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

The effects of nitrogen and oxygen absorption on lattice expansion of Ti–6Al–4V have been investigated by high-temperature X-ray diffractometry. Experiments have been performed on stress-free powder for its high surface–volume ratio and to avoid possible effects on diffraction patterns due to texture change and recovery of defective structures induced by the measurement cycle at temperature. Cell parameters a and c, measured at increasing temperatures up to 600 °C, show linear trends with different slopes. As temperature increases, the cell volume expands and the c/a ratio changes. This is due to both lattice thermal expansion and absorption of oxygen and nitrogen. Part of the 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 Ti–6Al–4V alloy both in vacuum and in inert gas atmosphere.