Novel Mechanisms for the Formation of Dislocation Cell Patterns in BCC Metal

Dislocation patterns and cell wall formation are key to understanding the mechanical properties of the materials in which they spontaneously arise, and yet the processing and self-assembly mechanisms leading to their formation continue to baffle experts. Tantalum subjected to shock loading has radical changes to its microstructures as function of grain orientation: cell walls are found in grains oriented in &lt;001&gt; but are suppressed in grains with &lt;011&gt; orientation. Here we use transmission electron microscopy (TEM) and discrete dislocation dynamics (DDD) to demonstrate a new mechanism that is key to the pattern-formation process: a coupling reaction between pseudo-dipolar mixed dislocations.<br/>We present the first large-scale DDD simulations exhibiting self-organization of dislocation networks into cell walls in deformed BCC metal (Tantalum) persisting at strain 20%. The simulation analysis captures several important features of the dislocation cell pattern effect observed in experiments.