Effect of carbon content on the microstructure and properties of NbC-Fe cermets

The aim of this work was to correlate the overall carbon content in NbC-Fe starting powders with the resulting microstructure, hardness and fracture toughness of Fe-bonded NbC cermets prepared by conventional liquid phase sintering for 1 h at 1400°C in vacuum. The microstructure, phase composition and thermal behavior were analysed by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry, and the Vickers hardness and Palmqvist fracture toughness were measured. The influence of the carbon content on the sinterability, carbide grain size, morphology, and cermet mechanical properties were elucidated. A lower carbon content resulted in the aggregation of NbC grains and an increased mass transfer rate, resulting in coarser NbC grains. With an increase in carbon content in the system, the carbothermal reduction of surface oxides occurred at lower temperatures, resulting in better sinterability, improved binder distribution and a refined microstructure with superior mechanical properties compared to lower carbon content cermets.