原子尺度研究Cu-Cr-Zr系合金时效析出行为及合金元素间交互作用机理

Although the microstructure and properties of age-hardened Cu-Cr-Zr system alloys have been investigated and some conclusions on aging behavior of those alloys have been obtained, there are still some ambiguities about precipitation behavior and crystallographic structure of Zr-rich precipitates. Besides, the interaction mechanism between Cr and Zr elements is not clear. Thus, in the study, the tensile strength and electrical conductivity of a series of Cu-Cr-Zr alloy are tested and the interaction mode of Cr and Zr is verified according to function fitting and two-way analysis of variance. The mathematical model of Cr, Zr elements and their interaction effect between properties is also established. The space distribution and existence form of atoms, and mechanism of diffusion of different atoms the precipitation and growth of precipitates are investigated by three dimensional atom probe and high-resolution transmission electron microscopy. The binding energy between solute atoms and vacancies and between the solute atoms are calculated by First-principles Method. The diffusion barrier and path of Corresponding to the solute atoms is also confirmed. The interaction mechanism between Cr and Zr elements is determined on the basis of thermodynamics and kinetics analysis of aging behavior. Moreover, the influence mechanism of Cr element on the precipitation sequence and crystallography of Zr-rich phase is clear. The relation model of composition, microstructure and properties is established, which is beneficial to provide experimental and theoretical basis for alloy optimization and regulation of strengthening and toughening.

Cu-Cr-Zr合金是一种典型的时效强化合金，虽然目前关于合金组织性能的研究较多，对合金时效析出行为的研究也有一些结论。但时效过程中富Zr相的析出行为及其晶体结构的演变规律、Cr与Zr元素间交互作用机理还不清楚。因此，本项目拟通过双因素试验方差分析方法判定合金元素交互作用类型，构建合金元素及其交互作用与性能的数学关系模型；采用三维原子探针、高分辨透射电镜等方法研究时效过程中溶质原子空间分布状态、存在形式及其对各原子的扩散和析出相形核、长大的影响规律；采用第一性原理计算出合金中溶质原子与空位、原子与原子间的结合能，以及相应溶质元素的扩散势垒和路径；从相变热力学和动力学角度分析合金的时效析出行为，揭示Cr、Zr元素间的交互作用机理；探明Cr元素对富Zr相的析出序列及其晶体结构影响机理；建立合金成分-微观组织-合金性能的关联模型，为Cu-Cr-Zr合金成分优化设计和强韧化调控提供试验和理论依据。

Cu-Cr-Zr合金是一种典型的时效强化合金，虽然目前关于合金组织性能的研究较多，对合金时效析出行为的研究也有一些结论。但时效过程中富Zr相的析出行为及其晶体结构的演变规律、Cr与Zr元素间交互作用机理还不清楚。基于以上研究背景，本项目拟通过双因素试验方差分析方法判定合金元素交互作用类型，构建合金元素及其交互作用与性能的数学关系模型；采用三维原子探针、高分辨透射电镜等方法研究时效过程中溶质原子空间分布状态、存在形式及其对各原子的扩散和析出相形核、长大的影响规律，探明Cr元素对富Zr相的析出序列及其晶体结构影响机理，揭示Cr、Zr元素间的交互作用机理。结果表明，在Cu-Cr和Cu-Cr-Zr合金450℃的时效过程中Cr相的析出系列为：过饱和固溶体→G.P区→f.c.c Cr相→有序化→b.c.c Cr相。富Zr相的析出过程为过饱和固溶体→Zr原子团簇→亚稳定CuCrZr相→Cu5Zr相。Cu-Cr和Cu-Cr-Zr合金时效过程中Cr相与基体取向关系的变化过程为：立方-立方(cube-on-cube)关系→Nishiyama-Wasserman (N-W)关系→ Kurdjumov-Sachs (K-S)关系。Cu-Zr合金在450℃时效的析出序列为：过饱和固溶体→Zr的原子团簇→与基体半共格的Cu5Zr相。面心立方结构的Cu5Zr相与基体的取向关系为 。通过沿不同晶带轴对析出相形貌的观察，得出Cu5Zr相的真实形貌为具有一定厚度的圆盘状析出物，且沿基体的{111}Cu面析出。在Cu-Cr-Zr合金中，Zr元素能加速Cr元素的偏聚和促进析出相的析出以及有序化过程，缩短合金到达峰时效的时间，并且能有效的减小PFZ的宽度，抑制Cr相的长大，增加时效后期析出相的稳定性，提高合金的综合性能。在低合金化Cu-Cr-Zr合金中Cr元素能与Cu、Zr元素形成亚稳定CuCrZr相，随后会在时效过程中分解成面心立方结构的Cu5Zr相和体心立方结构的Cr相，延迟Cu5Zr相的形成并抑制其长大。