Effects of oxygen and hydrogen on tensile and internal friction properties of niobium-vanadium alloys

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Indrawirawan, Hendra
Iowa State University; Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Materials science and engineering; Metallurgy
thesis / dissertation description
The effect of additions of up to 10 at% vanadium on the oxygen Snoek peak in niobium was investigated by an internal friction technique. Vanadium-oxygen interaction peaks were identified at approximately 500 K and 650 K. For the Nb-0.24 at% V and the Nb-0.42 at% V alloys, at an oxygen/vanadium ratio greater than one, the 400 K unperturbed oxygen Snoek peak in niobium appears, thus providing strong evidence for oxygen trapping in these alloys. The 500 K peak is interpreted as a stress induced reorientation of oxygen associated with a single vanadium atom in a type n = 1 cell, whereas the 650 K peak is due to oxygen associated with two or more vanadium atoms in type n = 2 and n = 3 cells. The observed results are discussed in terms of the elastic and chemical interaction models for substitutional-interstitial solute interactions in a bcc lattice;Internal friction results do not provide evidence of an oxygen-hydrogen interaction. Hydrogen has no observable effect on the oxygen Snoek peak in unalloyed niobium and oxygen has no effect on the peak temperature or activation enthalpy for hydrogen relaxation in the Nb-10 at% V alloy;The effects of oxygen and hydrogen on the tensile properties of the Nb-10 at% V alloy were also studied. The addition of oxygen increases both the thermal and athermal stress components, although the effect is more pronounced on the thermal than on the athermal stress component. The 0.2% tensile yield stress is proportional to concentration as is predicted for a concentrated solid solution. For the Nb-10 at% V alloy containing hydrogen, alloy softening is observed at (TURN)125 K regardless of the presence of oxygen. This behavior is explained by the stress-induced ordering of hydrogen atoms in this temperature range. The effect of hydrogen on the strengthening and ductility of this alloy is much more pronounced in the presence of oxygen than in the low oxygen alloy.