Nature of creep deformation in nanocrystalline Tungsten

S Saha and M Motalab, COMPUTATIONAL MATERIALS SCIENCE, 149, 360-372 (2018).

DOI: 10.1016/j.commatsci.2018.03.040

Because of Tungsten's (W) use in high temperature and stress environments like next generation fusion reactors, exploring the creep deformation mechanism in this material is very essential. In this work, for the first time, nature of creep in nanocrystalline (nc) Tungsten and factors that govern the creep mechanism like grain size, temperature, and applied stress are studied through atomistic simulations. Applied stress is varied from 2.5 to 5.5 GPa on the metallic sample while the temperature is varied in the range of 1600-2200 K. Stress and temperature variance are repeated for average grain sizes of 2.38 nm, 2.86 nm, 3.57 nm, and 4.76 nm. From the simulations, it has been found that the creep mechanism in nanocrystalline Tungsten is contingent on the applied stress as the creep mechanism varies from lattice diffusion to grain boundary diffusion creep even up to dislocation-creep. Moreover, temperature and grain refinement seem to aid the creep phenomenon at nanoscale. For very large value of stress and temperature, the power-law fails to define the creep in nc-Tungsten. In order to quantify the propensity and mechanism of creep in nanocrystalline Tungsten, stress and grain size exponents are observed in addition to the time evolution of strain and mean square displacement. Finally, atomistic features of deformation are analyzed which evince the simulation results.

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