Effective Structural Unit Size in Polycrystals: Formation, Quantification and Micromechanical Behaviour

多晶的有效结构单元尺寸：形成、定量和微机械行为

• 批准号: EP/E044514/1
• 负责人: Ian Jones
• 金额: $ 36.63万
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FE044514%2F1
• 关键词: Effective; Structural; Unit; Size; Polycrystals

The concept of grain size playing an important role in the engineering application of polycrystalline metals is well established. During casting and subsequent wrought processing, tried and tested methods are used to refine grain size in order to enhance ductility and increase tensile, yield and fatigue strengths. The advent of electron microscopy based experimental techniques such as electron back scatter diffraction (EBSD) and focussed ion beam (FIB) plus nano-indentation have provided novel, intriguing insights into the deeper aspects of both structural evolution and structure / property relationships. This has included preliminary identification of the critical role of effective structural unit size (rather than grain size) in determining mechanical behaviour. However, understanding of the the relationship between processing and effective structural unit size remains in its infancy for most systems. Consequently, significant progress can now be made in understanding the evolution of structures including recrystallisation processes and variant selection during phase transformation. This offers the potential of refining the structure of a wide range of engineering materials for which phase transformation plays an important role during processing such as steel, titanium, zirconium etc. The fatigue process is very complex but can be simplified conceptually into initiation and crack growth. For high cycle fatigue (HCF) regimes where the number of applied stress cycles can easily exceed 10,000,000 material evaluation relies on specimen or component testing. The majority of the HCF life is spent initiating a defect that then grows rapidly to failure. For materials subject to such HCF regimes, the design principle is to stay below an empirically defined endurance stress so that initiation is prevented. For low cycle fatigue (LCF) the situation is different in that initiation life and growth life can both be used to predict a safe component life. Typically, initiation is again determined empirically by mechanical testing. The current inability to predict fatigue initiation from basic principles stems from the fact that crack initiation is dominated by interactions from grain to grain which are inherently difficult to quantify and to model. Thus, for significant end user applications, the engineer has minimal knowledge defining what aspects of a material, or its processing, influence its performance other than by mechanical testing, which is very time consuming and expensive.Considerable scientific exploration of fatigue has until recently largely failed to assist the material producer and end user in other important ways. In the specific case of the titanium-based alloys, the definition of grain boundaries and subsequent measurement of grain size are notoriously difficult through optical inspection alone. The existence of large colonies of similarly orientated crystallographic units can encourage extensive planar slip structures to develop. In turn, through a process of stress redistribution between relatively weak and strong units , this can have a potentially disastrous effect on component performance. Key issues which determine mechanical properties of interest to the end user include:a) How boundaries behave and what constitutes a boundary for a given load regime.b) Factors in processing and heat treatment that dictate effective structural unit size.c) Modelling capability to provide quantitative predictions of mechanical behaviour including HCF initiation and short crack growth rates.All of these issues form the basis of the current proposal for research.

晶粒尺寸在多晶金属的工程应用中起着重要作用，已经建立了很重要的作用。在铸造和随后的锻炼过程中，使用了经过测试和测试的方法来完善晶粒尺寸，以增强延展性并增加拉伸，产量和疲劳强度。基于电子显微镜的实验技术的出现，例如电子背部散射衍射（EBSD）和聚焦离子束（FIB）加上纳米压缩，为结构进化和结构 /特性关系的更深层方面提供了新颖的，有趣的见解。这包括对有效结构单位大小（而不是晶粒尺寸）在确定机械行为中的关键作用的初步鉴定。但是，在大多数系统中，了解处理与有效的结构单位大小之间的关系仍然处于起步阶段。因此，现在可以取得重大进展，以理解结构的演变，包括重结晶过程和相变期间的变体选择。这提供了完善各种工程材料结构的潜力，这些工程材料在加工过程中起着重要作用，例如钢，钛，锆等。疲劳过程非常复杂，但可以从概念上将其简化为启动和裂纹增长。 。对于高循环疲劳（HCF）方案，所施加的应力周期数量很容易超过10,000,000材料评估依赖于样品或组件测试。大多数HCF寿命都花在了一个缺陷中，然后迅速发展为失败。对于受此类HCF政权的材料，设计原则是保持在经验定义的耐力压力以下，以防止启动。对于低周期疲劳（LCF），情况有所不同，因为启动寿命和生长寿命都可以用于预测安全的成分寿命。通常，再次通过机械测试在经验上确定起始。目前无法从基本原理中预测疲劳启动的目前源于以下事实：裂纹引发是从谷物到谷物之间的相互作用主导的，这些谷物本质上难以量化和建模。因此，对于重要的最终用户应用程序，工程师的知识最少，可以定义材料的哪些方面或处理的其他方面，而不是通过机械测试来影响其性能，这是非常耗时且昂贵的。对疲劳的科学探索始终很大程度上很大程度上很大程度上。未能以其他重要方式为材料生产商和最终用户提供帮助。在钛基合金的具体情况下，仅通过光学检查，晶粒边界的定义和随后的晶粒尺寸的测量很难。类似取向的晶体学单元的大菌落的存在可以鼓励大量的平面滑动结构发展。反过来，通过相对较弱和强部单位之间的应力重新分布的过程，这可能会对组件性能产生灾难性影响。确定最终用户感兴趣的机械特性的关键问题包括：a）边界的行为方式和什么构成给定负载状态的边界。B）处理和热处理的因素决定有效的结构单位大小。C提供对机械行为的定量预测，包括HCF启动和短裂纹增长率。这些问题的所有问题构成了当前研究建议的基础。

项目成果

Microstructure and mechanical property of directionally solidified Ti-46Al-0.5W-0.5Si alloys with and without Gd

• DOI: 10.1016/j.intermet.2011.08.008
• 发表时间: 2012
• 期刊: Intermetallics
• 影响因子: 4.4
• 作者: R. Ding;I. Jones;Y. Chiu;Ruirun Chen

A study of dislocation transmission through a grain boundary in hcp Ti-6Al using micro-cantilevers

• DOI: 10.1016/j.actamat.2015.10.023
• 发表时间: 2016-01-15
• 期刊: ACTA MATERIALIA
• 影响因子: 9.4
• 作者: Ding, Rengen;Gong, Jicheng;Jones, Ian P.
• 通讯作者: Jones, Ian P.

TEM of deformed Ti-6Al-4V micro-cantilevers

变形 Ti-6Al-4V 微悬臂梁的 TEM

• 发表时间: 2011
• 作者: Rengen Ding

Preparation of an oriented FIBbed Ti-6Al-4V sample for in situ TEM observations of dislocation transmission through alpha/beta interfaces

制备定向 FIBbed Ti-6Al-4V 样品，用于通过 α/β 界面进行位错传输的原位 TEM 观察

• 发表时间: 2011
• 作者: Joel Douin

Application of a novel EBSD-FIB method to the transmission of c + a dislocations through / interfaces Ti-6Al-4V for producing in situ tension transmission electron microscopy specimens

应用新型 EBSD-FIB 方法通过 Ti-6Al-4V 界面传输 c a 位错，以生产原位张力透射电子显微镜样品

• DOI: 10.1093/jmicro/dfr077
• 发表时间: 2011
• 期刊: Journal of Electron Microscopy
• 作者: Ding R