Ni对钛合金表面稀土激光熔覆层中TiC生长的影响

Influence of Ni on TiC growth in rare earth laser clad layer on titanium alloy

利用同步送粉激光熔覆技术,在Ti811钛合金表面激光熔覆原位合成了TiC和TiB_2颗粒增强镍基复合涂层。利用X射线衍射仪（XRD）、扫描电镜（SEM）、能谱分析仪（EDS）分析了熔覆层的显微组织和物相组成,利用显微硬度计测试了熔覆层的显微硬度。试验结果表明,激光熔覆涂层与基体呈冶金结合,涂层的物相主要由α-Ti、TiC、Ti_2Ni和TiB_2组成,其中TiC呈树枝晶状和花瓣状,TiB_2呈长条状。平衡状态下TiC以正八面体晶体结构存在,但熔体中存在的Ni元素会影响TiC平衡状态,使其最终呈现六边形形貌。稀土氧化物Y_2O_3的加入有利于促进晶粒细化,提高熔覆层组织均匀性及表面硬度。熔覆层的显微硬度显著提高,最高硬度为900HV0.5左右,约为基底硬度的2.25倍。

TiC and TiB_2 particles reinforced Ni-based composite coating were in-situ synthesized by using synchronous powder feeding laser cladding technology on Ti811 titanium alloy surface.The microstructure and phase composition of the laser clad layer were analyzed by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and energy dispersive spectroscopy（EDS）,the microhardness of clad layer was tested by microhardness tester.The results show that the laser clad coating is metallurgically bonded with the matrix,the main phases of the coating consist of α-Ti,TiC,Ti_2 Ni and TiB_2,in which Ti C is dendritic and petal shape,and TiB_2 shows long strip.In the equilibrium state,Ti C exist as a regular octahedral crystal structure,bute the Ni in the melt can affect the equilibrium state of Ti C and finally presents the shape of hexagon.The addition of rare earth oxide Y_2O_3 can promote grain refinement and improve the microstructure uniformity and surface hardness of the clad layer.The microhardness of the clad layer is significantly improved,and the maximum hardness is about 900 HV0.5,which is about 2.25 times higher than that of the substrate.