激光熔化沉积CoCrNiNbW高熵合金耐磨及腐蚀性研究

Research on Wear Resistance and Electrochemical Corrosion Properties of CoCrNiNbW High Entropy Alloy by Laser Melting Deposited

目的解决Q235钢材料在实际应用中由于磨损、腐蚀导致使用寿命缩短问题,提升Q235钢表面的硬度、耐磨性和耐蚀性。方法利用激光熔化沉积技术在Q235钢表面制备无裂纹CoCrNiNbW高熵合金涂层。采用扫描电子显微镜、X射线光谱仪、光学显微镜表征其微观组织结构、元素分布和物相成分;采用显微硬度计、试块-试环摩擦磨损试验机分别测试高熵合金涂层和Q235钢的显微硬度和耐磨性能,研究涂层的强化机制和磨损机理;采用电化学工作站测试分析高熵合金涂层和Q235钢的电化学腐蚀行为,研究涂层的耐蚀性和腐蚀机制。结果CoCrNiNbW高熵合金涂层的微观组织主要由等轴晶组成,涂层中部和底部存在未熔化Nb和W颗粒,起强化相作用;主要物相由富含Co、Ni的FCC相及富含Nb的BCC相组成;高熵合金涂层的平均显微硬度为800HV0.2,约为基材的4倍;涂层的磨损机制以磨粒磨损为主,磨损率为2.315×10^(–5) g·m^(–1),约为基材的1/5;在质量分数3.5%的NaCl溶液中,高熵合金涂层具有更好的耐腐蚀性,腐蚀电阻约为基材的8倍。结论高熵合金涂层的显微硬度、耐磨性和耐腐蚀性较Q235钢基材有很大提升。

The service life of Q235 steel is shortened due to wear and corrosion in practical application.It is necessary to improve the microhardness,wear resistance and corrosion resistance of Q235 steel surface.High entropy alloy(HEA)is a new type of high strength alloy with relatively uniform microstructure distribution and ideal mechanical properties and stable structure.Due to the characteristics of high hardness,good high temperature performance,excellent corrosion resistance and oxidation resistance,HEA is widely used in machinery manufacturing,aerospace,green processing surface engineering and other important fields which have great development potential and broad application prospects.A crack-free CoCrNiNbW high-entropy alloy coating was fabricated on the surface of Q235 steel by laser melting deposition technology in this artical.The substrate is Q235 steel.The surface is cleaned by laser cleaning machine(Shandong Haifu photon HFB-C50)to remove impurities on the substrate surface and prevent metal oxides and impurities from affecting the experimental effect.Apply the Laserline-4000 laser in the CoCrNiNbW cladding experiment.The optimum process parameters were determined after optimization.The moving speed of the spot is 8 mm/s during the cladding process;the laser power of the multi-pass cladding is 720 W,and the overlap between the two adjacent passes is 50%.The phase was analyzed by X-ray diffractometer(XRD)(Japanese science D/max-2500)(Cu target,acceleration voltage 40 kV,working current 140 mA).Optical microscope(Leica dvm6a),scanning electron microscope(Zeiss sigma 300)and X-ray spectrometer were used(EDS),accelerating voltage 15 kV.The macro morphology,microstructure morphology,composition and distribution of elements of the samples were observed.The dry sliding friction test of the coating was carried out by M-2000 friction and wear tester at room temperature.The material of the grinding ring is GCr15,the load is set to 120 N,and the wear time is 1 hour.After the wear experiment,collect the wear debris,observe the morphology of wear marks and wear debris,and analyze the wear type and wear resistance of the material.The electrochemical workstation(CHI-640)test was used to analyze the electrochemical corrosion behavior of the high-entropy alloy coating and Q235 steel.The electrochemical impedance spectroscopy,self corrosion potential and corrosion current density were analyzed by software,the electrochemical evaluation parameters of the samples were obtained,and the corresponding equivalent circuit was established.The microstructure of the CoCrNiNbW high-entropy alloy coating is mainly composed of equiaxed crystals,and there are unmelted Nb and W particles in the middle and bottom of the coating,which play the role of strengthening phase;The main phases are composed of the FCC phase rich in Co,Ni and the BCC phase rich in Nb.The average microhardness of the high-entropy alloy coating is 800HV0.2,which is about four times that of the substrate material.The wear mechanism is mainly abrasive wear,and the wear rate is 2.315×10^(–5) g·m^(–1),which is about 1/5 of the substrate material.In 3.5 wt.%NaCl solution,high-entropy alloy coating has better corrosion resistance,and the corrosion resistance is about 8 times that of the substrate.The microhardness,wear resistance,and corrosion resistance of the high-entropy alloy coating are greatly improved compared to the Q235 steel substrate.