Abstract
The effects of sample size and grain size on the surface morphology and flow stress of deformed samples were investigated by means of copper micro-cylinder compression experiments at room temperature. The results of SEM showed that when the grain size increased or the sample size decreased, the deformation non-uniformity of samples’ free surfaces increased. Meanwhile, the stress–strain curves showed that during the compression process, the flow stress of the sample also tended to decrease as the grain size increased or the sample size decreased. According to the experimental results of nanoindentation, a surface transition layer model was established on the basis of the surface layer model by considering the mutual constraint of grains and the existence of transition layer grains. The experimental results indicated that the stress–strain curve calculated by the surface transition layer model can more accurately reflect the actual deformation situation of the material compared to the surface layer model.
Highlights
In recent years, with the increasing demand for processing micro-parts, the micro-plastic forming process has developed rapidly as an important processing method in the microscopic field
The tensile test results of Zr65 Ni35 amorphous alloy films with sub-micron thickness by Matteo et al [5] suggested that yield stress increases with decreasing sample size
In order to study the effect of grain size on the results of compression tests, three different heat treatment processes were used to treat the original Ø6 rods × 20 rods to obtain different average grain sizes
Summary
With the increasing demand for processing micro-parts, the micro-plastic forming process has developed rapidly as an important processing method in the microscopic field. Due to the size effect, there are marked differences between the micro-forming process and the macro-forming process in terms of forming mechanism, material deformation law, and friction phenomenon. Structural parameters, physical parameters, and process parameters in macro-forming cannot be scaled down to the micro-forming process [1,2,3,4]. A large number of studies have been carried out by scholars for the size effect in the micro-forming process of crystalline and amorphous materials. The tensile test results of Zr65 Ni35 amorphous alloy films with sub-micron thickness by Matteo et al [5] suggested that yield stress increases with decreasing sample size. The compression test results of metallic glass pillars on a sub-micron scale by Greer et al [6]
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