ABSTRACT
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 â¼30 GPa and 886 K, Ti-6Al-4V is found to be stable in the hexagonal-close-packed, orαphase. The effect of temperature on the volume expansion and compressibility ofα-Ti-6Al-4V is modest. The martensiticαâω(hexagonal) transition occurs at â¼30 GPa, with both phases coexisting until at â¼38-40 GPa the transition to theωphase is completed. Between 300 K and 844 K theαâωtransition appears to be independent of temperature.ω-Ti-6Al-4V is stable to â¼91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure-volume-temperature equations-of-state for theαandωphases of Ti-6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in theω-Ti-6Al-4V on decompression, with the hexagonal structure reverting back to theαphase at pressures below â¼9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4Vα-ß-ωtriple point to occur at â¼900 K and 30 GPa, in good agreement with our calculations.