The identification of hydrogen trapping states in an Al-Li-Cu-Zr alloy using thermal desorption spectroscopy

Abstract

Thermal desorption spectroscopy (TDS) was utilized to identify several metallurgical states in an Al2Li -2Cu-0.1Zr (wt pct) alloy, which trap absorbed hydrogen. Six distinct metallurgical desorption states for hydrogen were observed for tempers varying from the T3 to peakaged condition. Lower energy thermal desorption states were correlated with interstitial sites, lithium in solid solution, and ␦Ј (Al 3 Li) precipitates. These states have trap-binding energies Յ25.2 kJ/mol. Under the charging conditions utilized, approximately 4 pct of the total (e.g., trapped and lattice) hydrogen content was associated with interstitial sites, consistent with the view that the intrinsic lattice solubility of hydrogen in aluminum is very low. In contrast, dislocations, grain boundaries, and T 1 (Al 2 CuLi) particles were found to be higher energy-trap states with trap-binding energies Ն31.7 kJ/mol. Approximately 78 pct of all absorbed hydrogen occupied these states. Moreover, greater than 13 pct of the available trap sites at grain boundaries were occupied. Such a high hydrogen coverage at grain-boundary sites supports the notion that hydrogen contributes to grain-boundary environmental cracking in Al-Li-CuZr alloys. Also, it points out the error in assuming that hydrogen cannot play a major role in cracking of Al-based alloys due to the low lattice solubility.

Kinetics of Hydrogen Desorption from Rapidly Solidified Al-Cr Alloys

“…The trap site having the lowest binding energy (see peak 0 in the TDS spectra) is tentatively attributable to hydrogen in the interstitial lattice sites trapped by Cr atoms from literature. 24,25) The shifting of the first desorption peak in case of RS Al-Zr alloys to a lower temperature compared with RS pure aluminum provides further evidence and was determined recently.…”

“…2(a). The data of recognized peak temperatures T m and trap sites assigned from literature 7,17,18,24,25) as discussed later are summarized in Table 1. Note that TDS spectrum from RS foil of pure aluminum 17) shown also in Fig.…”

“…Meanwhile, hydrogen interactions with dislocations as well as vacancies are considered to contribute mostly to hydrogen embrittlement of aluminium materials. 3,9,25,30) The scope of this paper did not allow for a detailed comparison of the hydrogen-desorption-rate curves from RS pure aluminum with those reported for traditionally processed pure aluminum although references to the hydrogen tapping and evolution in conventional aluminium have been alluded to in the text. Figure 3 exemplifies thermal desorption spectra from pure polycrystalline aluminum 18) as well as aluminum produced by a DC cast rolling ingots.…”

Imaging and quantification of hydrogen isotope trapping.

“…The hydrogen isotope content in binary Al-4 wt.% Cu was several times higher than that of pure Al, although binary Al-Cu alloys generally have low hydrogen contents compared to those with elements that are known to trap more effectively (e.g. Mg and Li) [24]. The binding energy of H to Cu in solution has previously been bounded as <=0.05 eV [25].…”

“…The binding energy of H to Cu in solution has previously been bounded as <=0.05 eV [25]. Al-Cu GP-zones and precipitates have been observed by tritium autoradiography to trap hydrogen isotopes [26], but there have not been significant trap energies measured in Al-Cu binaries by TDS [24]. …”