Temperature and grain size dependences of mechanical properties of nanocrystalline copper by molecular dynamics simulation

Abstract

Nanocrystalline copper (Cu) is considered to be one of the best interconnected material in integration circuit (IC) industry, because of its ultra-low resistivity and high mechanical stability. Mechanical properties of nanocrystalline Cu are completely different from those of bulk monocrystalline Cu. These properties are of high importance in the assessment of the thermo-mechanical reliability of the interconnected IC structure. To investigate the effects of the grain sizes and temperature on the mechanical properties of nanocrystalline Cu, molecular dynamics simulations of uniaxial tensile test are performed in this study. The results show that the elastic modulus of nanocrystalline Cu with grain sizes of 4.65–12.41 nm gradually increases with the increase of the mean grain sizes, the corresponding flow stress concurrently increases, and the flow stress is proportional to the square-root of the grain size, which satisfies the inverse-Hall–Petch relation. Furthermore, the elastic modulus linearly decreases with the increase of temperature. The coupled effect of the flow stress, strain rate and temperature were elaborated by the Arrhenius hyperbolic sinusoidal model. Meanwhile, the deformation activation energy of nanocrystalline Cu for various grain sizes were obtained. All of the tensile simulation tests confirmed that the mechanism of plastic deformation for nanocrystalline Cu with 4.65–12.41 nm grain sizes is mainly specific to the grain boundary sliding and grain rotation. The dislocation nucleation and migration, which is usually the deformation mechanism of plasticity for macroscopic materials, is no longer the dominant factor for nanocrystalline Cu.

Investigation on the Mechanical Properties of Polycrystalline Mg Using Molecular Dynamics Simulation

“…The results showed that the stress-dominated deformation mechanism at grain boundaries is insensitive to strain rate, while stacking faults impede the movement of some dislocations, which leads to an increase in strain rate sensitivity. Chen et al [9] investigated the effect of strain rate on the mechanical properties of polyCu. The simulated results showed that the mechanical properties of polyCu were sensitive to high strain rates (1 × 10 9 s −1 ∼5 × 10 10 s −1 ), but the properties did not change much at low strain rates (5 × 10 7 s −1 ∼1 × 10 9 s −1 ).…”

Microstructure evolution and the deformation mechanism in nanocrystalline superior-deformed tantalum

“…As can be seen, the elastic modulus decreases with increasing temperature, which indicates an increase in the diffusion capacity of the atoms under external loading due to the thermally-reduced bond energy. 55,56 The higher the temperature, the lower the deformation resistance of the atom, which is manifested by a low elastic modulus. Furthermore, the slope of the elastic modulus–temperature curve is similar for NC-Ta with different average grain sizes, implying that the temperature dependence of the mechanical properties is not affected by the grain size.…”

Grain size responsive uniaxial tensile behavior of polycrystalline nanocopper under different temperatures and strain rates

“…It can be seen from Figures 4c and d that the grain boundaries are sliding from their original shape and shifting to newer formations. This mechanism is found to exist in previous studies as well (Li et al ., 2019; Jeon et al ., 2010; Chen et al ., 2019; Zhang et al ., 2020). This sliding of grain boundaries can be seen in Figures 4a and b where grain boundary between grain numbers 1 and 4 is found developing in the encircled region.…”