Wear mechanism and nanoscratch properties of an NbC enhancement layer with a high volume fraction of submicron structures on an iron-based surface

In this paper, the high volume fraction of NbC (Niobium carbide) reinforced layer was prepared on the surface of iron by in situ reaction method using grey cast iron and high-purity Nb plate as raw materials. The phase-composition, morphology, microstructure, nano-mechanical properties, and deformation mechanism of the enhancement layer under continuous small loads were investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nanoscratching. The results show that the average grain size of NbC in the high volume fraction of submicron structured NbC enhancement layer is about 255 ± 38 nm. The NbC ceramic particles are closely connected with each other, and the crystal grain size is uniform. The NbC ceramic layer volume fraction is approximately 95%. During the nanoscratch experiment under continuous small loads, the compact NbC ceramic layer followed the order 'elastic deformation -> plastic deformation -> cracking', and only occurs as shallow ploughing wear and slight grain spalling under 650 mN. The toughening mechanism of the enhancement layer include high-strength bonding between ceramic particles, reinforcing and toughening of the high hardness and high modulus of NbC enhanced phase, and strengthening of fine grains.