Fabrication, microstructure and abrasive wear characteristics of an in situ tantalum carbide ceramic gradient composite

A tantalum carbide (TaC) ceramic gradient composite was produced on the surface of an iron matrix by an in situ technique comprising a casting process and a subsequent heat treatment. In this study, the phase constituents, microstructure, microhardness, and wear resistance of the gradient composite were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), a Vickers hardness tester, and a wear resistance tester, respectively. The results showed that the gradient composite can be divided into three zones according to the variation in the volume fraction of TaC ceramic particulates, which can be labelled as follows: micro-nanostructure TaC ceramic dense layer, micro-structure TaC ceramic layer and TaC ceramic particulate composite layer, where the combination between the gradient composite and matrix present a perfect metallurgical bond. The mean micro-hardness of the TaC ceramic gradient composite gradually decreased from the upper surface to the matrix due to the TaC ceramic particulates growing larger and their volume fraction gradually decreasing in different reaction zones.The microhardness of the micro-nanostructure TaC ceramic dense layer was the highest (2028 HV0.1), and the average size of the TaC particulates in this layer was less than 200 nm, with a volume fraction of more than 95%. In addition, the relative wear resistance gradually increased from the matrix to the surface. The wear mechanism of zone [A] was mainly characterised by plastic deformation and a few microcracks, while zones [B] and [C] experienced a combination of micro-ploughing with some TaC particulates broken. zone [C] was also characterised by squeeze traces because of the increased matrix. On the whole, the surface TaC ceramic gradient composite effectively protected the iron matrix from serious abrasion.