Study On The Preparation, Microstructure And Mechanical Properties Of5Vol.%TiC/Ti-6Al-4V Composites

TiC/Ti-6Al-4V (reinforced with5vol.%TiC) composites were prepared by insitu cast route in this study, and the subsequent heat treatment and sheet rollingwere conducted on the composites. Phase constitute, matrix microstructure and themorphology of TiC of the composites with different processing states wereinvestigated. The room and high temperature tensile properties of the differentlyprocessed composites were systematically tested and the strengthening andfracture mechanisms of the composites were investigated. At the same time, theoxidation resistance and oxidation mechanism of the as cast and as rolledcomposites were studied respectively.The XRD results showed that as-cast, heat treated and as rolled compositeswere all composed of α-Ti phase、β-Ti phase and TiC phase. In as-cast composites,the matrix microstructure exhibited typical α+β dual-phase microstructure and theeutectic TiC was equiaxial or long strip. Heat treatment was conducted on the ascast composites and the results indicated that the higher the heat treatedtemperature, the more obvious the granulation effect under the same holding time.The best comprehensive room and high temperature mechanical properties wereobtained when the as cast composites were heat treated at1075oC/10h followed by aircooling.The as cast composites were directly multi-step rolled. After rolling, TiCparticles were obviously fragmented and tended to align along the rolling direction.The as rolled microstructure was significantly refined compared to that of as castcomposites. Primary α phase and β transformed microstructure was observed inthe matrix microstructure. The tensile test results indicated that there existed nomuch difference in the as rolled tensile strength of the rolling and transverse direction, while the elongations in the rolling direction were much higher.The RT tensile strength, yield strength and elongation of the as rolledcomposites with a total reduction of90%were1292MPa,1191MPa and6.7%respectively. The increments were about37%,34%,605%respectively comparedto those of as cast composites, while the increments were about32%,34%,1017%respectively compared to those of1075oC/10h AC heat treated composites. At600oC, the tensile strength, yield strength and the elongation were644MPa,552MPa, and15.3%, respectively. The increments were about67%,67%,1.2%respectively compared to those of as rolled matrix alloy. The room and hightemperature fracture mechanism of composites were quasi-cleavage fractureincluding matrix ductile fracture and TiC cleavage fracture.The cyclic oxidation experiments at high temperature revealed that, hightemperature oxidation of composites basically followed Parabola principle at550oC. As temperature rose to650oC, the oxidation resistance of both the as-castand rolled composites obviously decreased. Oxidation of composites was initiatedat the TiC particles since interface between TiC and matrix alloy served aschannels of O atoms diffusion. The results also revealed that the oxidationresistance of the composite was improved after rolling.