Pöhl Fabian
Ruhr-Universität Bochum, Chair of Materials Technology, Bochum, 44780, Germany.
Sci Rep. 2019 Oct 25;9(1):15350. doi: 10.1038/s41598-019-51644-5.
This study analyzes the elastic-to-plastic transition during nanoindentation of polycrystalline iron. We conduct nanoindentation (Berkovich indenter) experiments and electron backscatter diffraction analysis to investigate the initiation of plasticity by the appearance of the pop-in phenomenon in the loading curves. Numerous load-displacement curves are statistically analyzed to identify the occurrence of pop-ins. A first pop-in can result from plasticity initiation caused by homogeneous dislocation nucleation and requires shear stresses in the range of the theoretical strength of a defect-free iron crystal. The results also show that plasticity initiation in volumes with preexisting dislocations is significantly affected by small amounts of interstitially dissolved atoms (such as carbon) that are segregated into the stress fields of dislocations, impeding their mobility. Another strong influence on the pop-in behavior is grain boundaries, which can lead to large pop-ins at relatively high indentation loads. The pop-in behavior appears to be a statistical process affected by interstitial atoms, dislocation density, grain boundaries, and surface roughness. No effect of the crystallographic orientation on the pop-in behavior can be observed.
本研究分析了多晶铁纳米压痕过程中的弹塑性转变。我们进行了纳米压痕（贝氏压头）实验和电子背散射衍射分析，以通过加载曲线中出现的“弹出”现象来研究塑性的起始。对大量的载荷-位移曲线进行统计分析，以确定“弹出”的发生情况。第一次“弹出”可能是由均匀位错形核引起的塑性起始导致的，并且需要无缺陷铁晶体理论强度范围内的剪应力。结果还表明，预先存在位错的体积中的塑性起始受到少量间隙溶解原子（如碳）的显著影响，这些原子偏聚到位错的应力场中，阻碍了它们的移动性。对“弹出”行为的另一个强烈影响是晶界，晶界可导致在相对较高的压痕载荷下出现较大的“弹出”。“弹出”行为似乎是一个受间隙原子、位错密度、晶界和表面粗糙度影响的统计过程。未观察到晶体取向对“弹出”行为的影响。
