Study Of Thermal Fatigue Behavior Of Tungsten Carbide Particle Reinforced Steel Substrate Surface Composite

With the development of modern industry, there is more components and parts applied in many industrial fields, such as metallurgy, mechanical, electricity and so on,with high temperature wear and sharp quenching. The ceramics particle reinforced surface composite have advantages not only in ductility but also toughness, modulus, hardness and so on. This composite can meet the wear-resistance requirements. It is a great candidate for replacing traditional metal materials in some wear working condition. However, there is thermal fatigue of quench heat shock in some complex wear working condition, it means that the surface composite must have thermal fatigue resistance. The cast tungsten carbide particle reinforced steel substrate surface composite was processed by vacuum suction casting infiltration method. The connection between microstructure of surface composite and thermal physical characters, mechanism of thermal fatigue crack initiation and propagation etc. was studied by microstructure analysis, thermal fatigue behavior investigation, thermal physical characters test, thermodynamics calculation and mechanical calculation.The connection between microstructure and thermal physical characters(thermal expansion coefficient, thermal capacity, thermal diffusion coefficient and thermal conductivity) of the surface composite was studied. The results showed:(1)The constitutes of the surface composite are WC、W2C、Fe2W2C、Fe3W3C、Cr7C3and martensite basically.(2)From the macroscopic interface between composite and substrate to surface of composite, the volume fraction of particle is increasing gradually, meanwhile, it is inversely proportion to thermal expansion coefficient, thermal capacity, thermal diffusion coefficient and thermal conductivity.(3)The thermal expansion coefficient, thermal capacity, thermal diffusion coefficient and thermal conductivity is inversely proportion to particle size of surface composite.(4) Below630℃, the thermal deformation stability of surface composite is great, and it is inversely proportion to particle size.The oxidizability and thermal fatigue behavior were studied by experimental observation and thermodynamic calculation.The results showed:(1)The oxidation and crack depth of surface composite is below30μm after6thermal shock cycles.(2)The particle is oxidated to WO3, the oxidation reaction is W2C+3O2�'2WO3+CO2, the initial reaction temperature is570℃, the reaction rate is proportional to temperature.(3)Below570℃, the thermal fatigue behavior is influenced by thermal stress primarily, the thermal fatigue cracks are apt to initiate and propagate on the macroscopic interface.(4)Above570℃, the thermal fatigue behavior is influenced by oxidizability, the influence is enlarged with temperature increasement.The stress of macroscopic interface, microscopic interfaces and composite was calculated for studying the mechanism initiation and propagation thermal fatigue crack in deep. The results showed:(1)The thermal stress calculation model of surface composite is built.(2)the maximum stress of macroscopic interface is63.4MPa calculated by the model, it is much higher than the other areas of composite, the maximum stress of microscopic interface is38MPa.(3) The mechanism initiation and propagation of crack on macroscopic interface, the thermal fatigue cracks are apt to initiate and propagate on the macroscopic interface is testified by the calculation results.