Preparation Of Electropolished Microscale Copper Wires And Experimental Study On Size Effect

With the development of science and technology, there is an increasing interest in the study of the mechanical behavior of materials at the micro/nano-scale. The size effect is observed in this scale which is different from the classical mechanics. Many researchers have done a lot of jobs to study it. However, there are many factors that affect the size effect, mainly including diameter and grain size. So, how to divide them to study each other attracts more and more to pay attention, which is also one of the most difficult problems.Commercial Cu wires of high purity(99.9%) with diameters of 50 um have been used. To obtain different wire diameters while keeping the average grain size constant, the wires were first electropolished for different time. Then, tensile and torsion experiments were conducted using these wires on the machines designed by research group. According to the experimental data, the diameter, grain size and strain gradient have been discussed. The main research contents and results are as follows:1. An experimental platform for electrolysis is designed and set up. Then, different wire diameters were obtained using the platform after choosing the correct process parameters. In order to determine the grain size, the wire cross-section was got by focused-ion beam(FIB). Also, the diameter was measured by scanning electron microscope(SEM). It is proved that the microscale copper wires with the same grain size can be prepared by using electrolytic polishing. At the same time, the rule of the diameter how to change was explored when time has changed.2. Tensile and torsion experiments were performed on the microscale copper wires whose diameters ranged from 20?m to 50?m. It is found that the yield strength remains basically unchanged when the diameter is different. So, the size effect is not observed in the tensile experiments. However, in the torsion experiments, the strong size effect is observed which reveals that the yield strength increases with decreasing the diameter.3. Tensile experiments were performed on the copper wires with different gauge length. It is found that there is no evidence which shows that the gauge length has an effect on the yield strength and tensile strength.4. According to the strain gradient plasticity theory, the material length scale l is got by using the tensile and torsion data fitting. As a result, the material length scale l is 3?m.