Impact Of Microstructure And Properties Of Nickel-based Alloy Surfacing Layer By Ultrasonic Impact Treatment

In this paper, based on the existing ultrasonic impact treatment (UIT) device of optimizing reconstruction, trying to the high quality, high efficiency, flexible, less pollution into the way of strengthening the main manufacturing nuclear-main-pump materials-Ni-based alloy surfacing layer surface hardening, trying to improve surface properties and microstructure of nickel-based alloy surfacing layer, make its surfacing layer the residual tensile stress change into the residual press stress, which can improve the fatigue strength of the surfacing layer. It’s to improve running the safety and reliability of the nuclear-main-pump and extend the service life of the nuclear-main-pump provide technical support.This paper mainly using three-dimensional profilometer, X-ray diffractometer, scanning electron microscopy (SEM), electron probe microanalysis (EMPA), microscopic vickers hardness tester, friction and wear tester and three electrodes dynamic potential scanners. And the changed situation that surfacing layer of before and after UIT macro and micro structure, surface performance testing, and macro morphology and surface roughness, microstructure, composition, microhardness, residual stress, friction and wear and corrosion resistance performance are analyzed.Macrostructure and microstructure show that:Roughness of surfacing layer surface unchanged before and after UIT, but some surface defects by mechanical processing were compacted by impact needle. Before and after UIT, surface of nickel-based alloy surfacing layer will not phase changed. The microstructure of surfacing layer was mainly for the austenite dendrites+interdendritic eutectic compound. Before UIT, austenite dendrite was complete, and carbide (boride) was continuous. After UIT, the microstructure refinement, the carbide was crushed obviously. After UIT, surface microstructure become even, density; welding crack and defects loose were eliminated; composition segregation reduced significantly.The surface performance test shows that:Nickel-based alloy surfacing layer surface hardness increased obviously by ultrasonic impact treatment, increase70HVN. Ultrasonic impact treatment could evident improved stress state of nickel-based alloy surfacing layer that residual tensile stress of surfacing layer surface relaxed and decreased, the decrease+500Mpa above, part of residual tensile stress has been completely changed into the residual press stress which benefited extend the fatigue life for surfacing layer. Wear resistance was improved obviously. Surfacing layer surface friction coefficient of Before UIT-Surfacc, After UIT-Surface and After UIT-Core unchanged, but the depth of grinding crack reduced about5μm, and the wear volume of grinding crack reduced about30%. Ultrasonic impact treatment has no contribution to the surface corrosion resistance of Ni-based alloy surfacing layer. Namely, surface treatment of Ni-based alloy surfacing layer by ultrasonic impact treatment will not decreased the corrosion resistant in nuclear environment (Boric acid aqueous solution) when other surface properties were improved.This study will provides experimental and theoretical support in the area of UIT, especially in the application of strengthening surfacing layer...