Extension of the 'five-parameter' grain boundary stereological method to textured alloys

晶间降解如腐蚀在许多材料应用中可能是一个严重的问题。因此，研究哪些晶界晶体学参数（即边界结构）比其他参数更能抵抗这种现象是有意义的。最近，它已成为可能使用的体视学技术与电子背散射衍射（EBSD）耦合来测量所有五个晶界晶体学参数，即取向差和边界平面。这一具有里程碑意义的实验进展为晶界结构和性能之间的联系提供了新的见解。然而，目前“五参数分析”还不能应用于具有晶体学织构的材料，包括许多技术上重要的合金。本项目的首要目标是消除这一限制。这将通过设计和实施各种多切片采样程序（即从几个非平行切片平面采集EBSD图）来实现，同时对现有软件代码进行广泛修订，以考虑非随机方向分布，即纹理。然后，新方案将通过应用于Al-Mg-Mn 5xxx系列合金（用于减少汽车底盘应用中的质量）和商业纯钛来验证。将使用聚焦离子束（FIB）显微镜结合EBSD来确认和验证所使用的程序。这些数据将提供关于边界平面分布的信息，这在织构化合金中是迄今为止未知的，并且将允许洞察织构形成的机制。然后，这些信息将被应用于探索Al-Mg-Mn合金中的边界晶体学和晶间腐蚀之间的关系，这将反过来输入到通过适当控制最终规格织构来降低Al-Mg合金对晶间腐蚀的敏感性的更大的主动性。这是一个具有成本效益的项目，因为实验工作非常适合由研究生进行，并且没有设备成本。主要的项目合作伙伴是美国卡内基梅隆大学Rohrer教授的小组，五参数分析是在那里开发的，该小组将进行软件修订。其他项目合作伙伴有：德国海德鲁铝业公司，该公司对铝合金的晶界网络分析感兴趣，并为该项目提供样品;新南威尔士大学，该大学通过补充FIB分析支持该工作。将五参数技术扩展到织构材料将使其作为微观结构工具具有更广泛的适用性。此外，由于EBSD的绘图速度现在非常快，可以设想，在未来的五参数分析可以成为纳入主流晶界分析。

Intergranular degradation such as corrosion can be a serious problem in many materials applications. Hence, it is of interest to study which grain boundary crystallographic parameters (i.e. boundary structure) are more resistant than others to this phenomenon. Recently it has become possible to use a stereological technique coupled with electron backscatter diffraction (EBSD) to measure all five grain boundary crystallographic parameters, i.e. both misorientation and boundary plane. This landmark experimental advance is delivering new insights into the link between grain boundary structure and properties. However, at present the 'five-parameter analysis' cannot be applied to materials which have a crystallographic texture, which includes many technologically important alloys.The first aim of this project is to remove that limitation. This will be achieved by the design and implementation of various multiple sectioning sampling routines (i.e. acquisition of EBSD maps from several non-parallel sectioning planes), in parallel with extensive revision of the existing software code to take into account non-random orientation distributions i.e. texture. Then the new scheme will be validated by application to alloys of the Al-Mg-Mn 5xxx series, which is being used to reduce mass in automotive chassis applications, and to commercially pure Ti. Focused ion beam (FIB) microscopy coupled with EBSD will be used to confirm and validate the procedures used. The data will provide information on the distribution of boundary planes, which is hitherto unknown in textured alloys, and will allow insights into the mechanism of texture formation. This information will then be applied to explore the relationship between boundary crystallography and intergranular corrosion in the Al-Mg-Mn alloys, which will in turn input to the larger initiative of reducing susceptibility of Al-Mg alloys to intergranular corrosion by proper control of the final gauge texture. This is a cost-effective project because the experimental work is well suited to be carried out by a research student and there are no equipment costs. The principal project partner is Professor Rohrer's group at Carnegie Mellon University, USA, where the five-parameter analysis was developed, and who will carry out the software revision. Other project partners are Hydro Aluminium, Germany, who have an interest in grain boundary network analysis in aluminium alloys and are providing specimens for the project, and the University of New South Wales, who are supporting the work with complementary FIB analysis. Extension of the five-parameter technique to textured materials would give it much more general applicability as a microstructural tool. Furthermore, given that mapping speeds by EBSD are now very rapid, it is envisaged that in the future five-parameter analysis could become incorporated into mainstream grain boundary analysis.