Viewpoint on the Formation and Evolution of Annealing Twins During Thermomechanical Processing of FCC Metals and Alloys

This paper addresses the unresolved question of the formation mechanism of annealing twins in face-centered cubic (FCC) metals and alloys, despite the long-standing recognition of these defects. A review of various proposed mechanisms reveals that while many focus on coherent twin boundaries, incoherent twin boundaries are also prevalent, particularly in recrystallized microstructures, warranting further investigation. The paper discusses the significant differences in twin topologies that emerge following recrystallization and grain growth, suggesting distinct terminology be implemented rather than the broad term 'annealing twins.' Given the importance of twins in grain boundary engineering, the paper delves into the mechanisms that facilitate the formation of an interconnected network of twin and related boundaries, based on current knowledge of the processes involved. Additionally, the paper presents the state of the art in mesoscopic models and simulations that account for twin boundaries, highlighting the necessity of incorporating twins in understanding microstructure evolution during thermomechanical processing and its impact on material behavior. The dual role of twins, influencing material properties positively or negatively, is emphasized as a vital consideration in materials science.