The effects of interstitials and hydrogen-interstitial interactions on low temperature hardening and embrittlement in V,
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I.
INTRODUCTION
EARLIER work evaluated the effects of N t and 02 on the strength and ductility of hydrogenated V, Nb, and Ta. This paper completes this previous work by analyzing the effects of C on the mechanical behavior of hydrogenated V, Nb, and Ta and by comparing the relative effects of C, N, and O on low temperature hardening and embrittlement of these metals.
II.
MATERIALS AND PROCEDURES
The refining and processing of the V, Nb, and Ta used in this study have been described previously. ~ Alloys were prepared by adding different quantities of C master alloys to high purity V, Nb, or Ta during the arc-melting consolidation process. Chemical analyses on test specimens subsequent to testing indicated good homogeneity of the C alloys. Chemical analyses of the V, Nb, and Ta after melting and of the C alloys with and without hydrogenation are shown in Table I. The hydrogen charging treatment was the same as that described previously) The grain sizes of the pure V, Nb, and Ta and the C alloys are given in Table II. Also included in Table II are the grain sizes of N and O alloys of V, Nb, and Ta that were previously tested. ~.2 In all cases, but especially in V and Ta, the C alloys had a much smaller grain size than the pure metals as a result of using similar annealing treatments for the pure metals and the carbon alloys. ~The appreciable difference in grain size between the pure metals and the C alloys is most likely the result of fine carbide particles retarding grain growth because of the very low solubility of carbon in V, Nb, and T a : W. A. SPITZIG, Senior Metallurgist, and C. V. OWEN, Associate Metallurgist, are with Ames Laboratory, Iowa State University, Ames, IA 5001 I. T. E. SCOTT, formerly with Ames Laboratory, is Director, Institute of Materials Processing, Michigan Technological University, Houghton, MI 49931. Manuscript submitted July 30, 1985.
METALLURGICAL TRANSACTIONS A
Metallographic examination confirmed that fine carbide particles were present in the carbon alloys. However, these carbides did not appear to have much influence on the mechanical behavior of the hydrogenated alloys. Tensile tests were run at an initial strain rate of 8.3 x 10-5 s -1. Constant temperature liquid baths were used for test temperatures below 295 K. All test specimens were quenched to the test temperature to avoid changes in hydride morphology that could arise because of differences in the cooling rate) Reduction of area was used as the criterion for ductility and was determined from pictures of the fracture surfaces using a polar planimeter. The metallographic and torsion pendulum procedures used to monitor hydride formation and to determine the hydride solvus temperature have been described previously. 3 The temperatures reported as the hydride precipitation temperatures were obtained during cooling because this represented actual testing conditions.
III.
EXPERIMENTAL RESULTS
A. Effects of C and Combined C and H on Yield Stress The effects of C and combined C and H on the temperature dependence of the yield
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