超高速激光熔覆铁基涂层固态相变应力松弛与调控机制

Residual stress is the critical factor leading to crack of cladding layer in extreme high-speed laser material deposition, and its effective control is very important to ensure good performance of cladding layer. The stress relaxation effect induced by solid-state phase transition provides inspiration for regulating the residual stress in cladding layer. However, under the complex thermo-mechanical conditions of extreme high-speed laser material deposition, some fundamental issues such as cyclic short-term solid-state phase transition behavior and their stress relaxation mechanism have not been clarified yet. The aim of this proposal is to address the control and adjust of the residual stress in Fe-based coating of CA6NM alloy used in nuclear power. Firstly, in-situ characterization and thermo-mechanical simulation are used to develop a kinetic model for describing the cyclic short-term solid-state phase transitions under high stress/strain and construct a constitutive relationship considering the dependence of phase transition plasticity mechanism on stress level. Secondly, using macro numerical simulation technology, a stress temporal/spatial evolution model is established via the coupling of solid-state phase transitions to clarify the stress relaxation mechanism in solid-state phase transitions. Based on the model, the multifactor coupling technology is explored for regulating the temporal/spatial evolution of solid-state phase transition. Effective regulation on the residual stress in iron-based laser cladding layer is accomplished based on phase transition effect. This study enriches the thermo-mechanical-phase transition fundamental coupling theory that describes the strong nonlinear behavior of metal under intensely varying temperature field and nonuniform constrains. Moreover, it provides a theoretical background and technical support for residual stress regulation in iron-based ultrahigh speed laser cladding layer.

残余应力是导致超高速激光熔覆层开裂的关键诱因，其有效调控是保证熔覆层性能的关键途径。固态相变“诱发”的应力松弛为激光熔覆残余应力调控提供了启示，但超高速激光熔覆过程中短时循环固态相变行为及其应力松弛机制等科学问题尚未澄清。本项目针对核电用CA6NM合金超高速激光熔覆铁基涂层残余应力调控方法展开研究，首先采用原位表征、热力模拟等手段，发展高应力/高应变下循环短时固态相变动力学模型，构建考虑相变塑性机制应力水平依赖的本构关系；其次基于宏观数值模拟技术，建立固态相变耦合下应力时间/空间演变模型，揭示固态相变应力松弛机理；在此基础上，探索基于工艺条件与化学元素的固态相变时间/空间的多因素耦合调控技术，发展基于固态相变效应的铁基熔覆层残余应力调控方法。本项目将夯实金属在剧烈变化温度场和非均匀约束条件下的强非线性“热-力-相变”耦合基础理论，为铁基超高速激光熔覆层残余应力调控提供科学支持。

残余应力是导致超高速激光熔覆层开裂的关键诱因，其有效调控是保证熔覆层性能的关键途径。固态相变“诱发”的应力松弛为激光熔覆残余应力调控提供了启示，本项目围绕这一主题，针对铁基熔覆层，首先采用原位表征、热力模拟等手段，发展高应力/高应变下循环短时固态相变动力学模型，构建了考虑相变塑性机制应力水平依赖的本构关系；其次基于宏观数值模拟技术，建立了固态相变耦合下应力时间/空间演变模型，揭示了固态相变应力松弛机理；在此基础上，发展了基于固态相变效应的铁基熔覆层残余应力调控方法，并进一步开发了多种具有TWIP/TRIP效应的低应力激光增材制造用合金。本项目的研究为激光熔覆及增材制造残余应力调控提供了科学与技术支持。