The Plastic Deformation Mechanisms of hcp Single Crystals with Different Orientations: Molecular Dynamics Simulations

Abstract

The deformation mechanisms of Mg, Zr, and Ti single crystals with different orientations are systematically studied by using molecular dynamics simulations. The affecting factors for the plasticity of hexagonal close-packed (hcp) metals are investigated. The results show that the basal <a> dislocation, prismatic <a> dislocation, and pyramidal <c + a> dislocation are activated in Mg, Zr, and Ti single crystals. The prior slip system is determined by the combined effect of the Schmid factor and the critical resolved shear stresses (CRSS). Twinning plays a crucial role during plastic deformation since basal and prismatic slips are limited. The 101¯2 twinning is popularly observed in Mg, Zr, and Ti due to its low CRSS. The 101¯1 twin appears in Mg and Ti, but not in Zr because of the high CRSS. The stress-induced hcp-fcc phase transformation occurs in Ti, which is achieved by successive glide of Shockley partial dislocations on basal planes. More types of plastic deformation mechanisms (including the cross-slip, double twins, and hcp-fcc phase transformation) are activated in Ti than in Mg and Zr. Multiple deformation mechanisms coordinate with each other, resulting in the higher strength and good ductility of Ti. The simulation results agree well with the related experimental observation.

Evolution of Face-Centered Cubic Ti Alloys Transformation by X-ray Diffraction Profile Analysis in Mechanical Alloying

“…The α-Ti phase shows lower ρp values for all milling times than all other phases. This could be related to the activation of slip systems in the hcp crystal structure of the α-Ti phase and the store plastic deformation energy [97,102,[104][105][106][107]. For the β-Ti, the increment of ρp values could be related with transformation induced by deformation from α-Ti to β-Ti [33,34,41,43,96], indicating that the formation of this phase requires a high number of ρp to its formation below 30 h of MA.…”

Optimizing the Rolling Process of Lightweight Materials

“…HCP polycrystalline materials have limited deformation systems, which has a negative impact on material ductility. HCP structures are sensitive to the crystallographic texture because of their low symmetry and anisotropic behavior [19,20]. This results in a significant effect on texture evolution for HCP material during plastic deformation.…”

Machine learning for metallurgy V: A neural-network potential for zirconium

“…Due to the high stresses needed to activate ⟨c + a⟩ slip with deformation in the ⟨c⟩ direction, deformation twinning becomes operative in Zr (and other hcp metals) to provide further ⟨c⟩ -axis deformation. High twinning activity has been observed in Zr compared to less ductile hcp-metals such as Mg [20]. Fracture behavior involves the surface energies of all of these different possible cleavage planes and the blunting of cracks by dislocation emission on the various slip planes that intersect the crack front.…”