Research On High Wear-Resistance Performance And Wear Mechanisms For Hardfacing Coatings Of WC Reinforced Cu-Ni-Mn Metal Matrix

As one of the most serious failure modes in engineering applications, wear leads to the failure of components and causes enormous material and energy loss, which results in huge economic loss. Hardfacing process is an effective way to improve wear resistance by applying a wear resistant coating on the surface of easy to wear components, which not only can repair wear failure components,, but also extent the service life of components and reduce material and energy loss significantly. This paper designs a tungsten carbides reinforced Cu-Ni-Mn based metal matrix composite flux-cored wire and a kind of WC/Cu-Ni-Mn composite coating is deposited on a 20 steel substrate by a hardfacing method. The hardfacing coating is age-hardening treated, its microstructure, mechanical properties and wear resistance under three-body abrasive wear and frictional wear condition are investigated, and the wear failure mechanisms under the different test conditions are also investigated.The microstructure and the mechanical properties of the WC/Cu-Ni-Mn hardfacing are investigated. The results show that the Cu-Ni-Mn metal matrices of the WC/Cu-Ni-Mn hardfacing coatings consists of the predominantly primary dendrite structure. The primary phase in the as-deposited Cu-Ni-Mn metal matrix contains a kind of FCC crystal structure solid solutions(α-Cu) and a new NiMn phase precipitates at the grain boundaries of theα-Cu dendrites after the age-hardening treatment. The hardness of the as-deposited and the age-hardening treated Cu-Ni-Mn metal matrices is 125 HV0.2 and 319 HV0.2 respectively.The tensile strength of the as-deposited and the age-hardening treated Cu-Ni-Mn metal matrices is 473 MPa and 832 MPa, otherwise, the elongation is 33% and less than 1%,respectively. There are no pores, cracks or other defects can be observed in the WC/Cu-Ni-Mn hardfacing coating. The WC particle reinforcement whose volume fraction is 63% is uniform distributed in the hardfacing coating and no concentration of reinforcements happened throughout the hardfacing coating. What’s more, the WCparticles in the hardfacing coating are not dissolved obviously during the weld process.The wear resistance of the WC/Cu-Ni-Mn hardfacing coating under the three-body abrasive wear condition is tested, and the corresponding wear failure mechanisms are investigated. It is found that the wear resistance of the WC/Cu-Ni-Mn hardfacing coating is approximately 4 times more resistant than high-Cr cast iron under 3-body abrasive wear condition when the abrasive is silica sands. The major wear failure mechanisms are the plastic deformation and ductile flow of the Cu-Ni-Mn matrix, and the fracturing of WC particles.The frictional wear resistance of the WC/Cu-Ni-Mn hardfacing coating under room temperature and 350 ℃ is investigated, and the corresponding wear failure mechanisms are also analyzed. The relative resistance values of the as-deposited and the age-hardening treated WC/Cu-Ni-Mn hardfacing coating to the high-Cr Fe-Cr-C hardfacing coating of British WA company under room temperature are 1.83 and 2.26, and the relative resistance values under high temperature are 1.90 and 2.39, respectively. The dominate sliding wear mechanisms of the hardfacing coating are severe abrasion wear and severe adhesion wear when tested at room temperature. Abrasion wear, adhesion wear as well as oxidation of the surface of the hardfacing coating are the main sliding wear mechanisms under high temperature. This kind of metalic oxidant plays a positive role in promoting the sliding wear resisitance properties at high temperature in this paper.The frictional wear behaviours of the WC/Cu-Ni-Mn hardfacing coating under room temperature and high temperature are comparative analyzed. The results show that the wear process of the hardfacing coating is characterized by two typical periods during the friction wear test: running-in period and steady period. The dynamic friction coefficient values of the hardfacing coating at high temperature are lower than that of the values when the specimens tested at room temperature, this result is owing to the formation of the transfer layers contains metalic oxide between the friction coating/counter disc couple which could act as lubricant to deduce the dynamic friction coefficient values during wear.Under high temperature, the wear volume loss of the hardfacing coating specimens is higher than that of the specimens tested under room temperature, which is the comprehensive result of the negative softening effect and the positive oxidation effect of the Cu-Ni-Mn metal matrix, with the former dominant.