The significant impact of grain structure on large strain-rate sensitivity of ultrafine-grained low alloy steel under nanoscale deformation: Experimental and theoretical analysis-猫眼课题宝

纳米尺度变形下晶粒结构对超细晶低合金钢大应变率敏感性的显着影响：实验与理论分析

DOI：

10.1016/j.msea.2019.04.028

发表时间：

2019-05

期刊：

Mater. Sci. Eng. A

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

W.Y. Xue;Y.F. Shen

为了解超细晶结构(UFG)的应变速率敏感性，并与粗晶结构(CG)的应变速率敏感性进行了比较，结合使用聚焦离子束的纳米级变形区域的死后电子显微镜，进行了载荷控制的纳米级变形实验。UFG钢的晶粒度为∼530 nm，析出物为∼80 nm。屈服强度(σy)和极限拉伸强度(σUts)随着应变率从0.0015增加到0.15 S−1而显著增加，从而导致拉伸应变过程中的延伸率(ɛf)下降。纳米变形实验表明，随着应变速率的增加，硬度从3.0 2 ± 0.0 5 Gpa增加到3.36 ± 0.0 5 Gpa，正应变速率敏感性为0.025.5%的S−1，其应变速率敏感度大于CG对应的应变速率敏感值，与观察到的Bcccc金属中的现象形成鲜明对比。理论分析认为，∼25 b3(b-Burgers矢量)的小激活体积是超细颗粒和纳米析出物共同作用的结果，阻碍了位错的运动，导致了一种特殊的硬化行为，这是导致超细晶铁素体钢反常的表面张力和激活体积的原因。

Load-controlled nanoscale deformation experiments were carried out in conjunction with post-mortem electron microscopy of nanoscale deformation region involving the use of focused-ion beam, to obtain nanomechanical insights on the strain rate sensitivity of ultrafine grained structure (UFG) and compare with the coarse-grained (CG) counterpart. The UFG steel had a grain size of ∼530 nm and spherical precipitates of ∼80 nm. Both yield strength (σy) and ultimate tensile strength (σUTS) increased significantly with increased strain rate from 0.0015 to 0.15 s−1, with consequent decrease in elongation-to-failure (ɛf) during tensile straining. Nanoscale deformation experiments indicated an increase of hardness from 3.02 ± 0.05 GPa to 3.36 ± 0.05 GPa on increasing the strain rate from 0.05 to 0.5 s−1with positive strain rate sensitivity (SRS) of 0.025, which was larger than the CG counterpart and is in striking contrast to the observed phenomena inbccmetals. From the theoretical analysis, it is envisaged that the small activation volume of ∼25 b3(b-Burgers vector) is a consequence of combination of UFG and nanosized precipitates that prevented the movement of dislocations leading to a peculiar hardening behavior, which was responsible for the abnormal SRS and activation volume of UFG ferritic steel.