Effect Of Y₂O₃ Addition On Microstructure And Wear Resistance Of Ti-based Laser Cladding Layers

TC4 titanium alloy has been extensively used in the aerospace,marine oil,national defense and military and other important fields owing to its low density,high specific strength and good processability.However,the low hardness and poor wear resistance of TC4seriously restrict its application in friction occasions.Therefore,in this paper,multi-track overlapping Ti-based wear-resistant composite coatings were in-situ prepared on a TC4 alloy surface using TC4+Ni45+Co-WC+Y₂O₃ mixed powders by coaxial powder feeding laser cladding technology.The effects of Y₂O₃ addition on the macro and micro forming quality and microstructure of the cladding layers were systematically studied,and the refinement mechanism of Y2O3 on the coating microstructure was revealed.The precipitation mechanism and heterogeneous nucleation regularity of TiB₂-TiC dependent growth structure composite phase were clarified,and the effect of Y₂O₃ on the microhardness and wear resistance was analyzed.It provides the experimental and theoretical basis for the control of microstructure,forming quality and mechanical properties of Ti-based wear-resistant composite coatings on TC4.The main research work of this paper is as follows:?1?Effect of Y₂O₃ on the forming quality and microstructure of Ti-based wear-resistant the laser cladding layersThe phase composition of the coatings with different Y2O3 contents remained unchanged and was mainly composed of TiC,TiB2,WC,Ti2Ni,Y2O3 and matrix?-Ti.With the addition of Y2O3,the surface cracks of the coatings decreased gradually,the thickness and dilution rate increased gradually,the nucleation rate increased significantly,the coating microstructure was significantly refined,the morphology of TiC in the coatings changed from coarse dendrite to petal-like and granular,and the uniformity of the coating microstructure was effectively improved.?2?Study on the TiB₂-TiC dependent growth structure composite phaseAccording to the calculation of Bramfitt's two-dimensional lattice misfit theory,the misfit between the crystal plane of TiB2?0001?and TiC?111?was 0.873%,which demonstrated that TiB2 could act as a very effective heterogeneous nucleus to refine the primary TiC,and the two phases formed a coherent interface.The low misfit between TiB₂and TiC indicated that the TiB₂-TiC composite phase could effectively bind and adhere to the growth during the mixing cycle of the molten pool,and the TiB2-TiC composite phase exerted a restricting,binding and dragging effect on the convection and stirring processes of the molten pool,which could prevent TiB2-TiC composite phase being ripped out from the matrix under harsh wear environment.?3?Effect of Y₂O₃ on the microhardness and wear resistance of Ti-based wear-resistant laser cladding layersWith the increase of Y2O3 content,the microhardness of the coating decreased gradually,and the fluctuation stability of microhardness illustrated a tendency of increasing first and then decreasing.3wt%Y₂O₃ coating showed the best fluctuation stability,and the microhardness was about 470?480 HV_0.5.The wear depth,wear surface area,wear volume and wear rate of the coating were basically the same,showing a tendency of decreasing first and then increasing.The wear volume of 3wt%Y2O3(114×10^-3 mm³)coating was the smallest,the wear resistance was the best,and the wear mechanism was abrasive wear.