The thermally activated deformation of niobium-molybdenum and niobium-rhenium alloy single crystals

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Measurements of the yield-stress and of the strain-rate sensitivity in compression over the temperature range 14-373°C are reported for single crystals of niobium of two purities and for niobium alloy single crystals containing up to 25 a/o molybdenum or 9 a/o rhenium. As the solute content increases, the maximum in the curve of strain-rate sensitivity versus temperature first decreases in magnitude and then moves to higher temperatures, and in the more concentrated alloys a second peak appears at lower temperatures. A corresponding inflection appears in the curves of yield stress versus temperature, and a similar temperature dependence of tho yield stress is also observed in ultra high vacuum annealed niobium. Analysis of the activation parameters indicates that there are two rate controlling mechanisms in different ranges of temperature. These processes occur in a parallel manner in such a way that, at constant strain rate, the mechanism requiring lowest stress is selected. It is therefore suggested that tho processes are similar in character but involve two separate saddle-point configurations which are affected by the additions of substitutional solute atoms. © 1972, Taylor & Francis Group, LLC. All rights reserved.

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Philosophical Magazine