Pan Qingsong, Ding Kunqing, Guo Song, Lu Ning, Tao Nairong, Zhu Ting, Lu Lei
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, P.R. China.
Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
Science. 2025 Apr 4;388(6742):82-88. doi: 10.1126/science.adt6666. Epub 2025 Apr 3.
Cyclic creep, or ratcheting, is a severe form of fatigue deformation caused by cumulative unidirectional plastic strain under asymmetrical stress cycling with a nonzero mean stress. It often causes premature failure of structural materials, and enhancing ratcheting resistance is a challenge in materials engineering. We demonstrate superior ratcheting resistance in high-strength austenitic stainless steel with a gradient hierarchy of dislocation cells. The ratcheting rate is two to four orders of magnitude lower than for coarse-grained counterparts. Its resistance results from sustained microstructural refinement through deformation-induced coherent martensitic transformations to hexagonal close-packed nanolayers within stable dislocation cells. The progressively refined microstructure mitigates cyclic softening and suppresses strain localization during stress cycling, thus reducing ratcheting strain. The gradient dislocation architecture represents a promising design for high-strength, ratcheting-resistant materials.
循环蠕变，即棘轮效应，是一种严重的疲劳变形形式，由非零平均应力下不对称应力循环作用下的累积单向塑性应变引起。它常常导致结构材料过早失效，而提高抗棘轮性能是材料工程中的一项挑战。我们展示了具有位错胞梯度层次结构的高强度奥氏体不锈钢具有卓越的抗棘轮性能。其棘轮速率比粗晶对应物低两到四个数量级。其抗性源于通过变形诱导的相干马氏体转变，在稳定的位错胞内形成六方密排纳米层，从而实现持续的微观结构细化。逐渐细化的微观结构减轻了循环软化，并抑制了应力循环期间的应变局部化，从而降低了棘轮应变。梯度位错结构是一种有前途的高强度、抗棘轮材料设计。
