The phase diagram of Ti-6Al-4V at high-pressures and high-temperatures.

We report results from a series of diamond-anvil-cell synchrotron x-ray diffraction and large-volume-press experiments, and calculations, to investigate the phase diagram of commercial polycrystalline high-strength Ti-6Al-4V alloy in pressure-temperature space. Up to ∼30 GPa and 886 K, Ti-6Al-4V is found to be stable in the hexagonal-close-packed, orphase. The effect of temperature on the volume expansion and compressibility of-Ti-6Al-4V is modest. The martensitic→(hexagonal) transition occurs at ∼30 GPa, with both phases coexisting until at ∼38-40 GPa the transition to thephase is completed. Between 300 K and 844 K the→transition appears to be independent of temperature.-Ti-6Al-4V is stable to ∼91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure-volume-temperature equations-of-state for theandphases of Ti-6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in the-Ti-6Al-4V on decompression, with the hexagonal structure reverting back to thephase at pressures below ∼9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4V--triple point to occur at ∼900 K and 30 GPa, in good agreement with our calculations.