Microstructure Control And Wear Resistance Of (TiC+TiB) Reinforced Titanium Matrix Composites Synthesized Using In-situ Technology

Titanium matrix composites（TMCs）have high specific strength,large specific stiffness,and excellent high-temperature resistance,which have been widely attention and developed rapidly in recent years.In-situ particles reinforced titanium matrix composites have been widely used due to their superior properties such as isotropic,easy to forming,low cost,and so on.With the development of titanium matrix composites,the study of the wear resistance for the titanium matrix composites becomes more and more important based on the practical application of all kinds of needs.In this paper,TiC and TiB reinforced titanium matrix composites are synthesized using in-situ technology of casting,and the matrix is Ti-5.5Al-4Sn-4Zr-0.3Mo-1Nb-0.5Si-0.06C（IMI834）.The volume fraction of reinforced phases is 0%,2%,4%,6%,8%and 10%,respectively.The volume ratio of TiC and TiB is 1:1.The reinforced phase volume fraction of 6%composites were treated by different heat treatment and alloying of rare earth La in order to optimize the microstructures and improve mechanical properties of the alloy.The results showed that:（1）For the different volume fraction of titanium matrix composites prepared by casting,reinforced phases uniformly distribute in the matrix.With the increase of the volume fraction of TiC,they grow up from near equiaxed shape to long strip,and finally dendritic shape.TiB phases show acicular shapes and short fibrous shapes,and the matrix shows lamellar structure.The grain size of matrix nearby reinforced phases is decreased.The wear resistance is significantly improved compared with the titanium alloy matrix.When the volume fraction of the reinforced phase is 10%,the wear resistance is the best.The wear volume is 6.879mm³,which is reduced by 49%compared with matrix,and the Rockwell hardness is 55HRC.The required time for friction and wear to reach the stable stage enhances with the increase of the reinforced phase,while the friction coefficient is decreased,and the lowest is 0.25 at 10%.The wear mechanism is combined effects of adhesive wear,abrasive wear and oxidation wear.After adding the enhanced phase,the adhesion and oxidation wear are weakened,and the abrasive wear is enhanced.（2）After heat treatment,microstructures of matrix occur different degree of primaryαcoarsening,which transform from lamellar structure into a duplex structure.Strip TiC phases occur fusing,granulation and dissolution,resulting in the decreased of volume fraction of enhanced phases.But there are no significant change for TiB phases.The optimal mechanical property is obtained by solid solution under 1050℃and 6h insulation.The compressive strength increases from 1607MPa to 1949MPa,and the compression ratio is 23%,and Rockwell hardness is 58HRC,and the friction coefficient is0.25,and the wear volume is 3.638mm³.The optimal mechanical property of alloy after aging at 500℃/8h is got,and compressive strength reaches 1940MPa,and the compression ratio is22%,and Rockwell hardness 55HRC,and the friction coefficient is 0.26,and wear volume is5.634mm³.（3）After adding La,the products of spheroidal La₂O₃ can refine the matrix and TiC particles.The TiC phases can not grow into long strip,and they have a tendency to distribute along the grain boundary.When the content of La is 0.2%,the mechanical property is the best.The Rockwell hardness is 55HRC,and the friction coefficient is 0.24,and the wear volume is 6.04mm³.