Microstructre And Wear Properties Of Ni-based Alloy Hardfacing Deposited By Plasma Transferred Arc Welding

The Ni-based alloy have many advantages, such as a lower melting point, good liquidity, abrasive resistance, corrosion resistance, oxidative resistance. Meanwhile, the cost is lower than that of Co-based alloy. In order to improve the abrasive resistance of stainless steel used in nuclear pump, the Ni-based alloy is deposited on the surface of stainless steel by plasma tranferred arc welding. It not only make the best of excellent performance of Ni-based alloy, but also save the precious metals.The coating of the Ni-based alloy was charaterized by metalloscope, electron probe, X-ray diffractometer, fluorescence spectrum analyzer, scanning electron microscope, and microhardness tester. The friction and wear properties were investigated on the MMS-2A friction-wear testing machine. The scanning electron microscope was used for wear surface morphology, which was intended for analysing the wear mechanism. Besides, the influence of welding current and different alloy powder for the microstrcture, microhardness, and wear resistance were researched.The results indicate that the microstructure morphology of the Ni-based alloy coating varied with the distance from the fusion line. The coating consisted of y-Ni matrix and the other precipitates, such as CrB, M23(C,B)6,Cr7C3, Cr5B3, and Ni3Si. The microhardness varied with the distance from the fusion line and the hardness of the middle layer was lower than the other area. The effect of wear technological parameter on friction and wear properties were investigated. With the increase of the load, the wear weight and the friction coefficient decreased. With the increase of the revolving speed, the friction coefficient decreased and the wear weight decreased firstly and increased subsequently. With the increase of the time, the wear weight increased, but the wear rate and the average frction coefficient reduced. When the roughness was reduced, the wear weight decreased firstly and increased subsequently. The wear mechanism included to adhesive wear, abrasive wear, oxidation wear, and fatigue.The influence of welding current on microstructure and properties was significantly. When the current was lower, the forming performance was poor. When the current was high, the coating ablator appeared and the properties dropped rapidly. The microstructure was mess under the current of140A and that was coarse under190A. When the welding current was160A, the coating had good forming performance, fine microstructure, the highest hardness, and the excellent wear resistance. The microstructure and properties of coating were influenced by the element content of Ni-based alloy powder. The microstructure of Ni40A alloy coating, which consisted of dendrite and intercrystalline precipitates, had the lowest hardness and the worst wear resistance. The dendrite was fewer and morphology was diverse of Ni50A alloy coating. A amount of borides and carbides distributed on y-Ni matrix of Ni60A alloy coating, which had the highest hardness and excellent wear resistance.