Boron carbide nanopillars under impact loading: Mechanical response and amorphous bands formation mechanism

XM Li and XY Yang and H Mei and LS Liu and S Xu and JY Zhang, COMPUTATIONAL MATERIALS SCIENCE, 214, 111746 (2022).

DOI: 10.1016/j.commatsci.2022.111746

The response of nanopillar to impact loading is significantly different from that of plate materials. To investigate the deformation behavior and mechanism of boron carbide nanopillars, molecular dynamics simulation is per-formed to simulate the impact of (B11CCBC)-C-p nanopillars at various velocities along c-axis (0001), b-axis ((1)over bar 2(1)over bar0) and d-axis ((11)over bar20) at room temperature. It is found that the impact response of (B11CCBC)-C-p nanopillars presents significant anisotropy. No obvious twin formation is observed during all impact processes. The critical impact velocity to destroy the (B11CCBC)-C-p crystal structure is 1.7 km/s along c- and b-axes, while along d-axis is slightly higher, 1.9 km/s. The plastic wave front appears in the waveform curve, when the impact velocities along the above directions are 1.9, 1.8 and 2.2 km/s, respectively. The U-s-U-p relationship along all directions shows a linear relationship, while the U-s-U and U-p-U relationships are bilinear. The damage of (B11CCBC)-C-p nanopillar under impact is accompanied by a significant adiabatic temperature rise, but critical temperatures could be below its melting point. The (B11CCBC)-C-p nanopillar impacted in different directions form abundant amorphous bands along specific crystal planes. The formation of amorphous band of (B11CCBC)-C-p nanopillars under impact loading condition is dislocation-mediated. Under all three impact conditions, new aslant bonds are formed between icosahedrons, causing dislocations to start nucleating. Then, the ( B11Cp) groups that lose the cage structure are further disordered resulting in that the dislocation region extends aslant through the nano-pillars under shear stress, eventually forming amorphous bands in dislocation region.

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