Preparation And Performance Of Modified Surface Layer Of Fe-based Alloy

With the continuous development of science and consumption of energy, new energy has became the focus of national competition. In currently,nuclear power is the most widely used new energy, due to the nuclear pump equipment worked at extremely harsh conditions, surface abrasion and corrosion are serious, which not only caused huge economic losses, but also threaten personal staff of security, so it becomes particularly important to use surface modification technology to extend the life of nuclear pump and make nuclear pump material localization. Surface modification technology has been deep into all aspects of the national economy, which can effectively reduce the waste of resources and develop circular economy. It could provide strong support for the sustainable economic development. Plasma welding technology as an important branch of surface modification technology, not only can change the microstructure of the material surface to improve the surface wear resistance and corrosion resistance, but also has advantages of small dilution rate, good formability and energy efficiency. Compared with the cobalt-based alloy and nickel-based alloy modified layers, iron-based alloy surface modified layers not only avoid harm radioisotopes, and have low prices. Adding rare earth elements will further improve the organizational structure of the surface-modified layer, which has very broad application prospects.In this subject, Fe-based alloy modified layer, Fe-RE-based alloy modified layer and Ni-based alloy modified layer were prepared on the nuclear pump material Z5CND16-05 martensitic stainless steel surface by plasma welding, process parameters were optimized, the performance of three layers were compared.The microstructure, chemical composition, constituent phases, microhardness, friction wear characteristics, electrochemical corrosion and cavitation performance of the modified layers were investigated by optical microscope, scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS), X-ray diffraction(XRD), microhardness tester, pin-dish abrasion tester, electrochemical corrosion and cavitation instrument.The experimental results showed: Fe-based and Ni-based alloy modified layer prepared by plasma welding metallurgically bonded well, after adding rare earth elements, the morphology of modified layer changed from crystal into fine equiaxed uniform, but rare earth new phase were not detected, Ni-based alloy modified layer showed directional growth at the interface. The average microhardness of Fe-based, Fe-RE-based and Ni-based alloy modified layers are 720 HV, 750 HV and 630 HV, the relative wear are 7.8, 13.5 and 7.3, respectively. In the wear process, chromium carbide dendrites played a supporting role on protecting the modified layers. The corrosion current density of Fe-based, Fe-RE-based and Ni-based alloy modified layers were 2.3×10-7Acm-2,1.7×10-7Acm-2,5.8×10-8Acm-2 in 3.5% NaCl solution at room temperature, cavitation weight loss after 4h were 52.5% 34.4% and 19.7 % of the substrate.