Effects of Trace Reinforcements on Microstructure of TC18 Titanium Matrix Composite

Ti-5Al-5Mo-5V-1Fe-1Cr titanium matrix composites reinforced with different mass fractions of TiB and TiC were fabricated via a consumable vacuum arc-remelting furnace. The reinforcements can significantly refine β phase during heat treatment. However, the extent of the microstructure refinement decreases gradually with the increase of the reinforcements. It is revealed that the microstructural phenomenon is associated with Zener dragging force exerted by the reinforcements. The increase rate of the dragging force tends to decrease with the increase of the reinforcements. Additionally, the effects of the reinforcements on the spheroidization of α were also investigated. The spheroidization rate of α fluctuates somewhat with increasing the trace reinforcements during heat treatment. Nevertheless, the reinforcements accelerate the spheroidization of α lath in the Widmannstatten structure obviously during isothermal compression. The effects of the reinforcements during isothermal compression are different from those during heat treatment. In addition to accelerating the diffusion significantly, the trace reinforcements also contribute to the spheroidization of α by accelerating interface transformation during isothermal compression.