Non-Coplanar Dislocation Interaction Strengths And Their Correlation With Forest Dislocation Density In Magnesium

In addition to self-hardening induced by dislocation slip,latent hardening induced by the interaction of dislocations between different slip systems plays a fundamental role in strain hardening of metal materials.An accurate description of the hardening effect induced by dislocation interactions is an important basis for building a single crystal hardening model.Discrete dislocation dynamics（DD）can be applied to investigate the motion and interaction of a large number of dislocations and reveal the physical mechanism during crystal plastic deformation,while overcoming many difficulties in experimental research.It has become an effective tool for studying the plastic deformation behavior of crystal materials at the mesoscopic scale and constructing the multi-scale model of crystal plasticity.In this study,non-coplanar interactions between basal,prismatic and first-order pyramidal<a>dislocations in magnesium are investigated..DD models with different initial forest dislocation densities(ρ_f0=0.5×10¹²m^-2～10¹³m^-2)are constructed to simulate the interaction of the dislocations on specific slip systems.Based on the resolved shear stress of the primary slip system under different forest dislocation densities,different Taylor-type equations are employed to analyze the interaction coefficient and its change with the dislocation density.A special attention is paid to the influence of the lattice friction stress considered in the analyses on the interaction coefficients.The strength differences between the various dislocation interactions and their underlying mechanisms are discussed in conjunction with the dislocation configuration characteristics.The main conclusions are as follows:（1）Under the considered range of forest dislocation density,the modified Taylor equation can fit well the change of the simulated critical resolved shear stress with forest dislocation density（（?） data）,thus reflecting the basic tendency of decreasing interaction strengths with increasing forest dislocation density.（2）The interaction coefficients obtained by fitting the simulated data with the modified Taylor equation assuming the friction stress equal to the lattice friction indicate strong anisotropy and asymmetry in the strengths of different dislocation interactions.Collinear basal/prismatic interaction is the strongest,and non-collinear prismatic/basal interaction is the weakest.The non-collinear interactions between basal and prismatic dislocations show the most significant strength asymmetry.（3）The relative strength of collinear and non-collinear interaction in magnesium varies with the slip mechanism.Interaction pairs involving basal dislocations show the characteristics that collinear interaction is stronger than the corresponding non-collinear interaction,while other interaction pairs show the opposite.The primary dislocations developed in collinear interactions are generally shorter than those in non-collinear interactions,and a large amount of dislocation junctions or crossed states are formed in the latter ones.The nature of junctions is an important factor that affects the strength relationship between collinear and non-collinear interactions.（4）Test simulations of basal/prismatic and prismatic/basal interactions with different lattice friction values for the basal dislocations show that,the value of lattice friction has an important influence on the strength and relative magnitude of collinear and non-collinear interaction.An increase in the basal lattice friction leads to significantly increased average length of the primary dislocations in collinear interactions,and decreased number and average length of the junctions formed in non-collinear interaction.