Peter V. Liddicoat

Nanostructural hierarchy increases the strength of aluminium alloys

Increasing the strength of metallic alloys while maintaining formability is an interesting challenge for enabling new generations of lightweight structures and technologies. In this paper, we engineer aluminium alloys to contain a hierarchy of nanostructures and possess mechanical properties that expand known performance boundaries-an aerospace-grade 7075 alloy exhibits a yield strength and uniform elongation approaching 1 GPa and 5%, respectively. The nanostructural architecture was observed using novel high-resolution microscopy techniques and comprises a solid solution, free of precipitation, featuring (i) a high density of dislocations, (ii) subnanometre intragranular solute clusters, (iii) two geometries of nanometre-scale intergranular solute structures and (iv) grain sizes tens of nanometres in diameter. Our results demonstrate that this novel architecture offers a design pathway towards a new generation of super-strong materials with new regimes of property-performance space.

New Techniques for the Analysis of Fine-Scaled Clustering Phenomena within Atom Probe Tomography (APT) Data

Nanoscale atomic clusters in atom probe tomographic data are not universally defined but instead are characterized by the clustering algorithm used and the parameter values controlling the algorithmic process. A new core-linkage clustering algorithm is developed, combining fundamental elements of the conventional maximum separation method with density-based analyses. A key improvement to the algorithm is the independence of algorithmic parameters inherently unified in previous techniques, enabling a more accurate analysis to be applied across a wider range of material systems. Further, an objective procedure for the selection of parameters based on approximating the data with a model of complete spatial randomness is developed and applied. The use of higher nearest neighbor distributions is highlighted to give insight into the nature of the clustering phenomena present in a system and to generalize the clustering algorithms used to analyze it. Maximum separation, density-based scanning, and the core linkage algorithm, developed within this study, were separately applied to the investigation of fine solute clustering of solute atoms in an Al-1.9Zn-1.7Mg (at.%) at two distinct states of early phase decomposition and the results of these analyses were evaluated.

Evolution of Nanostructure during the Early Stages of Ageing in Al-Zn-Mg-Cu Alloys

During age-hardening of certain Al-Zn-Mg-Cu alloys, a 90% hardness increase can occur with 75 seconds. The clustering and precipitation of solute element species during this early rapid hardening (RH) period has been investigated through atom probe tomography, transmission electron microscopy, and Vickers hardness measurements. This study has focussed on the effect of copper by analysing three alloys; Al-2.0Zn-1.8Mg-0.7Cu, Al-2.0Zn-1.7Mg-0.2Cu and Al-1.9Zn-1.7Mg (at.%). The early RH reaction in these alloys accounts for up to 70% of the total hardening (peak hardness minus as-quenched hardness) and takes place during the first 60 seconds of ageing. We report preferred solute-solute interactions in the as-quenched materials. This quenched-in nanostructure acts as a template for subsequent solute clustering, the nature of which we have correlated with ageing.

Novel Grain Boundary Solute Architecture in a Nanostructured Ultra-High Strength 7075 Aluminium Alloy

In recent years, the pursuit of higher strength metals and alloys has led researchers to nanometer scale grain refinement. New nanocrystalline engineering techniques have successfully increased properties for a wide range of materials. Here we report a nanocrystalline 7075 alloy processed by high-pressure torsion that exhibits ultra-high strength and features a hierarchical solute architecture. The new hierarchy of solute architecture was discovered through high-resolution characterisation using novel techniques we have developed in atom probe tomography. These new techniques – nanotexture and fine scale solute cluster measurements, are the focus of this paper. Our results indicate that nanometer-scale engineering of solid solutions could offer a pathway towards a new generation of super-strong alloys that hold promise for creating entirely new regimes of property-performance space.

A Tool for Scientific Provenance of Data and Software

For a scientist in the modern era, reliability of results is no longer the key to a successful career in research. Increasingly, scientists must demonstrate the applicability (e.g. usefulness) of their work, as well as ensure the research is accessible (e.g. easy to find and easy to interpret). It is these three traits that define how others perceive a body of scientific work. Analyzing citations, such as h-index, is a mature measure of applicability of publications, but measuring the applicability of software is lagging behind. In this paper, we discuss a potential tool for data and software provenance that can be used to measure data and software applicability through usage reporting and citations.

Atom Probe Tomography at The University of Sydney

The Australian Microscopy & Microanalysis Research Facility (AMMRF) operates a national atom probe laboratory at The University of Sydney. This paper provides a brief review and update of the technique of atom probe tomography (APT), together with a summary of recent research applications at Sydney in the science and technology of materials. We describe recent instrumentation advances such as the use of laser pulsing to effect time-controlled field evaporation, the introduction of wide field of view detectors, where the solid angle for observation is increased by up to a factor of ~20 as well as innovations in specimen preparation. We conclude that these developments have opened APT to a range of new materials that were previously either difficult or impossible to study using this technique because of their poor conductivity or brittleness.