Effects of hydrogen on mechanical properties of vanadium-niobium alloys
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I.
INTRODUCTION
REFRACTORY metals and alloys possess several desirable properties which make them candidates as first wall materials for controlled thermonuclear reactors. They can be readily fabricated, they have excellent mechanical properties over a wide temperature range, and they are resistant to radiation damage. On the other hand, it is known that hydrogen and its isotopes, always present in such reactors, may cause severe embrittlement of these metals and alloys. The physical and mechanical properties of V-Nb alloys have been well documented/-9 but little work has been performed on the effects of hydrogen on these properties. Eustice and Carlson 6 demonstrated that ductile-to-brittle transition temperature (D-BTT) of these alloys increases with increasing hydrogen content at a constant alloy composition and that at a constant hydrogen concentration the embrittlement could be mitigated by increasing the Nb concentration. In addition, Sasaki and Amano t~showed that the addition of 5 at. pct vanadium to niobium increases the hydrogen solubility limit; yet, this alloy exhibited a catastrophic loss in reduction of area at approximately 195 K when I at. pct of hydrogen was added. Miller and Westlake H studied extensively the terminal hydrogen solubility for the V-Nb system. They reported that, whether vanadium is added to niobium or vice versa, the solubility for hydrogen increases sharply and nearly linearly with metal solute concentration to a maximum in excess of 30 at. pct at the 50V-50Nb composition. In view of the high solubili.ty for hydrogen in these alloys, it is very surprising that some are embrittled by small additions of hydrogen in solid solution. This investigation was undertaken to characterize systematically any embrittlement found across the V-Nb alloy system and to try to determine the embrittlement mechanism caused by the hydrogen. Embrittlement was evaluated by losses in the reduction in area after the specimens containing hydrogen were fractured in tension. C.V. OWEN, D.-S. CHEONG, and O. BUCK are with Ames Laboratory-US DOE, Iowa State University, Ames, IA 50011. T.E. SCOTT is with Anaconda Aluminum Technical Center, Schaumburg, IL 60195. Manuscript submitted May 11, 1982.
METALLURGICALTRANSACTIONS A
II.
MATERIALS AND PROCEDURES
Double-electrorefined vanadium, obtained from the United States Bureau of Mines, ~2'~3 was employed. The niobium, obtained from Fansteel Corporation, was 99.9 pct pure. The latter material was further purified by electron beam melting before being alloyed with the electrorefined vanadium. Alloys of the following compositions were prepared by arc-melting under purified argon: 10, 25, 50, 75, 85, and 90 at. pct Nb. In addition, arc-melted ingots of pure V and Nb were prepared. All of the arc-melted materials were in the form of finger-shaped ingots..Chemical analyses from both ends of each ingot showed that the actual and intended compositions were nearly the same, as expected. The 14 mm diameter as-cast alloy ingots were encapsulated in stainless steel and redu
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