Effects of nitrogen on the mechanical behavior of hydrogenated V, Nb, and Ta
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I.
INTRODUCTION
T I - / p e m h f i t t l e m e n t n f V N h and Ta hv h v d r n v e n has b e e n attnouteu
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mechanisms involve the transport of hydrogen to a crack tip or to a stress concentrator, where a triaxial tensile stress field is produced. Consequently, kinetic arguments are not discriminating evidence for either mechanism. However, modification of the terminal solubility of hydrogen in these refractory metals might provide additional information that would improve our understanding of the pertinent factors responsible for the change in mechanical behavior resulting when hydrogen is present in V, Nb, and Ta. It has been demonstrated that some substitutional alloys of the refractory metals exhibit unusually high solubilities for hydrogen. ~~ In addition it has been shown that increasing the concentration of the other interstitials (C, O, and N) commonly found in V, Nb, and Ta greatly enhances the hydrogen solubility, tS-ls While considerable work has been done concerning hydrogen and its effect on mechanical behavior in substitutional alloys, l~ there is a lack of work dealing with the effect of hydrogen in combination with the other interstitials on the deformation behavior in V, Nb, and Ta. This paper examines the influence of nitrogen additions on the low temperature deformation behavior of hydrogenated V, Nb, and Ta.
lI.
MATERIALS AND PROCEDURES
The vanadium used in this investigation was in the form of chips which had been prepared by fused salt electrolysis. 22'23 These chips were consolidated into 15.9 mm diameter by 150 mm long "fingers" by arc-melting under purified argon. Ta and Nb were electron beam melted in order to reduce their oxygen and nitrogen contents before consolidating them into "fingers". Chemical analyses of all
W. A. SPITZIG, Senior Metallurgist, and C. V. OWEN, Associate Metallurgist, are with Ames Laboratory, Iowa State University, Ames, IA 50011. T. E. SCOTT, formerly with the Ames Laboratory, is Senior Metallurgist with ARCO Chemical Company, Route 6, Box A, Greer, SC 29651. Manuscript submitted May 28, 1985. METALLURGICALTRANSACTIONS A
three metals, as melted, and after the various charging procedures are given in Table I. amounts of nitrogen master alloys to the high purity material of interest during the arc-melting consolidation step. In order to insure a uniform composition, all alloy fingers were cold-swaged to 3.18 mm diameter rod, cut into short lengths, and remelted. Nitrogen analysis was performed on each test specimen after testing; the results indicated good homogeneity. The following fabrication schedule was employed for both the pure metals and the nitrogen alloys: 24 a. Cold swage 15.9 mm diameter ingots to 5.8 mm diameter. b. Anneal in vacuum at appropriate temperature for particular metal of interest. c. Cold swage to reduce rods 81 pet in area using three steps: 5.8 mm to 4.7 mm diameter, 4.7 mm to 3.8 mm diameter, 3.8 mm to 2.4 mm diameter. Following the final reduction the
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