Directional amorphization of covalently-bonded solids: A generalized deformation mechanism in extreme loading

MATERIALS TODAY

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Article

Zhao, S.^1,2  Li, B.³  Remington, B. A.⁴  Wehrenberg, C. E.⁴  Park, H. S.⁴  Hahn, E. N.³  Meyers, M. A.³ 

[1] Beihang Univ, Beijing, Peoples R China

[2] Univ Calif Berkeley, Berkeley, CA 94720 USA

[3] Univ Calif San Diego, San Diego, CA 92103 USA

[4] Lawrence Livermore Natl Lab, Lawrence, KS USA

关键词: Covalent bonding;    Shock compression;    Amorphization;    Materials under extreme conditions;    Peierls Nabarro stress;   

DOI  :  10.1016/j.mattod.2021.04.017

来源: Elsevier

【 摘 要 】

Shock compression subjects materials to a unique regime of high quasi-hydrostatic pressure and coupled shear stresses for durations on the order of 1-10 nanoseconds for laser-driven loading of samples. There is, additionally, an attendant temperature increase due to the shock and the mechanisms of plastic deformation in metals whereby dislocations, twins, and phase transitions nucleate and propagate at velocities near the sound speed. Covalently bonded materials have, by virtue of the directionality of their bonds, great difficulty in responding by conventional plastic deformation to this extreme regime of shock compression. We propose that the shear from shock compression induces amorphization, as observed in Si, Ge, B4C, SiC, and olivine ((Mg, Fe)2SO4) and that this is a general deformation mechanism in a broad class of covalently bonded materials. The crystalline structure transforms to amorphous along regions of maximum shear stress, forming nanoscale bands, and thereby relaxing the shear component of the imposed shock stress. This process is usually preceded by the emission and propagation of a critical concentration of dislocations.

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