摘要
The stability of Cu with different average grain sizes prepared by surface mechanical grinding treatment were investigated under the conditions of isothermal annealing and uniaxial tension.In both conditions,experimental results revealed that the stability of the grains decreased with the decrease of grain size when the grain size was above 70–75 nm,while the stability of the grains increased with the decrease of grain size when the grain size was below 70–75 nm.The grains of about 70–75 nm in size showed the worst stability in both thermal and mechanical conditions due to having the highest level of average atom free energy and their large amount of high energy grain boundary with large curvature.This size was very close to the calculated smallest size achievable by severe plastic deformation based on the grain refinement mechanism of dislocation evolution under present processing condition,at which both the highest density of dislocation and highest energy should be produced and induces poor stability.Below 70 nm,the deformation mechanism of nanograined Cu was transformed into a partial dislocation motion,which activated mechanically induced grain boundary(GB)relaxation accompanied by GB flattening and GB energy decrease and resulted in enhanced stability.This discovery offers the potential for developing nanograined metals with high strength and high stability.
基金
supported by the Ministry of Science and Technology of China(Grant Nos.2017YFA0204401 and No.2017YFA0700700)
the Chinese Academy of Sciences(Grant No.ZDYZ201701)
the Liaoning Revitalization Talents Program(Grant No.XLYC1808008).
