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Instruments / Technical Area	Publication Details	Published
I12-JEEP: Joint Engineering, Environmental and Processing	The Behaviour of Gum Metal (Ti-36Nb-2Ta-3Zr-0.3O wt.%) During Superelastic Cycling Nicholas Jones , Vassili Vorontsov , David Dye Proceedings of the 13th World Conference on Titanium DOI: 10.1002/9781119296126.ch154 Diamond Proposal Number(s): [6701] Show Abstract ▼ Abstract: Metastable beta titanium alloys, such as Gum Metal (Ti-36Nb-2Ta-3Zr-0.3O wt.%), have received significant attention from the biomedical field over the last decade due to their low elastic modulus. Despite initial skepticism, it is now widely accepted that these alloys undergo a stress-induced transformation when subjected to an applied load, forming an orthorhombic martensite phase within the beta matrix. The reversible nature of this trans formation gives rise to super elasticity, which is of significant interest for engineering applications outside of the biomedical industry. However, little is known as to the stability of the super elastic behaviour with respect to repeated load cycling. Here the response of Gum Metal during super elastic cycling was studied in situ, using high energy synchrotron diffraction. The material was observed to accumulate permanent damage with every cycle and the critical stress required for transformation decreased. The diffraction data was used to track the evolution of the martensite phase, both as a function of applied stress and cycle number. The martensite that formed was highly textured, with two independent orientations observed on each Debye-Scherrerring. These orientations formed at different applied stress es and had different volume fractions at the peak stress. The volume fraction at the peak stress of all martensite orientations increased with cycling, which is believed to increase the defect concentration in the material and hence influence the deformation behaviour.	May 2016
B16-Test Beamline	In situ micropillar deformation of hydrides in Zircaloy-4 Hannah Weekes , Vassili Vorontsov , Igor Dolbnya , J D Plummer , Finn Giuliani , Thomas Britton , David Dye Acta Materialia 92, 81 - 96 DOI: 10.1016/j.actamat.2015.03.037 Diamond Proposal Number(s): [7181, 8179] Show Abstract ▼ Abstract: Deformation of hydrided Zircaloy-4 has been examined using in situ loading of hydrided micropillars in the scanning electron microscope and using synchrotron X-ray Laue microbeam diffraction. Results suggest that both the matrix and hydride can co-deform, with storage of deformation defects observed within the hydrides, which were twinned. Hydrides placed at the plane of maximum shear stress showed deformation within the hydride packet, whilst packets in other pillars arrested the propagation of shear bands. X-ray Laue peak broadening, prior to deformation, was associated with the precipitation of hydrides, and during deformation plastic rotation and broadening of both the matrix and hydride peaks were observed. Post-mortem TEM of the deformed pillars has indicated a greater density of dislocations associated with the precipitated hydride packets, while the observed broad- ening of the hydride electron diffraction spots further suggests that plastic strain gradients were induced in the hydrides by compression.	Jun 2015
I12-JEEP: Joint Engineering, Environmental and Processing	Superelastic load cycling of Gum Metal Vassili Vorontsov , Nicholas Jones , K M Rahman , David Dye Acta Materialia 88, 323 - 333 DOI: 10.1016/j.actamat.2015.01.033 Diamond Proposal Number(s): [6701, 8706] Show Abstract ▼ Abstract: The superelastic beta titanium alloy, Gum Metal, has been found to accumulate plastic strain during tensile load cycling in the superelastic regime. This is evident from the positive drift of the macroscopic stress vs. strain hysteresis curve parallel to the strain axis and the change in its geometry subsequent to every load–unload cycle. In addition, there is a progressive reduction in the hysteresis loop width and in the stress at which the superelastic transition occurs. In situ synchrotron X-ray diffraction has shown that the lattice strain exhibited the same behaviour as that observed in macroscopic measurements and identified further evidence of plastic strain accumulation. The mechanisms responsible for the observed behaviour have been evaluated using transmission electron microscopy, which revealed a range of different defects that formed during load cycling. The formation of these defects is consistent with the classical mathematical theory for the bcc to orthorhombic martensitic transformation. It is the accumulation of these defects over time that alters its superelastic behaviour.	Apr 2015
I12-JEEP: Joint Engineering, Environmental and Processing	Alloying and the micromechanics of Co-Al-W-X quaternary alloys Hui-Yu Yan , James Coakley , Vassili A. Vorontsov , Nicholas G. Jones , David Dye , Howard J. Stone Materials Science And Engineering: A Volume 613, 8 September 2014,, Pages 201208 DOI: 10.1016/j.msea.2014.05.044 Open Access Show Abstract ▼ Abstract: The lattice misfit and diffraction elastic constants in hot rolled polycrystalline Co–7Al–5W–2Ta and Co–6Al–6W–2Ti (at.%) are measured using neutron and synchrotron X-ray diffraction. The misfit in the two alloys was found to be +0.67 and +0.59%, using neutron diffraction at HRPD. The misfit was found to increase with temperature, as in Ni superalloys. This implies that the amount of coherency strengthening increases with temperature. The diffraction elastic constants measured show that the ???? phase is less stiff than the ? matrix in all orientations, which means that load shedding will occur to the ? phase.	May 2014
I12-JEEP: Joint Engineering, Environmental and Processing	Quaternary Alloying Effects and the Prospects for a New Generation of Co-base Superalloys Hui-yu Yan , Vassili Vorontsov , James Coakley , Nicholas Jones , Howard Stone , David Dye Superalloys 2012	Sep 2012

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