CeO_(2)对TiC_(x)增强钛基激光熔覆层成形质量和组织的影响

Effects of CeO_(2) on Forming Quality and Microstructure of TiC_(x)-reinforced Ti-based Laser Cladding Coating

采用同轴送粉激光熔覆技术在Ti6Al4V钛合金表面成功制备了未添加和添加质量分数为2%CeO2的Ti6Al4V+NiCr-Cr3C2多道搭接熔覆层,运用渗透探伤技术、光学显微镜、X射线衍射仪、扫描电镜、能谱分析仪、电子探针等分析方法研究了CeO2添加对熔覆层成形质量、微观组织和元素分布的影响规律。结果表明,添加CeO2完全抑制了熔覆层表面裂纹,显著降低了气孔率(2.76%→1.65%)。熔覆层主要由β固溶体(CrTi4)和缺位型碳化钛(TiCx)组成。除了新结晶的CeO2外,添加CeO2对熔覆层物相没有影响。此外,添加CeO2致使基体β相中Ni和Cr元素呈现明显的偏析现象,且Ni元素偏析程度更加显著,而对Al和V元素均匀分布特征没有显著影响。新析出的稀土氧化物CeO2主要分布于TiCx与CrTi4相界处。添加CeO2细化了TiCx枝晶,降低了枝晶TiCx含量(55%→40%)。熔覆层各微区(熔覆区、过渡区和结合区)碳化钛组织存在显著差异,其组织特征分别为枝晶状、颗粒状、细小针状。缺位型碳化钛TiCx中C原子含量呈现明显差异,x的取值范围为0.21~0.74,且一次枝晶含碳量高于二次枝晶。硬度和摩擦磨损测试结果表明,Ti6Al4V基材、未添加和添加质量分数为2%CeO2激光熔覆层的显微硬度分别为363.2、488.2和464.2 HV0.5,磨损率分别为5.62×10-6、2.5×10-7和2.43×10-6g/Nmin。

Ti6Al4V+NiCr-Cr3C2 multi-track overlapping cladding coating without and with 2%CeO2 was successfully prepared on the surface of Ti6Al4V via using coaxial powder feeding laser cladding technology.The effects of CeO2 addition on the forming quality,microstructure and element distribution of cladding coating was investigated by penetrant flaw detection technology,OM,XRD,SEM,EDS,EPMA and other analytical methods.The results show that the addition of CeO2 completely inhibits the surface cracks on the cladding coating and significantly decreases the porosity from 2.76%to 1.65%.The microstructure of cladding coatings are mainly composed ofβsolid solution(CrTi4)and vacant titanium carbide(TiCx).The addition of CeO2 has no effects on the phase types of the cladding coating except for the recrystallized CeO2.Futhermore,the addition of CeO2 leads to a distinct segregation of Ni and Cr element in the matrix,especially for Ni,while elements Al and V are relatively evenly distributed.The recrystallized CeO2 is mainly distributed at the phase boundary between the TiCx and CrTi4.Adding CeO2 refines the TiCx dendrite and reduces the relative content of dendritic TiCx from 55%to 40%.The microstructures of titanium carbide in the different zones(such as cladding zone,transitional zone and bonding zone)of the cladding coating are exhibited significant difference,and their microstructural features are dendritic,particulate,and fine needle-like,respectively.The content of element C in the vacant titanium carbide TiCx also shows a significant difference,the value of x ranges from 0.21 to 0.74,and the C in primary dendrite is higher than that of secondary dendrite.The results of hardness and friction wear test show that the microhardness of Ti6Al4V substrate,the composite coatings without and with 2%CeO2 is 363.2,488.2 and 464.2 HV0.5,respectively.And the wear rates are 5.62×10-6,2.5×10-7 and 2.43×10-6 g/Nmin,respectively.