Review on Microstructure Evolution of Metallic Materials Induced by Severe Plastic Deformation during Ultrasonic Surface Rolling

The ultrasonic surface rolling process (USRP) represents an emerging surface strengthening technique within the realm of severe plastic deformation (SPD). Owing to its remarkable merits in enhancing surface integrity, fatigue resistance, corrosion resistance, and wear resistance, USRP has garnered considerable attention. This discussion encapsulates the fundamental essence of surface integrity, provides a succinct introduction to the principles and benefits of USRP, and subsequently undertakes a comparative and analytical evaluation of plastic deformation attributes and constraints across various SPD methodologies. The advancement of USRP in influencing the microstructural evolution of surfaces via SPD is the focal point of this review. A plethora of investigations have underscored that among the mechanisms of plastic deformation, dislocation slip and deformation twinning emerge as the most prevalent contenders during the grain refinement progression of coarse-grained metallic materials. It is noteworthy that the plastic deformation mechanisms diverge due to dissimilar stacking faults and crystal structures inherent in different metal materials. Classified according to the plastic deformation mechanisms, this discourse delves into the realm of face-centered cubic (FCC) metal materials, delineating the prevalence of the dislocation slip mechanism for grain refinement in materials with elevated stacking fault energy. Middle-level FCC metal materials, under typical deformation conditions (e.g., room temperature, low stress, low strain rate), predominantly undergo dislocation slip as the primary plastic deformation mechanism. In contrast, under extreme deformation conditions (e.g., low temperature, high stress, high strain rate), deformation twinning takes precedence. For FCC metal materials characterized by low stacking fault energy, a coupling of deformation twin and dislocation slip mechanisms orchestrates the plastic deformation. In the context of body-centered cubic (BCC) metal materials, where the stacking fault energy is generally high, the grain refinement process driven by USRP is chiefly governed by the dislocation slip mechanism, with instances of deformation twinning through plastic deformation being infrequent. However, the phenomenon of deformation twins in BCC metallic materials stemming from USRP-induced plastic deformation remains unexplored. In the case of hexagonal close-packed (HCP) metallic materials, their reduced crystal symmetry and limited independent slip systems necessitate the orchestration of diverse slip systems and multiple twinning modes to facilitate plastic deformation coordination. While SPD can effectuate grain refinement in coarse-grained metal materials, it is imperative to acknowledge that plastic deformation also has the propensity to incite grain growth, resulting in conspicuous strain-softening tendencies and the attenuation of mechanical properties. This prompts an exploration into the grain growth mechanisms centered on grain boundary migration and grain rotation. Notably, research concerning USRP-induced grain growth in metal materials remains a nascent domain. Further scrutiny unfolds with regard to solute atoms, which may segregate along grain boundaries or dislocation cores. Dynamic interactions with defects such as dislocations, vacancies, and non-equilibrium grain boundaries effectively diminish the driving force and growth rate of grain growth, thereby enhancing the limits of grain refinement through plastic deformation induction. A comprehensive assessment of alloy element-induced grain boundary segregation and dislocation core segregation mechanisms resulting from SPD is also encompassed. Regrettably, the impact of alloy element segregation stemming from USRP-induced plastic deformation on the microstructural evolution and mechanical properties of metal materials remains a considerably under-researched facet. While a substantial body of research on USRP exists both domestically and internationally, its tangible industrial application remains relatively limited. Comparative to foreign counterparts, significant strides have been made in the domain of USRP within our nation. Yet, discernible gaps persist in areas encompassing piezoelectric ceramic base materials, manufacturing processes, drive control technology, and system stability. The culmination of this discourse culminates in a call to action, advocating for the continued research and development of the USRP strengthening process. This pursuit holds the potential to serve as a guiding beacon for the active and precise regulation of surface integrity in metal materials subjected to USRP treatment, thereby ameliorating their operational longevity and dependability. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.