Size Effect on Mechanical Properties and Deformation Behavior of Pure Copper Wires Considering Free Surface Grains.

Yu Hou,Xujun Mi,Zhen Yang,Lijun Peng,Haofeng Xie,Xue Feng,Guojie Huang,Wenjing Zhang

doi:10.3390/ma13204563

Abstract

The size (grain size and specimen size) effect makes traditional macroscopic forming technology unsuitable for a microscopic forming process. In order to investigate the size effect on mechanical properties and deformation behavior, pure copper wires (diameters range from 50 μm to 500 μm) were annealed at different temperatures to obtain different grain sizes. The results show that a decrease in wire diameter leads to a reduction in tensile strength, and this change is pronounced for large grains. The elongation of the material is in linear correlation to size factor D/d (diameter/grain size), i.e., at the same wire diameter, more grains in the section bring better plasticity. This phenomenon is in relationship with the ratio of free surface grains. A surface model combined with the theory of single crystal and polycrystal is established, based on the relationship between specimen/grain size and tensile property. The simulated results show that the flow stress in micro-scale is in the middle of the single crystal model (lower critical value) and the polycrystalline model (upper critical value). Moreover, the simulation results of the hybrid model calculations presented in this paper are in good agreement with the experimental results.

Highlights

With the rapid development of micro-electro-mechanical systems (MEMS) and their gradual application, the demand for micro-components is increasing
In plastic micro-forming technology, the size of the molded parts is less than 1 mm [1,2,3,4], with the crystal model ranged from single crystal to polycrystal
The results show that a decrease wire diameter leads of to pure a reduction in tensile investigated

Summary

Introduction

With the rapid development of micro-electro-mechanical systems (MEMS) and their gradual application, the demand for micro-components is increasing. Plastic micro-forming technology has a wide application prospect in the fields of micro-mechatronics, bio-medicine and micro-energy due to its advantages of simple processing, high efficiency, low cost, excellent mechanical properties, and good repeatability. In plastic micro-forming technology, the size of the molded parts is less than 1 mm [1,2,3,4], with the crystal model ranged from single crystal to polycrystal. As a result of the size effect, the forming quality and basic properties of the miniature parts are changed [5,6,7]. This change differs from the class of materials including crystalline and amorphous metals. Some literature mentions that materials have distinct critical size points, i.e., changes in mechanical properties at grain sizes less than

Results

Discussion

Conclusion