Influence of Nonglide Stress on the Structure and Mobility of Pyramidal-I and -II ⟨c + a⟩ Edge Dislocations in Magnesium

Herein, molecular dynamics simulations were performed to investigate the structure and slip behavior of ⟨𝑐 + 𝑎⟩ edge dislocations on the pyramidal-I (Pyr-I) plane in magnesium (Mg), which were compared to those on the pyramidal-II (Pyr-II) plane. ⟨𝑐 + 𝑎⟩ dislocations on pyramidal planes are metastable and transition into sessile, typically sessile 〈 c 〉 and glissile 〈 a 〉 basal dislocations (basal-dissociated ⟨𝑐⟩ + basal ⟨𝑎⟩ ), or a dissociated ⟨𝑐 + 𝑎⟩ dislocation along the basal plane (basal-dissociated ⟨𝑐 + 𝑎⟩ and its derivative structure). This transition occurs at temperatures of >100 and >400 K for Pyr-I and -II ⟨𝑐 + 𝑎⟩ edge dislocations, respectively, in the absence of shear deformation along the slip direction, except under large non-glide stresses. The critical resolved shear stress (CRSS) of the slip plane where Pyr-I ⟨𝑐 + 𝑎⟩ edge dislocations glide at 10 K increases with increasing compressive or tensile strains normal to the slip plane and exhibits a minimum value of ~486 MPa. Similarly, the CRSS for Pyr-II ⟨𝑐 + 𝑎⟩ edge dislocations decreases with increasing compressive strains normal to the slip plane and exhibits a maximum value of ~149 MPa at 10 K. Our findings provide insights into the design of ductile Mg alloys.