Browsing by Author "Styles, MJ"
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- ItemAustenite formation kinetics from multicomponent cementite-ferrite aggregates(Elsevier, 2020-09-01) Wu, YX; Wang, LY; Sun, WW; Styles, MJ; Studer, AJ; Bréchet, Y; Arlazarov, A; Hutchinson, CRMetastable austenite strongly influences the mechanical properties of many advanced high strength steels (AHSS) and its formation kinetics during intercritical annealing strongly depend on the initial microstructure. In this contribution, we have performed detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range of Fe-C-Mn and Fe-C-Mn-Si/Al alloys via in situ neutron powder diffraction. Depending on the relative contribution of cementite dissolution in respect to migrating interface of austenite/ferrite, the incomplete dissolution of enveloped cementite limited by slow diffusion in austenite could result in austenite plateauing below equilibrium, while fast dissolution of matrix cementite could result in austenite plateau above equilibrium. Both contributions need to be considered and modelled to describe the austenite formation kinetics. © 2020 Published by Elsevier Ltd on behalf of Acta Materialia Inc.
- ItemAustenite formation kinetics from multicomponent cementite-ferrite aggregates by in situ neutron powder diffraction(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Wu, YX; Wang, LY; Sun, WW; Styles, MJ; Studer, AJ; Bréchet, Y; Hutchinson, CRThe development of third generation advanced high strength steels (AHSS) as the next generation sheet steel grade is driven by the automotive industry. The key processing step is called ‘intercritical annealing’ at temperatures in the region of the ferrite and austenite two-phase field. The transformed austenite during intercritical annealing will be retained at a metastable state in the final microstructure. Controlling the fraction and chemistry of austenite and resulting mechanical properties is critical for many AHSS. The kinetics of austenite formation depend sensitively on the initial microstructure and annealing conditions. In this talk, we will present detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range of AHSS grades via in situ neutron powder diffraction at WOMBAT. The quantitative phase analyses highlight that the saturation of transformation kinetics in relation to global equilibrium is affected by the competition between different interface migration. Depending on the relative contribution of cementite dissolution in respect to migrating interface of austenite/ferrite, the incomplete dissolution of enveloped cementite limited by slow diffusion in austenite could result in austenite plateauing below equilibrium, while fast dissolution of matrix cementite could result in austenite plateau above equilibrium. Both contributions need to be considered and modelled to describe the austenite formation kinetics. The experimental and computational work in this contribution would guide future processing and alloy design of AHSS.
- ItemThe competition between metastable and equilibrium S (Al2CuMg) phase during the decomposition of Al-Cu-Mg alloys(Elsevier, 2015-10-01) Styles, MJ; Marceau, RKW; Bastow, TJ; Brand, HEA; Gibson, MA; Hutchinson, CRThe decomposition sequence of the supersaturated solid solution leading to the formation of the equilibrium S (Al2CuMg) phase in Alsingle bondCusingle bondMg alloys has long been the subject of ambiguity and debate. Recent high-resolution synchrotron powder diffraction experiments have shown that the decomposition sequence does involve a metastable variant of the S phase (denoted S1), which has lattice parameters that are distinctly different to those of the equilibrium S phase (denoted S2). In this paper, the difference between these two phases is resolved using high-resolution synchrotron and neutron powder diffraction and atom probe tomography, and the transformation from S1 to S2 is characterised in detail by in situ synchrotron powder diffraction. The results of these experiments confirm that there are no significant differences between the crystal structures of S1 and S2, however, the powder diffraction and atom probe measurements both indicate that the S1 phase forms with a slight deficiency in Cu. The in situ isothermal aging experiments show that S1 forms rapidly, reaching its maximum concentration in only a few minutes at high temperatures, while complete conversion to the S2 phase can take thousands of hours at low temperature. The kinetics of S phase precipitation have been quantitatively analysed for the first time and it is shown that S1 phase forms with an average activation energy of 75 kJ/mol, which is much lower than the activation energy for Cu and Mg diffusion in an Al matrix (136 kJ/mol and 131 kJ/mol, respectively). The mechanism of the replacement of S1 with the equilibrium S2 phase is discussed. © Crown Copyright 2015 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
- ItemIn situ XRD investigation of the evolution of surface layers on Pb-alloy anodes(Cambridge University Press, 2017-08-22) Clancy, M; Styles, MJ; Beetles, CJ; Birbilis, N; Kimpton, JA; Webster, NASThe electrochemical behaviour of a number of Pb-based anode alloys, under simulated electrowinning conditions, in a 1.6 M H2SO4 electrolyte at 45 °C was studied. Namely, the evolution of PbO2 and PbSO4 surface layers was investigated by quantitative in situ synchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis (QPA). In the context of seeking new anode alloys, this research shows that the industry standard Pb-0.08Ca-1.52Sn (wt%) anode, when exposed to a galvanostatic current and intermittent power interruptions, exhibited poor electrochemical performance relative to select custom Pb-based binary alloys; Pb–0.73Mg, Pb–5.05Ag, Pb–0.07Rh, and Pb–1.4Zn (wt%). The in situ S-XRD measurements and subsequent QPA indicated that this was linked to a lower proportion of β-PbO2, relative to PbSO4, on the Pb-0.08Ca-1.52Sn alloy at all stages of the electrochemical cycling. The best performing alloy, in terms of minimisation of overpotential during normal electrowinning operation and minimising the deleterious effects of repeated power interruptions – both of which are significant factors in energy consumption – was determined to be Pb–0.07Rh. © Cambridge University Press 2022
- ItemModular in-situ reaction chamber design for time resolved diffraction(Oldenbourg Verlag, 2009-09) Styles, MJ; Riley, DP; Christoforidis, J; Olsen, SRIn an effort to mitigate the expense and uncertain performance of customised environment chambers, researchers at the University of Melbourne and the Australian Nuclear Science and Technology Organisation (ANSTO) have designed and are currently constructing a modular reaction chamber, capable of separating the necessities of diffraction methodologies from those of the desired sample environment. The In-Situ Reaction Chamber (ISRC) abstracts many of the details intrinsic to the diffractometer, allowing users to design inexpensive environmental inserts that may be readily customised to their individual needs. Overall, the modularised design aims to reduce the development costs of performing in-situ diffraction experiments, while minimising the experimental setup time and overall uncertainty of ancillary performance. © 2009, Oldenbourg Verlag
- ItemShear stiffness in nanolaminar Ti3SiC2 challenges ab initio calculations(Institute of Physics, 2010-04-28) Kisi, EH; Zhang, JF; Kirstein, O; Riley, DP; Styles, MJ; Paradowska, AMNanolaminates such as the Mn + 1AXn (MAX) phases are a material class with ab initio derived elasticity tensors published for over 250 compounds. We have for the first time experimentally determined the full elasticity tensor of the archetype MAX phase, Ti3SiC2, using polycrystalline samples and in situ neutron diffraction. The experimental elastic constants show extreme shear stiffness, with c44 more than five times greater than expected for an isotropic material. Such shear stiffness is quite rare in hexagonal materials and strongly contradicts the predictions of all published MAX phase elastic constants derived from ab initio calculations. It is concluded that second order properties such as elastic moduli derived from ab initio calculations require careful experimental verification. The diffraction technique used currently provides the only method of verification for the elasticity tensor for the majority of new materials where single crystals are not available. © 2010, Institute of Physics
- ItemSingle crystal elastic constants of the MAX phase Ti3AlC 2 determined by neutron diffraction(Trans Tech Publications, 2010-01-01) Kirstein, O; Zhang, JF; Kisi, EH; Riley, DP; Styles, MJ; Paradowska, AMThe ternary ceramic Ti3AlC2 has an interesting combination of electrical, thermal and mechanical properties. Single crystal elastic constants under the Reuss approximation for the micromechanical state were obtained by analysing the shifts of neutron diffraction peaks while a polycrystalline sample was subjected to a compressive load varying from 5 to 300 MPa. The values of Young’s modulus and Poisson’s ratio computed from the single crystal compliances are in good agreement with those obtained directly from strain gauges and from the average changes in the a and c unit cell parameters.