Constructing Near-Network Microstructure via Heat Treatment for Synergistic Enhancement of Strength and Toughness in (TiB + TiC + La2O3)/TC4 Composite

To further improve the mechanical properties and wear resistance of 3 vol.% TiB + 3 vol.% TiC + 0.4 vol.% La2O3/TC4 composites, the TMCs were prepared in-situ by melting cast method and then heat treated by different processes. The effects of different heat treatment processes on the microstructure evolution, mechanical properties and tribological properties of composites were comprehensively studied. The results indicated that heat treatment can effectively decrease the size of alpha-Ti and reinforced phase and increase the proportion of HAGBs. After different heat treatment, the grain orientation is more random and the distribution of reinforced phase is more uniform. The compressive strength and toughness are significantly improved, and the strength-toughness synergy is effectively realized (as-cast: 1890 MPa, 17.52%, HT2: 2010 MPa, 20.65%). Compared with as-cast TMCs, the average COF and specific wear rate of TMCs after different heat treatments are decreased to varying degrees. The average COF were 0.343, 0.262, 0.215, 0.236, respectively. The specific wear rates were 2.36 x 10(-7), 2.32 x 10(-7), 2.28 x 10(-7), 2.29 x 10(-7)mm(3)/N mm, respectively. The worn degree of the grinding surface is reduced, and the wear surface has a small amount of spalling and furrows. The wear mechanisms were three-body abrasive wear, slight adhesive wear and oxidative wear. In short, the strengthening and toughening mechanisms are ascribed to the grain refinement, load transfer effect and Zener pinning effect after heat treatment.