Designing grain refinement passes for multi-direction forging: A phase-field crystal study

Abstract

Multi-directional forging is an effective plastic deformation method for polycrystalline grain refinement, and the degree of refinement is closely related to the number of forging passes. However, the relationship between the degree of refinement and the number of forging passes is almost ambiguous. Focusing on the forging passes, the grain refinement and dislocation nucleation mechanisms were revealed by combining the free energy variation and the strain field distribution using the dual-mode phase-field crystal model in our work. The results show that the nucleated dislocations within the grain can divide the grain into many finer grains under continuous stress. The nucleation mechanism of dislocation mainly includes two forms: grain boundary emission dislocation and atomic misalignment near the twin boundary. The strain field distribution reveals the mechanism of dislocation annihilation. The grain refinement effect of triple pass stress loading is the best, being 59 %, 18 %, and 43 % higher than that of the one forging pass, two forging passes, and four forging passes stress loading respectively. Moreover, the cause of the above phenomenon was further revealed by atomic analysis. This study reveals the response rule of forging passes to fine grain strengthening and gives feedback to guide the actual production experiment.

Keywords

• Phase-field crystal method
• Polycrystalline
• Forging pass
• Grain refinement
• Dislocation