites

In this work, a novel process that combines infiltration casting with subsequent heat treatment was applied to fabricate in situ vanadium carbide (V8C7) ceramic particulates-reinforced iron matrix composites. Based on the differential scanning calorimetry (DSC) data, the as-cast samples were subjected to heat treatment at 1164 °C for different dwelling times (0, 10, 15, and 20 min). The effects of different heat treatment times on the phase evolution, microstructure, and microhardness of the as-prepared composites were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and Vickers hardness tester, respectively. The experimental results revealed that only graphite, α-Fe, and V8C7 phases dominate in the composite samples after heat treatment at 1164 °C for 20 min. The average microhardness of the as-prepared composites varied among the different regions as follows: 458 HV0.05 (vanadium wire), 1055 HV0.05 (composite area), and 235 HV0.05 (iron matrix). The microhardness of the composite region is four times higher than that of the iron matrix and two times higher than that of the vanadium wire because of the formation of the vanadium carbide phases (V2C and V8C7) as reinforcement within the iron matrix.

► A subsequent heat treatment promotes the formation of V8C7 particulates.
► Higher carbon-to-vanadium ratio is beneficial to form V8C7 particulates.
► Vanadium has a stronger carbide-forming tendency than iron.
► The diffusion reaction region broadens with increasing heat treatment time.
► The diffusion reaction region shows the highest microhardness value.