Microstructure And Mechanical Properties Of In Situ TiC Reinforced Titanium Matrix Composites Prepared By Spark Plasma Sintering Of Ti-nanodiamond System

For particle reinforced titanium matrix composites,the size and distribution of reinforcement particles have a great influence on the comprehensive properties of the composites.In this paper,the TiC particles reinforced titanium matrix composites were prepared by in-situ reaction using the spark plasma sintering technique.The nano-diamond powder is the carbon source,and the pure titanium is the matrix.TiC/Ti composites with different reinforcement content were obtained by changing the volume fraction of nano diamond.At the same time,TiC/Ti composites prepared by different preparation techniques were obtained by adjusting the milling process and sintering process.The phase,particle morphology and distribution,matrix structure and fracture behavior of TiC/Ti composites were analyzed by X ray diffraction(XRD),scanning electron microscopy(SEM)and electron back scattered diffraction(EBSD).The mechanical properties of TiC/Ti composites were tested by tensile and compression at room temperature.The strengthening mechanism of different size reinforcement was analyzed,and the influence of the subsequent rolling on the microstructure and properties of the materials was studied.(1)Using the same material as well as the sintering process and different ball milling process,the TiC/Ti composites with different reinforcement sizes were prepared.When the rotational speed of ball mill is small,nano diamond dispersed better and the size of TiC particles in the composites is small.With the increase of the speed of ball mill,the aggregation of nano diamond is intensified,the size of the reinforcement increases,the plastic property of the material decreases,and the strength of the composite is improved.When the mill speed remain constant,increasing the milling time exacerbate the agglomeration of nano diamond,and therefore reduce the milling time can effectively reduce the particle size of TiC in composite and improve the material plasticity.(2)Using the same mixing process and sintering process,the TiC/Ti composites with different reinforcement content were prepared by using powder with nano diamond volume fraction of 0.2%,0.4%,0.6%,1.2%,1.8%,and2.4%,respectively.The volume fraction of nano diamond powder has great influence on the shape and appearance of the material.When the volume fraction of the nano diamond is less than 0.6%,the size of the reinforcement particles in the TiC/Ti composites is small and the dispersion is distributed.When the volume fraction of nano diamond is greater than 0.6%,the size of the reinforcement in TiC/Ti composites becomes larger.When the volume fraction of nano diamond is increased from 0.2% to 0.6%,the tensile strength of the material increases.The tensile strength of the composites reached 673 MPa when the volume of the nano diamond is 0.6%vol.Continue to increase the content of nano diamond,the tensile strength of titanium matrix composite is basically unchanged.When the content of nano diamond is less than 0.6%vol,the elongation of the material is relatively stable,and it is maintained at about 25%.Continue to increase the content of nano diamond,the elongation of the material decreased sharply.(3)In the case of low sintering temperature,the density of TiC/Ti composites is small,and there are a lot of pores in the material.Porosity allows the material to be of poor ductility and high strength.Raising the sintering temperature,the density of the material is increased,the strength of the material is decreased,and the plastic is greatly improved.Continue to raise the sintering temperature,the density of the material slightly improved,its plasticity and strength are also slightly enhanced.In the rolling process,the particle breakage of large size particles is broken,and the dispersion of the particles is dispersed with the flow of the matrix during the rolling process.In the rolling process,a large number of fine grains appear,and the grains are refined.At the same time,the [0001] axis of the grain is rotated to the vertical direction of the sample plane.In the process of rolling,the rearrangement of the dislocations generates a large number of sub grain boundaries.After rolling,the tensile strength and elongation of TiC/Ti composites are improved.