| The mechanical properties of traditional titanium alloys cannot meet the requirements of high strength and toughness,and titanium matrix composites can combine matrix and reinforcement to play their advantages.The selection of reinforcement not only needs high strength and high hardness,but also needs good wettability with the titanium matrix to avoid the negative influence of reaction with the matrix.In this paper,the mechanical properties of titanium alloy were improved by adding silicon carbide phase with low density,high melting point,high elastic modulus,corrosion resistance and similar thermal expansion coefficient to TC4 alloy.In this work,silicon carbide nanowires(Si CNW)reinforced TC4 composites were prepared by mechanical stirring and and silicon carbide particles(Si Cp)reinforced TC4 composites were prepared by ball milling method.Vickers microhardness tester and universal electronic testing machine,XRD,SEM,OM was used to test and characterize.Hot rolling was used to further improve the mechanical properties of the composites and the microstructure and mechanical properties of the rolled composites were studied.According to the effect of sintering temperature on the microstructure,densities and mechanical properties of the material,the best sintering temperature of composite is 1000°C.The sintered Si CNW/TC4 composites showed a typical Widmanstatten structure and change to netbasket structure when the Si CNW content was 0.5 wt%.The addition of Si CNW refines the grain size of SiCNW/TC4 composite significantly and improves the hardness of the composite.According to the analysis of the tensile test results,the yield strength and ultimate tensile strength of the 0.5 Si CNW/TC4 composites were 893 Mpa and 961 Mpa,respectively,which were 13.2% and 6.7%higher than pure TC4 alloy,while the elongation was 4.0%.The reason for the descent of plasticity is that the agglomerated Si CNW weakens the binding force between matrix and reinforcements,resulting in microvoids and cracks around the Si CNW on the fracture surface.The main strengthening mechanisms can be attributed to the gain refinement and load transfer mechanism.The sintered Si Cp/TC4 composites of ?-Ti and ?-Ti phase.With the addition of Si Cp the grain size is refined and the vickers hardness of the composites is increased by 19% compared with TC4 alloy.The tensile test results at room temperature show that the addition of Si Cp can significantly enhance the strength of the composite.When the mass fraction of Si Cp was 0.5 wt%,the yield strength and ultimate tensile strength of the composite are 1053 MPa and1144 MPa,respectively,while the elongation decreases with the increase of the Si Cp content.The tensile fracture of sintered Si Cp/TC4 composites at room temperature shows a typical plastic fracture pattern.The SEM of the longitudinal results show that the cracks are mainly around the interface between Ti C and matrix.The main strengthening mechanisms of Si Cp/TC4 composites are grain refinement,load transfer and dislocation strengthening mechanisms.SiCNW/TC4 and SiCp/TC4 composites show the best properties after rolling at900? and 75% deformation.The yield strength and ultimate tensile strength of the rolled 0.5 Si CNW/TC4 composites were 1143 MPa and 1270 MPa,respectively,and the elongation was 4.1%.The yield strength and ultimate tensile strength of 0.5Si Cp/TC4 composites in the rolled state were 1113 MPa and 1233 MPa,respectively,and the elongation was 8.8%.Both sintered and rolled SiCp/TC4 composites exhibit relatively good mechanical properties due to the homogeneous dispersion of the reinforcement and the presence of Ti C.Different morphological silicon carbide is beneficial for improving the strength of TC4 composites,while high content of silicon carbide tends to lead to brittle fracture.Silicon and carbon alloying treatment will be a new way to improve strength and plasticity. |
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