Control of Abnormal Grain Structures in Titanium Forgings

钛锻件异常晶粒组织的控制

• 批准号: 1885694
• 金额: --
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1885694
• 关键词: Control; Abnormal; Grain; Structures; Titanium

Titanium forgings are widely used in airframe applications for highly stressed safety critical components. To obtain high damage tolerance, the alloy Ti-6Al-4V is frequently used in a beta annealed condition which results in a coarse lamella transformation microstructure. This microstructure provides low fatigue crack growth rates owing to the high degree of crack deflection it promotes, which ensures a rough fracture surface and decreases the stress range at the crack tip due to 'closure' effects. However, it has been observed that the beta anneal heat treatment can occasionally lead to a highly inhomogeneous beta grain size, or 'abnormal' grain growth in certain forged products. The origin of this phenomenon is currently poorly understood and will be the subject of this project.The main aims of the PhD project are to understand the mechanisms causing 'abnormal' grain structures to appear in titanium forgings. This will involve the following objectives.1. Characterising the nature of abnormal grains in a range of parts, to build up a picture of the typical conditions that give rise to this problem in industrial production, as well as their typical features, (e.g. grain size, texture and orientation relative to the matrix etc)2. Simulation of the forging conditions to investigate the effect of the relationship to the prior deformed state, texture, and level of break-up, recrystallization of the beta and alpha phases during sub-beta transus forging.3. Simulation of the annealing conditions to investigate their effect on grain growth (e.g. temperature, heating rate). This will be supported with in-situ heating experiments, using direct observation in the SEM.The project is sponsored by Airbus UK.

钛字子在机身应用中广泛用于高度压力安全关键组件。为了获得高损伤耐受性，合金TI-6AL-4V经常在β退火状态下使用，从而导致粗羊皮转化微观结构。由于其促进的高度裂纹挠度，该微观结构提供了低疲劳裂纹的生长速率，从而确保了粗糙的断裂表面并减少了由于“闭合”效应而在裂纹尖端处的应力范围。但是，已经观察到，β退火热处理有时会导致高度不均匀的β晶粒尺寸或某些锻造产物的“异常”谷物生长。目前，这种现象的起源知之甚少，并且将成为该项目的主题。博士项目的主要目的是了解导致“异常”谷物结构出现在钛体中的机制。这将涉及以下目标1。表征异常晶粒在各个部分中的性质，以建立典型条件的图片，这些情况在工业生产中引起了这一问题，以及它们的典型特征（例如，相对于矩阵等，晶粒尺寸，纹理和方向等）2。模拟锻造条件，以研究与先前变形状态，纹理和分裂水平的关系，在subeta transus锻造过程中的β和α相结晶的效果。3。模拟退火条件，以研究其对谷物生长的影响（例如温度，加热速率）。使用SEM中的直接观察，该项目将由AirBus UK赞助，这将由原位加热实验提供支持。