Microstructure And Mechanical Properties Of In-situ Fabricated Laminated Structure Titanium Matrix Composites

The incorporation of particulate reinforcements into titanium alloys can improve the specific strength and specific stiffness,while inevitably reduce the plasticity and ductility.In this study,in situ synthesized multilayer titanium matrix composites were designed by learning from the microstructure of nature biological materials with excellent mechanical properties.The effects and mechanism of laminated structure design for titanium matrix composites were studied by microstructure and mechanical properties analysis.Meanwhile,a simple and effective method was proposed by gradually optimizing process to fabricate laminated structure titanium matrix composites.Laminated structure titanium matrix composite consisting of alternatively arranged Ti layer and carburized Ti layer was fabricated by combined carburization and hot pressing connection method based on previous research results,which showed that both the surface hardness of Ti-6Al-4V alloy and its composite could be improved by one time than that of the untreated materials through solid carburization.However,the laminated structure composite shows unsatisfactory mechanical properties due to the high brittleness of the interface and carburized Ti layer,which results in rapid brittle fracture of the composite at the low elongation of only0.53%.Inspired by the strong designability of powder metallurgy,the laminated structure Ti-?TiB+La₂O₃?/Ti composite with relative density of 95%was prepared through vacuum sintering at 1573K,followed by hot processing to optimize the microstructure.The results show that pore defects of the as-sintered composite are disappeared and the?-Ti grains are refined obviously after hot rolling at 1323K.Meanwhile,the agglomerates and Ti-La-O particles are well dispersed and distributed uniformly along the rolling direction.The tensile testing results indicate that the laminated structure Ti-10vol.%?TiB+La₂O₃?/Ti composite performs excellent comprehensive properties,which shows an improvement of 30%in elongation with less than 4%decline in tensile strength compared with the 5vol.%?TiB+La₂O₃?/Ti composites.Laminated structure Ti-?TiB+TiC?/Ti composites with different volume fraction of reinforcements were prepared by optimized powder metallurgy and hot processing method.The result shows that the fully dense composites are fabricated by vacuum hot pressing sintering at 1473K.The?grains in pure Ti layer align along the forging direction after hot forging at 1223K.Meanwhile,The agglomerated reinforcement particles in the composite layer are well dispersed and distributed uniformly in the pure titanium matrix.The tensile strength of laminated structure Ti-?TiB+TiC?/Ti composites improves nearly one time than that of pure titanium.Significant improvement in elongation is achieved after stress relief annealing at 823K.The increase in reinforcements volume fraction leads to slight increase in strength and obvious decline in elongation.The annealed Ti-5vol.%?TiB+TiC?/Ti composites performs excellent comprehensive mechanical properties,which displays an improvement of 3.8 times in elongation with less than 4%decrease in tensile strength compared with that of Ti-15 vol.%?TiB+TiC?/Ti composites.The introduction of laminated structure into titanium matrix composites can result in excellent comprehensive mechanical properties,which can be attributed to the synergistic effect of Ti layer and composite layer.The strong composite layer can improve the uniform plastic deformation of Ti layer,while the ductile Ti layer can hinder the propagation of cracks from composite layer.The results provide experimental and theoretical basis for fabricating the novel high performance laminated structure titanium matrix composites.