The effect of surface oxidation on hydrogen absorption in Ti-6Al-4V alloy studied by elastic recoil detection (ERD), X-ray diffraction and nanohardness techniques

Abstract

The effect of naturally occurring oxide and oxidised layers formed by ion implantation and thermal oxidation on hydrogen absorption was investigated in Ti-6Al-4V alloy samples as a possible candidate for hydrogen storage. The samples were implanted with two different oxygen fluences (1.5 × 1017 and 3.0 × 1017 ions/cm2) at room temperature and 550 °C, and comparison was made with thermally oxidised samples at a temperature of 550 °C for 2 h. All samples were afterwards hydrogenated at 550 °C for 2 h. The elastic recoil detection analysis show that approx.14 at.% H was absorbed in as-received and thermally oxidised samples. The native oxide layer and the oxidised layer formed by thermal oxidation enhanced the absorption of hydrogen regardless of their different thickness and stoichiometry. The amount of hydrogen, however, was significantly lower in implanted samples, approx. 3–5 at.%, suggesting that oxygen ions implanted in alloy prevent hydrogen absorption. It was found that the average amount of absorbed hydrogen within the projected depth was reduced due to implantation of oxygen ions regardless of their fluences and implantation temperature. The hydrides were not determined in any of investigated samples while the surface hardness of all samples increases after hydrogenation although to different extent.