激光熔覆CoCrNiMnTi_(x)高熵合金涂层组织及耐磨性能研究

Microstructure and Wear Resistance of CoCrNiMnTi_(x) High-entropy Alloy Coating by Laser Cladding

目的针对高铁制动盘等高速强力磨损的关键件,设计激光熔覆CoCrNiMnTi_(x)高熵合金涂层,提高表面的硬度和耐磨性。方法采用激光熔覆技术在Q235钢表面制备CoCrNiMnTi_(x)高熵合金涂层,利用XRD和SEM对涂层微观组织进行表征,通过显微硬度计和纳米压痕仪测试涂层硬度,运用摩擦磨损试验机和三维形貌仪研究涂层的摩擦磨损性能。结果在激光熔覆CoCrNiMnTi_(x)涂层中,随着Ti含量的增加,涂层物相由单一的FCC相转变为FCC+Laves相。由于固溶强化以及Laves相含量增多,涂层的显微硬度不断提高,CoCrMnNiTi硬度达到523HV0.1,最高纳米硬度达到6.91 GPa。CoCrNiMnTi_(x)系涂层的弹性模量大小相近。随着Ti含量的增加,涂层的耐磨性呈现升高趋势,当Ti的摩尔分数增加至0.75时,涂层具有最好的耐磨性,但进一步增加Ti含量时,由于脆硬性的Laves相逐渐增多,磨损形式由低Ti含量时的粘着磨损逐渐转变为高Ti含量时的磨粒磨损,使涂层耐磨性能下降。结论激光熔覆CoCrMnNiTi_(x)涂层可以显著提高基体的耐磨性,Ti的摩尔分数为0.75时,在FCC基体中形成了少量Laves相,既提高硬度,又实现强韧配合,涂层表现出最佳的耐磨损性能。

For the key parts of high-speed and strong wear such as high-speed rail brake discs,CoCrNiMnTi_(x) high-entropy alloy coating by laser cladding was designed to improve the hardness and wear resistance of the surface.The CoCrNiMnTi_(x)(x=0,0.25,0.5,0.75,1)high-entropy alloy coating was prepared on the surface of Q235 steel by laser cladding technology,and the microstructure of the coating was characterized by XRD and SEM.The hardness of the coating was tested by a microhardness tester and a nanoindenter.The friction-abrasion testing machine and the three-dimensional profiler were used to study the friction-abrasion performance of the coating.The CoCrNiMnTi_(x) coating prepared by laser cladding technology had good coating quality and no defects such as pores or cracks.It is found that in the CoCrNiMnTi_(x) coating by laser cladding,with the increase of Ti content,the coating phase changes from a single FCC phase to FCC+Laves phase,and the diffraction peak of FCC solid solution gradually shifted to the left.The microstructure of the CoCrNiMn coating is columnar crystals.When the Ti content is 0.25,it transforms into equiaxed crystals;when the Ti content is higher than 0.5,Laves phase and eutectic structure appear in the intergranular region.Under the dilution effect of the laser cladding,the Fe on the surface of the Q235 substrate diffuses into the coating,and the Fe elements enrich.The inside of the crystal grain is the FCC matrix phase,and the intergranular area is the(Co,Fe)_(2)Ti Laves phase.Due to the solid solution strengthening and the increase of the Laves phase content,the microhardness of the coating continues to increase.The hardness of CoCrMnNiTi reaches 523HV0.1,and the highest nanohardness reaches 6.91 GPa.CoCrNiMnTi_(x)-based coatings have similar elastic modulus.With the increase of Ti content,the wear resistance of the coating shows a rising trend.As the Ti content increases,the average friction coefficient of the coating decreases,and it is the lowest at Ti0.75.According to the analysis of wear volume and wear scar morphology,when the Ti content is 0.75,it has the lowest wear volume,and the width and depth of the wear scar are the lowest,showing the best wear resistance.However,when the Ti content further increases,due to the brittle and hard Laves phase gradually increases.the wear form gradually changes from adhesive wear with low Ti content to abrasive wear with high Ti content,which reduces the wear resistance of the coating.CoCrMnNiTix coating by laser cladding can significantly improve the wear resistance of the substrate.When the Ti content is added to 0.75,a small amount of Laves phase is formed in the FCC substrate,which not only improves the hardness,but also achieves a strong and tough fit.The coating shows the best wear resistance performance.Therefore,when the addition amount of Ti element is 0.75,the CoCrNiMnTi0.75 high-entropy alloy coating has the best performance,which can be used for surface strengthening and repair of high-speed rail brake discs,and improve the service life and reuse of high-speed rail brake discs.