Invited Paper AP+AS+SS-TuA3
The Renaissance in Metallurgical Design and the Role of Atom Probe Microscopy

Tuesday, October 29, 2013, 2:40 pm, Room 203 A

The design of materials that demonstrate properties that are ordinarily in conflict with each other is a tantalising frontier of materials science and engineering. The design of metallic (not glassy!) aluminium alloys and new 3^rd generation steels with remarkable combinations of high strength and ductility¹, magnetic carbon with a tuneable bandgap², and materials that exhibit magnetism and superconductivity in the same phase³ represent examples of new metals and materials that exhibit highly sought after properties that are usually in conflict with each other. In these cases, our approach to overcoming these property conflicts is via atomic clustering within the solid solution, and that is the topic of this presentation.

In fact, short-range ordering, atomic clustering, segregation and site-occupancy exert a major influence on the phase transformation pathways, and transformation kinetics in many technologically important supersaturated solid solutions. So, how can these non-periodic structures be described, measured and, ultimately, ‘designed’.

I will discuss a new theory for short-range order^4,5 that provides a framework for describing the atomistic configurations in n-component solid solutions. The characterisation of such materials will then be discussed, in detail. The challenging issues associated with scattering based approaches using X-rays, neutrons or electrons, will be set out and it will be shown that there exist complex convolutions in the diffracted intensity that make the measurement of this 3D atomic architecture extremely challenging.

Finally, I will discuss our approach to addressing these issues using atom probe microscopy. We have recently modelled the origins of resolution in the atom probe, computed advanced spatial distribution maps, which are analogous to Patterson functions in scattering experiments, and used these new tools to devise an approach for ‘lattice rectification’, analogous to aberration correction in TEM. These techniques⁶ are revealing a rich and complex hierarchical architecture of atomic structures within solid solutions, and at microstructural interfaces and these are all discussed in terms of the renaissance in metallurgical design that we in the midst of.

¹ Liddicoat, Liao, Zhao, Zhu, Murashkin, Lavernia, Valiev and Ringer, “Nanostructural hierarchy increases strength of aluminium alloys”, Nature Communications, Vol. 1, Article 63 (2010).

² Cui, Zheng, Liu, Li, Delley, Stampfl and Ringer, “Magic numbers of nanoholes in graphene: tunable magnetism and semiconductivity,” Physical Review B, Vol. 84, Article 125410 (2011).

³ Yeoh, Gault, Cui, Zhu, Moody, Li, Zheng, Li, Wang, Dou, Sun, Lin and Ringer, “Direct observation of local potassium variation and its correlation to electronic inhomogeneity in (Ba_1–xK_x)Fe₂As₂ pnictide”, Physical Review Letters, Vol. 106, Article 247002 (2011).

⁴ Ceguerra, Powles, Petersen, Marceau, Moody and Ringer, Short-range ordering in multicomponent materials, Acta Crystallographica A, (2012, in press)

⁵ Ceguerra, Powles, Moody and Ringer, “Quantitative description of atomic architecture in solid solutions: a generalized theory for multicomponent short-range order”, Physical Review B, Vol. 82, Article 132201 (2010).

⁶, Gault, Moody, Cairney and Ringer, “Atom probe microscopy”, Springer – monograph series in materials science , (2012).