Recently, Associate Professor Li Yu's team at SIT, in collaboration with a research team from Shanghai Jiao Tong University, has made significant research progress in the regulation of dislocation structures and the mechanisms of cryogenic strengthening and toughening. The related findings, presented in two papers titled “The controlled incident dislocation boundaries and cell arrangements promoted multi-variant transformation and enhanced strain-hardening in a metastable ferrous medium entropy alloy” and “Influences of dislocation configuration and texture optimization on obtaining exceptional cryogenic strength-ductility synergy in a dynamic-recovered heterogeneous high-manganese steel,” were published consecutively in the top-tier international mechanics journal International Journal of Plasticity (a CAS Q1 TOP journal, IF = 12.8). SIT is the first completion unit for both papers. Postgraduate students Chen Jiehua and Xiong Hao from the Faculty of Materials Technology are the first authors. Faculty members Li Yu, Wang Binjun, and Fu Bin, along with Li Wei from Shanghai Jiao Tong University, served as corresponding authors.
Focusing on the Fe50Mn30Co10Cr10 medium entropy alloy, the team proposed a novel dislocation structure design route: "cold rolling to pre-introduce high-density dislocations → warm rolling to drive dislocation rearrangement into cells." This approach refined the average dislocation cell size from the micron level achieved by traditional single-pass warm rolling to the submicron level and increased the dislocation density by 2.3 times. Consequently, the yield strength was successfully enhanced from 617 MPa to 985 MPa at 77 K while maintaining a uniform elongation exceeding 57%. In-situ EBSD and TEM analyses confirmed that the high-density dislocation cells initially suppress the rapid growth of ε-martensite but later provide nucleation sites for multi-variant nano-lamellar ε-plates, achieving synergistic hardening through "dislocation cell-phase transformation" interaction.
he team further coupled dislocation regulation with texture weakening in high-manganese steel. Through the synergy of dislocation cell refinement and static recrystallization, the intensity of the strong {001}<111> texture was reduced by over 50%, significantly mitigating mechanical anisotropy. Based on this, dislocation cell walls acted as nucleation sites for twinning, inducing high-density 15 nm-scale nano-twins. The dynamic Hall-Petch effect increased the yield strength to 1.35 GPa, while a uniform elongation of 57% was still maintained.
Progressing from "dislocation cell size-density" control to the multi-level synergy of "dislocation-phase transformation-twinning-texture," these two studies establish a systematic methodology for dislocation regulation in cryogenic high-strength and high-toughness metallic materials. This provides material-level solutions for the localization of key components used in extreme environments and underscores SIT's sustained innovation capability in the direction of microscopic mechanisms of metal plasticity and performance regulation.
