Wu Pan, Song Kexing, Liu Feng
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China.
Henan Academy of Sciences, Zhengzhou 450046, China.
Materials (Basel). 2024 Aug 24;17(17):4197. doi: 10.3390/ma17174197.
So-called strength-ductility trade-off is usually an inevitable scenario in precipitation-strengthened alloys. To address this challenge, high-density coherent nanoprecipitates (CNPs) as a microstructure effectively promote ductility though multiple interactions between CNPs and dislocations (i.e., coherency, order, or Orowan mechanism). Although some strain hardening theories have been reported for individual strengthening, how to increase, artificially and quantitatively, the ductility arising from cooperative strengthening due to the multiple interactions has not been realized. Accordingly, a dislocation-based theoretical framework for strain hardening is constructed in terms of irreversible thermodynamics, where nucleation, gliding, and annihilation arising from dislocations have been integrated, so that the cooperative strengthening can be treated through thermodynamic driving force ∆G and the kinetic energy barrier. Further combined with synchrotron high-energy X-ray diffraction, the current model is verified. Following the modeling, the yield stress σy is proved to be correlated with the modified strengthening mechanism, whereas the necking strain εn is shown to depend on the evolving dislocation density and, essentially, the enhanced activation volume. A criterion of high ∆G-high generalized stability is proposed to guarantee the volume fraction of CNPs improving σy and the radius of CNPs accelerating εn. This strategy of breaking the strength-ductility trade-off phenomena by controlling the cooperative strengthening can be generalized to designing metallic structured materials.
在沉淀强化合金中，所谓的强度-延展性权衡通常是一种不可避免的情况。为应对这一挑战，高密度相干纳米析出相（CNPs）作为一种微观结构，通过CNPs与位错之间的多种相互作用（即相干性、有序性或奥罗万机制）有效地提高了延展性。尽管已经报道了一些关于单一强化的应变硬化理论，但如何人为地、定量地提高由多种相互作用引起的协同强化所产生的延展性尚未实现。因此，基于不可逆热力学构建了一个基于位错的应变硬化理论框架，其中整合了位错的形核、滑移和湮灭，从而可以通过热力学驱动力∆G和动能势垒来处理协同强化。进一步结合同步辐射高能X射线衍射，验证了当前模型。通过建模，屈服应力σy被证明与改进的强化机制相关，而颈缩应变εn则取决于位错密度的演变，本质上取决于增强的激活体积。提出了一个高∆G-高广义稳定性准则，以确保CNPs的体积分数提高σy，CNPs的半径加速εn。这种通过控制协同强化来打破强度-延展性权衡现象的策略可以推广到金属结构材料的设计中。
