Polymorphism and thermoelasticity of additively-manufactured Ti-6%Al-4%V: Insights from high-pressure X-ray diffraction measurements

The lightweight, high-strength, corrosion resistant titanium alloy Ti-6%Al-4%V (Ti64) is used in diverse technological applications, ranging from aeronautical engineering to consumer electronics and medical technologies. The phase diagram of Ti64 is qualitatively similar to that of pure Ti, however the transitions to the hexagonal (ω) and cubic (β) phases occur at higher pressure and temperature, respectively. Additive manufacturing (AM) is a production technique valued for its ability to produce features that are difficult or impossible to achieve with conventional methods. However, AM processes are known to affect the microstructure and mechanical properties of materials and parts. Understanding the “process-structure-properties-performance” relationship of AM parts is a critical step in designing and fabricating parts using these techniques. Using synchrotron X-ray diffraction data from diamond anvil cell measurements, we explore the effects of AM on the phase diagram and equation of state (EOS) of Ti64. At ambient temperature, we observe the α→ω transition in AM Ti64 is offset to slightly higher pressures, initiating between 35-38 GPa as opposed to 33 GPa. Furthermore, the α+ω mixed phase regime in the AM Ti64 was observed to extend over a larger pressure range: 16-18 GPa as opposed to 12 GPa. In addition to the pressure-temperature phase diagram, thermal EOS parameters will also be presented.