Study of the hydrogen internal friction peak in Nb-10 At. Pct V in the presence of oxygen
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INTRODUCTION
T H E effects of interstitial impurities on the strength and ductility of refractory metal alloys are of critical importance in such high temperature applications as controlled thermonuclear, fast breeder, or space nuclear reactors. The high solubility of Nb-V alloys for both oxygen and hydrogen makes them ideal materials for studying the effects of these interstitial solutions on the mechanical properties of the refractory metals, particularly of the combined (additive or synergistic) effects of these rather common impurities. The Nb-10 at. pct V alloy was selected for the present study because of its high solubility for hydrogen at ambient temperature and below. Owen e t a / . [1'21 discovered a broad internal friction peak due to hydrogen in the Nb-V alloys with a distribution of activation energies I3] whose mean corresponds closely to the activation energy for diffusion determined by the Matano methodJ 41 Presently, it is thought I2,31 that hydrogen occupies tetrahedral sites in the alloy, giving rise to a Snoek-type relaxation process. In these alloys, such jumps do not correspond to a single relaxation process, since a multitude of host environments exist, giving rise to a spectrum of activation energies. These observations immediately trigger the idea that if an interaction between hydrogen and oxygen should exist, the oxygen would have a pronounced effect on this hydrogen peak. Detailed studies of the effect of hydrogen on the oxygen Snoek peak in pure niobium and vanadium have been carried out recently, tSl In this case, there is clear evidence that at the temperature at which the oxygen peak is present, hydrogen does not interact with oxygen. Furthermore, it w a s f o u n d [6,71 that oxygen alone in niobiumrich alloys not only produces the oxygen Snoek peak tSl but also peaks associated with the trapping of oxygen either in the vicinity of individual vanadium solute sites L61 O. BUCK, Senior Metallurgist, is with the A m e s Laboratory, Iowa State University. H. I N D R A W I R A W A N , formerly Graduate Student at Ames Laboratory, is living in Indonesia. O.N. CARLSON, Professor Emeritus, is with the Department of Materials Science and Engineering and A m e s Laboratory, Iowa State University, A m e s , IA 50011. Manuscript submitted July 5, 1988. METALLURGICAL TRANSACTIONS A
or at clusters of two or three vanadium atoms, t7~ The latter case clearly applies to the Nb-10 at. pct V alloy. Effects of hydrogen on the V-O interstitial peaks would not be expected, since the peaks are so high in temperature that hydrogen would not be trapped by oxygen at these temperatures. On the other hand, studies on the effects of oxygen on the hydrogen peak t2,31 are feasible and even highly desirable due to the low temperatures of the hydrogen peaks. This enables the study to be performed in a temperature regime in which the mechanical properties are drastically affected by both oxygen and hydrogen. Investigations on the effects of oxygen and hydrogen on selected mechanical properties of Nb-10 at. pct
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