Brian M. Gable

Monitoring the evolution of the matrix copper composition in age hardenable Al-Cu alloys

Nuclear magnetic resonance (NMR) was used to systematically monitor the amount of copper in the matrix of various age hardenable Al-Cu alloys as a function of ageing treatment. These NMR results were used to compare the measured amount of copper residing in the matrix during microstructural evolution with that suggested from the equilibrium phase diagrams. Our results indicate that the matrix copper composition for under- and peak-aged microstructures is generally far from equilibrium, with much more copper in solution than expected based on equilibrium phase diagrams. NMR is shown to be a sensitive and efficient metallurgical characterization technique to monitor the partitioning of solute in both non-equilibrium and equilibrium phases.

Early detection of nanoparticle growth from x-ray reciprocal space mapping

The potential for nondestructive in situ detection of the formation of weakly diffracting nanoparticles has been confirmed by a combination of experiment and simulation. A triple axis diffractometer was used to collect two-dimensional reciprocal space maps of diffracted synchrotron x-rays from nanoscale Al2Cu precipitates embedded in a bulk metallic matrix. The appearance and asymmetric profile of the monochromator pseudostreaks are demonstrated to be indicative of the sensitivity of the technique to both the presence and orientation of the nanoparticles. This is a fundamental step toward in situ detection of sparsely dispersed, embedded nanoparticles and to quantitative temporal studies of particle number, scale, and dispersion.

CALPHAD based kinetic Monte Carlo simulation of clustering in binary Al-Cu alloy

A multi-body atomistic model has been developed for precipitation within a FCC substitutional aluminium alloy based upon the CALPHAD thermodynamic databases. Combined with diffusivity data, the model is applied to kinetic Monte Carlo simulation of solute Cu clustering in a binary Al-Cu alloy. Both pairwise and four-body interactions are employed and it is demonstrated that, although limited to next nearest-neighbour distances, the multi-body description results in features that resemble Guinier–Preston (GP) zones. It is not necessary to explicitly introduce long-range elastic interactions to simulate the monatomic planar dimensions, form and crystallography of GP-zones because these effects are inherently captured in the CALPHAD phase descriptions. This result shows that, although long-range interactions are believed to be crucial in the formation of planar features such as GP-zones, first nearest-neighbour multi-body interactions could, in principle, explain their appearance. The model is potentially readily generalised to multi-component alloys.

The Effect of Alloying Additions on Vacancy Behaviour in Aluminium-Copper Alloys

The effect of Si additions on vacancy behavior following solution treatment and quenching was studied for an Al-Cu-Mg-Ag alloy system using positron annihilation lifetime spectroscopy (PALS). Both the initial positron lifetime and steady state positron lifetime increase as the Si concentration increases. This behavior is interpreted in terms of Si interacting with vacancies, leading to their retention in the alloy. The ability of PALS to monitor vacancy behavior after solution treatment should allow the improved prediction of phase transformation kinetics and hence the tailoring of ageing treatments.

Toward in situ x-ray diffraction imaging at the nanometer scale

We present the results of preliminary investigations determining the sensitivity and applicability of a novel x-ray diffraction based nanoscale imaging technique, including simulations and experiments. The ultimate aim of this nascent technique is non-destructive, bulk-material characterization on the nanometer scale, involving three dimensional image reconstructions of embedded nanoparticles and in situ sample characterization. The approach is insensitive to x-ray coherence, making it applicable to synchrotron and laboratory hard x-ray sources, opening the possibility of unprecedented nanometer resolution with the latter. The technique is being developed with a focus on analyzing a technologically important light metal alloy, Al-xCu (where x is 2.0-5.0 %wt). The mono- and polycrystalline samples contain crystallographically oriented, weakly diffracting Al2Cu nanoprecipitates in a sparse, spatially random dispersion within the Al matrix. By employing a triple-axis diffractometer in the non-dispersive setup we collected two-dimensional reciprocal space maps of synchrotron x-rays diffracted from the Al2Cu nanoparticles. The intensity profiles of the diffraction peaks confirmed the sensitivity of the technique to the presence and orientation of the nanoparticles. This is a fundamental step towards in situ observation of such extremely sparse, weakly diffracting nanoprecipitates embedded in light metal alloys at early stages of their growth.

NONDESTRUCTIVE THREE-DIMENSIONAL X-RAY DIFFRACTION IMAGING OF NANOSCALE PARTICLES

We report a novel approach to X-ray diffraction data analysis for nondestructive determination of the shape of nanoscale particles and clusters in three dimensions with a spatial resolution of a few nanometers. The advantage of the proposed approach is that it does not require a coherent X-ray source and therefore is suitable for almost any synchrotron radiation beamline and many laboratory sources. The technique is insensitive to the coherence of the X-rays, and 3D reconstruction of a modal image is possible without tomographic synthesis, rendering the approach suitable for laboratory facilities. Successful application of the technique to the characterization of nanoparticulate in a range of dispersed-phase nanocomposite structures illustrates this novel approach.