In-situ tensile tests have been performed in a dual beam focused ion beam and scanning electron microscope on as-grown and prestrained single-crystal molybdenum-alloy (Mo-alloy) fibers. The fibers had approximately square cross sections with submicron edge lengths and gauge lengths in the range of 9-41 μm. In contrast to previously observed yield strengths near the theoretical strength of 10 GPa in compression tests of ~1-3-μm long pillars made from similar Mo-alloy single crystals, a wide scatter of yield strengths between 1 and 10 GPa was observed in the as-grown fibers tested in tension. Deformation was dominated by inhomogeneous plastic events, sometimes including the formation of Lüders bands. In contrast, highly prestrained fibers exhibited stable plastic flow, significantly lower yield strengths of ~1 GPa, and stress-strain behavior very similar to that in compression. A simple, statistical model incorporating the measured dislocation densities is developed to explain why the tension and compression results for the as-grown fibers are different.
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This work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (materials synthesis and modeling) and the Center for Defect Physics, an Energy Frontier Research Center supported by the Office of Basic Energy Sciences, U.S. Department of Energy (materials characterization and testing). GMP gratefully acknowledges the Alexander von Humboldt Foundation for fellowship support during the period in which the work was performed.
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Johanns, K.E., Sedlmayr, A., Phani, P.S. et al. In-situ tensile testing of single-crystal molybdenum-alloy fibers with various dislocation densities in a scanning electron microscope. Journal of Materials Research 27, 508–520 (2012). https://doi.org/10.1557/jmr.2011.298