Network-Strengthened Ti-6Al-4V/(TiC+TiB) Composites: Powder Metallurgy Processing and Enhanced Tensile Properties at Elevated Temperatures

Starting with graphite, TiB₂, and Ti-6Al-4V powders, the present work demonstrated that hybrid (TiC+TiB) network-strengthened Ti-6Al-4V—based composites can be fabricated via an integrated low-energy ball-milling and reaction hot-pressing-sintering technique. With the aid of phase equilibrium and powder densification kinetic calculations, the corresponding sintering parameters were optimized and tunable network microstructures were subsequently achieved. Tensile properties for these composites were examined at elevated temperatures of 500 °C, 550 °C, 600 °C, and 650 °C, the results of which indicated that the 50-μm network configuration with 5 vol pct reinforcer content led to the most enhanced tensile strength compared to both Ti-6Al-4V alloys and solely TiB-reinforced Ti-6Al-4V composites. The underlying strengthening mechanisms were mainly ascribed to carbon interstitial dissolution, reinforcer-assisted grain refinement, and extensive dispersoids. It was recognized from fractographic analyses that the matrix/reinforce interface contributed to the major crack propagation source at temperatures below 550 °C, leading to brittlelike fracture along the network boundary; however, once testing temperatures rose above 600 °C, matrix tearing and reinforcer cut-through mechanisms took place, giving rise to ductile fracture. Based on the experimental observations and theoretical calculations, future perspectives regarding the processing and microstructural manipulation for advanced high-temperature titanium matrix composites were also discussed.