Hydrogen and deuterium diffusion in vanadium-niobium alloys
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I.
INTRODUCTION
THE diffusion
of hydrogen has frequently been studied in pure, solute-free metals. The influence of substitutional alloying elements on hydrogen migration has been investigated far less often. Theoretical studies of interstitial diffusion in binary alloys have usually considered only those cases in which both the substitutional and interstitial concentrations are small. 1': Perhaps as a result of these theoretical limitations, experimental measurements of hydrogen migration in alloys have usually been restricted to systems containing dilute concentrations of both hydrogen and the substitutional alloying element. 4'5'6 Nevertheless, nondilute multicomponent alloys are often used in engineering applications and the migration of hydrogen in such systems may be of considerable practical impact. Further, diffusion studies as a function of alloy composition should be useful in better characterizing the hydrogen-substitutional atom interaction. In an earlier investigation, 7 the present authors studied the diffusion of hydrogen in vanadium-titanium alloys. However, titanium has a limited solubility in bcc vanadium at low temperatures. 8 In order to study diffusion across the entire range of alloy compositions in a binary system, the vanadium-niobium system was chosen for scrutiny. A number of interesting and practical incentives exist for the study of hydrogen diffusion in vanadium-niobium alloys. Miller and Westlake9 have shown that the terminal hydrogen solid solubilities can be very high in this system. No hydride was observed in a 50 at. pct Nb alloy with a hydrogen-to-metal atom ratio of 0.8, even when this alloy was cooled to liquid nitrogen temperatures. Thus, it appears possible to maintain high hydrogen concentrations in solution at intermediate substitutional alloy compositions even at low temperatures. Consequently, low-temperature diffusion studies are not hindered by low hydrogen concentrations. Hydrogen diffuses very rapidly in vanadium and in niobium so that experiments are possible in which the longrange diffusion of hydrogen is studied by analysis of macroscopic diffusion profiles, thus eliminating experimental complications arising from surface pemaeation barriers. D.T. PETERSON is Professor, Department of Materials Science and Engineering and Senior Metallurgist, Ames Laboratory--United States Department of Energy, Iowa State University, Ames, IA 50011. H.M. HERRO, formerly a Graduate Student, Department of Materials Science and Engineering, Iowa State University, is Senior Metallurgist at Nalco Chemical Company, Metallurgy Laboratory, 6216 West 66th Place, Chicago, IL 60638. Manuscript submitted August 30, 1985. METALLURGICAL TRANSACTIONS A
No systematic investigation of hydrogen diffusion has been done in vanadium-niobium alloys. One study4 showed little change in the rate of hydrogen migration when 1 at. pct niobium was added to pure vanadium. However, additions of even small amounts of titanium and zirconium to vanadium do materially decrease hydrogen diffusion rates. 4'7 Much sm
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