Abstract
The effects of dissolved hydrogen on the yielding of polycrystalline tantalum have been studied in the temperature range between 78K and 373K. Tensile tests were performed at strain rate 1.7 × 10-4 s-1 on hydrogen-free specimens as well as specimens containing 30 to 70 ppm wt.H. The results show that addition of 30 to 160 ppm wt.H to polycrystalline Ta results in alloy softening which is reversed to a strengthening effect at lower temperatures. Both the softening and the strengthening effects are found to increase as the amount of dissolved hydrogen is increased. Analysis of results suggests that solute-dislocation interactions are the main contributors to the softening and the strengthening behavior in Ta-H alloys. The mechanisms suggested for solute-dislocation interactions differ at different temperature ranges, and involve dislocation-Cottrell mechanism at higher temperatures, dislocation-Snoek mechanism as temperature is lowered and dislocation-breakaway mechanism as temperature is further decreased.
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