| With the development of the mould, the life of the mould becomes more and more important. The head reason about the failure of the mould is that the performance of material surface gets worse. So it is necessary to find an advanced surface modification technology to improve the life of the mould and retrench the cost or increase the productivity. TD is an advanced surface modification technology.The composition of salt bath and the course of processing have been studied in the present thesis. The structural transformation and morpha of the TD coating have been investigated by several methods, i.e. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and image analyzer (Image-Pro). The thermodynamics and kinetics for the formation of vanadium carbide are studied theoretically.The composition of salt bath and the course of processing have been studied. The results show that the appropriate composition of salt bath is 81 to 83 percent of borax, 14 to 16 percent of ferrovanadium and 3 percent of ferrosilicon. The optimal treating time is 4 hour. If Crl2MoV and T10 processed, the optimal bath temperature is 1000℃ and 950℃ respectively. The studies also show the reducer content could affect the structure of phase and the treating time could affect the thickness of layer.The properties of vanadium carbide are studied in this paper. The results show the TD coating exhibits a thin extremely hard (3200HV), exceptional wear resistance, anti- erosive and anti-oxidized (under 400℃) surface coating of vanadium.The thermodynamics and kinetics for the formation of vanadium carbide are studied. The results show the free energy change of the formation of vanadium carbide is always minus in the given condition according to the caculation. At the same time, a micro-mechanism and a macro-kinetics model for the formation of vanadium carbide have been established. The formation of vanadium carbide mainly depends on the diffusion and chemical reaction of the V atoms in salt bath and the carbon atoms in the substrate. |
