温变条件下金属细丝扭转反常塑性行为实验研究

In order to study the size effects and plastic recovery of micron-scale metallic wires at elevated temperatures, we plan to develop a new heating and temperature-control element based on the self-developed micro-torsion platform. We aim to study both size effects due to limitations by the grain size and due to nonuniform deformation, and their coupling effect, by preparing the wire samples with different diameter and of prescribed grain size. On the sample preparation, the metallic wires with diameter of 100μm are annealed under given conditions to obtain initial samples of different grain sizes. Afterwards, these samples are further electropolished for different time periods to obtain a series of new samples with diameter ranging from 8 to 100μm, but of the same grain size. These processes lay the foundation for the study of the size-dependent behavior of micron-scale metallic wires at elevated temperatures, which has not been carried out yet. On the other hand, we have found an anomalous plastic recovery in the cyclic torsion of micron-scale metallic wires at room temperature for the first time. The related work has been published in the top international journal Physical Review Letters. However, there have been no reports on the phenomenon of plastic recovery in the cyclic torsion of small-volume materials at elevated temperatures. In this project, we plan to perform the cyclic torsion tests on thin metallic wires which are heated in situ by passing an electrical current, and then analyze the relation between plastic recovery and temperature. This research may achieve the internationally recognized experimental results in this field for the first time.

以研究变温条件下微米级金属细丝反常塑性行为中的尺度效应、塑性恢复现象为目的，在自制的金属丝微扭转实验平台基础上，研制原位温度加载与控制单元。开展可控内部晶粒尺寸的超细金属丝试样的制备工作，以定量研究材料的晶粒尺寸效应与非均匀变形引起的尺度效应的耦合问题。在试样制备方面，将对100微米直径细丝进行热处理获取不同晶粒的原丝，然后通过电解减径制备出直径为8-100微米具有相同晶粒尺寸的细丝，为变温条件下的微米量级金属丝的尺度效应实验研究奠定基础。相关研究在国内外尚未成功开展，具有前瞻性。另外，课题组首次在微尺度金属丝常温下的循环扭转中发现塑性恢复现象，相关成果发表在国际学术期刊《物理评论快报》上，但目前还没有关于变温条件下微尺度材料在循环扭转中的塑性恢复现象的报道。本项目拟在金属丝通电加温的条件下，对金属细丝进行循环扭转实验，分析塑性恢复现象与温度之间的关系，争取获得学术界公认的创新性实验结果。

在微纳米尺度下，金属材料的弹塑性力学行为表现出与宏观尺度材料明显的差异。本项目对温变场下微尺度金属材料的反常塑性力学行为进行了深入的研究。主要成果包括：（1）在原微纤维扭转和拉伸试验机上结合可控温度箱，搭建了可控温微纤维扭转和拉伸试验平台。在温变场下对微尺度金属细丝进行了拉伸和扭转实验研究，探究温变场下微金属细丝力学行为的尺度效应。（2）研制了一台微尺度金属细丝电解装置，探索出了理想的电解液配方。通过电解减径成功制备出了具有相同晶粒尺寸不同外观尺寸的细铜丝试件。对此类试件进行扭转实验，研究了在排除内部晶粒尺寸的影响下，仅应变梯度效应对细丝扭转尺度效应的贡献。（3）在微纤维扭转试验机上，进行了微金属铜丝在室温下的扭转应力释放实验。系统研究了初始应力、外观直径、加载速率对细丝非均匀变形场下应力释放特性的影响。在可控温微纤维拉伸试验平台上，对微金属铜丝进行了温变场下拉伸应力释放实验，探究了初始应力、外观直径、温度场对细丝均匀变形场下应力释放特性的影响。（4）在循环扭转加载下，对微尺度铜丝的循环硬化和平均应力松弛行为进行了实验研究。同时探究了初始应变、应变幅值、晶粒尺寸对细丝平均应力松弛行为的影响。（5）进行了微尺度镍悬臂梁振动实验，探究其振动频率与微梁厚度间的关系。构建了相关理论模型，预测其弹性尺度参数。同时基于高阶梯度弹性理论结合经典梁理论，探究温度载荷、轴向速度影响下微尺度梁的屈曲、振动特性。在项目执行期间，在国际SCI期刊上发表论文23篇，获发明专利2项；参加学术会议21人次。培养博士生6名，其中3名已毕业，3名在读。