Corrosion resistance of tantalum base alloys. Elimination of hydrogen embrittlement in tantalum by substitutional alloying

Abstract

Abstract The corrosion behaviour of substitutional Ta–Mo, Ta–W, Ta–Nb, Ta–Hf, Ta–Zr, Ta–Re, Ta–Ni, Ta–V, Ta–W–Mo, Ta–W–Nb, Ta–W–Hf and Ta–W–Re alloys has been investigated in various corrosive media, i.e. (1) concentrated sulfuric acid at 250°C and 200°C, (2) boiling hydrochloric acid of azeotropic composition, (3) concentrated hydrochloric acid at 150°C under pressure, (4) HF‐containing solutions and (5)0.5% H 2 SO 4 at room temperature (anodisation). In highly corrosive media such as concentrated H 2 SO 4 at 250°C and concentrated HCl at 150°C tantalum is hydrogen embrittled, probably by stress induced precipitation of β‐hydride. Both corrosion rate and hydrogen embrittlement in concentrated H 2 SO 4 at 250°C are strongly influenced by alloying elements. Small alloying additions of either Mo or Re decrease the corrosion rate and the hydrogen embrittlement, while Hf has the opposite effect. Hydrogen embrittlement in concentrated H 2 SO 4 at 250°C is completely eliminated by alloying Ta with 1 to 3 at % Mo (0.5 to 1.5 wt % Mo). These results can be explained in terms of the oxygen deficiency of the Ta 2 O 5 film and the electronic structure of these alloys.