Evolution of strengthening phases under in-service stresses and temperatures: phase-field and experimental study

使用应力和温度下强化相的演变：相场和实验研究

• 批准号: 257397553
• 负责人: Dr.-Ing. Reza Darvishi Kamachali
• 金额: --
• 依托单位: Bundesanstalt für Materialforschung und -prüfung (BAM)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/257397553?language=en
• 关键词: Evolution; strengthening; phases; under; service

Precipitation is the most important hardening mechanism in Al alloys. The size and spacing of the precipitates, however, are subject to change during the phase separation. During precipitation, chemical variations in the system largely overlap with internal stresses around the precipitate. Thus, a coupled interaction between the diffusion and mechanical relaxation is expected within the system. In the first period of this project, a strong chemo-mechanical cross-coupling due to composition-dependent elastic constants has been investigated on binary (Al-Li, Al-Cu) and ternary (Al-Cu-Li) alloys and supported by mechanical and microstructural experiments. A paradigm-changing mechanism of inverse ripening and rearrangement of precipitates was uncovered under this chemo-mechanical cross-coupling. Furthermore, theoretical and experimental work on the effect of external load on the microstructure evolution are in progress.In the second period of this project, we will focus on the microstructure evolution under creep conditions. A model for diffusion of vacancies in multicomponent system will be developed. Our studies will focus on the significance of point defects (solute atoms and vacancies). The chemomechanical coupling model will be extended to include the composition-dependent strains (Vegard's law) that will be added to the existing model for composition-dependent elastic constants. We will investigate the redistribution of defects in different stressed environments, i.e. next to (i) precipitates (to understand the effect of vacancies on the inverse ripening), (ii) grain boundaries (to understand the criteria for void nucleation) and (iii) next to the dislocations (to understand the mechanism of climb). The insight gained by these investigations will be combined with the new model of surface/interface diffusion (mentioned-above) to address formation of voids in the later stages of creep.As in the previous project, the simulations will be complemented by experiments on our high purity Al-4Cu-1Li-0.25Mn alloy for validation. Thermomechanical treatments will be applied to vary the vacancy and the dislocation density. The resulting effect on the nucleation and coarsening processes of the precipitates will be studied and quantified by microstructural investigations involving TEM, HRTEM and SAXS measurements. The formation and evolution of voids during creep will be studied by performing creep experiments to different stages of secondary and tertiary creep followed by optical microstructural analysis and micro computer tomography (CT) experiments.

沉淀析出是铝合金最重要的硬化机制。然而，沉淀物的尺寸和间距在相分离期间会发生变化。在沉淀过程中，系统中的化学变化在很大程度上与沉淀物周围的内应力重叠。因此，预计在系统内的扩散和机械松弛之间的耦合相互作用。在本项目的第一阶段，由于成分依赖的弹性常数，强烈的化学-力学交叉耦合已被研究的二元（Al-Li，Al-Cu）和三元（Al-Cu-Li）合金，并通过力学和微观结构实验的支持。在这种化学-机械交叉耦合作用下，发现了沉淀物的逆成熟和重排的范式变化机制。此外，关于外载荷对微观结构演变影响的理论和实验研究也在进行中。在本项目的第二阶段，我们将重点研究蠕变条件下的微观结构演变。建立了多组分体系中空位扩散的模型。我们的研究将集中在点缺陷（溶质原子和空位）的意义。化学力学耦合模型将被扩展到包括组合物依赖的应变（Vegard定律），将被添加到现有的组合物依赖的弹性常数模型。我们将研究不同应力环境中缺陷的再分布，即（i）沉淀物（以了解空位对反向成熟的影响），（ii）晶界（以了解空位成核的标准）和（iii）位错（以了解攀移机制）。通过这些研究获得的见解将与新的表面/界面扩散模型（如上所述）相结合，以解决蠕变后期阶段空洞的形成问题。与之前的项目一样，模拟将通过我们的高纯度Al-4Cu-1 Li-0.25Mn合金的实验进行验证。热机械处理将被应用于改变空位和位错密度。所产生的沉淀物的成核和粗化过程的影响将进行研究和量化的微观结构调查，包括TEM，HRTEM和SAXS测量。蠕变过程中的空洞的形成和演变将通过进行蠕变实验的不同阶段的第二和第三蠕变，其次是光学显微组织分析和微型计算机断层扫描（CT）实验研究。