540 / 2019-03-20 10:55:31

Strengthening Enhancement at the Lower Nanoscale

nanometal; materials strengthening; high pressure

全体主题 > High Pressure Physics and Materials Science

The mechanical strengthening of metals has been a long-standing challenge and topic of materials science in academia and industry. Strengthening of polycrystalline metals based on grain refinement is reportedly no longer effective below a critical grain size of about 10-15 nm, which puts a grain size limitation on making strong materials. Herein radial diamond-anvil cell X-ray diffraction techniques track in situ the yield stress and deformation texturing of pure nickel samples with various average grain sizes. Continuous strengthening is observed from 200 nm to the minimum grain size of 3 nm. Strengthening as a function of grain size is even enhanced in the lower grain size regime below 20 nm. We achieved a record high strength of ~5 gigapascals in nickel. The ultimate strength of 3 nm nickel reaches 13.5 gigapascals, approaching the theoretical “ideal” strength of solids, E/(10-20) (here E is the Young’s modulus). This breakthrough in materials strengthening is achieved by enhancing dislocation slip processes (both partial and full dislocations) as well as refinement by deformation twins, while at the same time suppressing grain boundary plasticity. The high strengths observed in 3 nm are caused by the superposition of strengthening mechanisms: partial and full dislocation hardening plus boundary strengthening. Ultrahigh strength of materials can be potentially achieved through size strengthening, a significant advance for industrial applications of nanomaterials.