WC-Ni-Co硬质合金表面激光熔凝修复组织与摩擦磨损性能

Microstructure and Friction-Wear Properties of WC-Ni-Co Cemented Carbide with Surface Laser Melting

目的为实现WC-Ni-Co硬质合金的表面疲劳裂纹缺陷修复,研究不同预热温度对合金表面激光熔凝层组织、显微硬度及摩擦磨损性能的影响规律。方法采用4 kW光纤激光器制备了不同预热温度的WC-Ni-Co硬质合金熔凝层,用着色探伤剂检测表面裂纹,用光学显微镜(OM)和扫描电镜(SEM)观察熔凝层的显微组织,用能谱仪(EDS)和X射线衍射仪(XRD)测定熔凝层的元素分布和相组成,用显微硬度计和磨损试验机测定熔凝层的硬度和耐磨性能,并观察了熔凝层的磨损形貌,分析熔凝层的磨损机理。结果熔凝层包含原始WC相、α-Co基体相、共晶鱼骨状碳化物、弥散分布的细小二次碳化物等组织,与基材WC颗粒的不规则形状相比,经熔凝后WC颗粒发生了明显的长大和界面平直化,且共晶鱼骨状碳化物为WC、Cr_(7)C_(3)、CoC_(x)和C_(6)(CoCrNi)_(23)的混合物。熔凝层的范围随着预热温度的升高逐渐增加,最大达866.7μm;当预热温度达到400℃以上时,熔凝后得到的熔凝层没有产生裂纹。熔凝层的平均显微硬度达到934HV_(0.5),远高于基材硬度762HV_(0.5)。预热温度的升高会降低熔凝层的摩擦因数,提高表面的耐磨性。结论当预热温度达到或超过400℃时,熔凝层中的WC颗粒分布较为均匀,无裂纹等缺陷,具有较高的硬度和耐磨性。

To repair the surface fatigue crack defects of WC-Ni-Co cemented carbide and characterize the influence of different preheating temperatures on the microstructure,microhardness and friction and wear properties of the laser melting layer,this paper prepares the WC-Ni-Co cemented carbide melting layer with different preheating temperatures by 4 kW fiber laser,detects the surface cracks with the coloring flaw detection agent,observes the microstructure of the laser melting layer with optical microscope(OM)and scanning electron microscope(SEM),measures the element distribution and phase composition of the laser melting layer by the energy dispersive spectroscopy(EDS)and X-ray diffractometer(XRD),and its hardness and wear resistance through the microhardness tester and wear tester,as well as analyzes the wear morphology and wear mechanism of the laser melting layer.The laser melting layer contains four structures:the original WC phase,theα-Co matrix phase,the eutectic fishbone carbides and the dispersed fine secondary carbides.Compared with the irregular shape of the substrate WC particles,after the surface melting,the WC particles grow up significantly,the interface is flattened,and the eutectic fishbone carbide is a mixture of WC,Cr_(7)C_(3),CoC_(x) and C_(6)(CoCrNi)_(23).The range of the laser melting layer gradually increases with the increase of the preheating temperature,which is up to 866.7μm.When the preheating temperature reaches above 400℃,there are no cracks on the laser melting layer obtained after melting.The average microhardness of the laser melting layer reaches 934HV_(0.5),which is much higher than the substrate hardness of 762HV_(0.5).With the increasing of preheating temperature,the friction coefficient of the laser melting layer will decline and the wear resistance of the surface will improve.When the preheating temperature reaches or exceeds 400℃,the laser melting layer is featured with uniform distribution of WC particles,no defects such as cracks,and higher hardness and wear resistance.