Lattice expansion of Ti–6Al–4V by nitrogen and oxygen absorption

High temperature X-ray diffraction (HT-XRD) measurements have been performed on Ti-6Al-4V alloy to investigate the lattice changes induced by oxygen and nitrogen absorption. Experiments have been performed on stress-free powder for its high surface-volume ratio and to avoid possible effects on XRD patterns due to texture change and recovery of defective structures induced by measurement cycle in temperature. Cell parameters a and c, measured at increasing temperatures up to 600°C, show linear trends with different slopes. As temperature increases cell volume expands and c/a ratio changes. This is due to both lattice thermal expansion and absorption of oxygen and nitrogen. Part of gas remains entrapped in the metal after cooling to room temperature causing a residual lattice distortion. Results have been compared with literature data obtained in analogous tests performed on bulk material both in vacuum and inert gas atmosphere.