Browsing by Author "Whitfield, RE"

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    Anomalous precursive behaviour for the martensitic material Ni 0.625 Al 0.375
    (Australian Institute of Physics, 2011-02-02) Finlayson, TR; Danilkin, SA; Studer, AJ; Whitfield, RE
    NixAl1-x alloys for 0.615 < x < 0.64 undergo a martensitic transformation upon cooling from a CsCl-type structure to a pseudo-orthorhombic structure [1]. The transformation temperature is extremely composition dependent [2] and for Ni0.625Al0.375 is ~ 80 K [1]. In previous research using an approximate cube of single crystal having x = 0.625 [3], significant strain anisotropy was detected above 80 K. It was suggested that this anomalous strain anisotropy indicated the presence of a martensite precursor within the cubic “parent” phase. The aim of the current research project is to investigate the precursive structural behaviour in the above Ni0.625Al0.375 single crystal using both elastic and inelastic neutron scattering. Results from initial experiments at both the Wombat and Taipan instruments at the Opal Research Reactor will be presented and discussed in relation to previously published strain anisotropy data determined using variable temperature, capacitance dilatometry [3].
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    Field-induced incommensurate spin structure of TbNiAl4
    (American Physical Society, 2012-07-13) Hutchison, WD; Goossens, DJ; Whitfield, RE; Studer, AJ; Nishimura, K; Mizushima, T
    TbNiAl(4) exhibits incommensurate and commensurate magnetic ordering as a function of temperature. As a function of applied field it undergoes a series of magnetic phase transitions. The first of these transitions, into an intermediate spin arrangement, is the source of a large inverse magnetocaloric effect, an unusual result given that an aligning field is being applied. This has potential uses in magnetic cooling. Here, single-crystal neutron diffraction with applied magnetic field is used to obtain the intermediate field spin arrangement in TbNiAl(4). We find that not only does the applied field drive the system from commensurate to incommensurate ordering, but that the phase transition shows hysteresis such that a mixed state simultaneously showing commensurate and incommensurate antiferromagnetic ordering, along with ferromagnetism, can be obtained. © 2012, American Physical Society.
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    In situ synchrotron high-energy x-ray diffraction analysis on phase transformations in Ti-Al alloys processed by equal-channel angular pressing
    (Wiley-Blackwell, 2009-11) Liss, KD; Whitfield, RE; Xu, W; Buslaps, T; Yeoh, LA; Wu, XL; Zhang, DL; Xia, KN
    Mixtures of 47-Al and 53-Ti powders (atomic %) have been consolidated using back pressure equal-channel angular pressing starting with both raw and ball-milled powders. In situ synchrotron high-energy X-ray diffraction studies are presented with continuous Rietveld analysis obtained upon a heating ramp from 300 K to 1075 K performed after the consolidation process. Initial phase distributions contain all intermetallic compounds of this system except Al, with distribution maxima in the outer regions of the concentrations (α-Ti, TiAl3). Upon annealing, the phase evolution and lattice parameter changes owing to chemical segregation, which is in favour for the more equilibrated phases such as γ-TiAl, α(2)-Ti3Al and TiAl2, were followed unprecedentedly in detail. An initial δ-TiH2 content with a phase transition at about 625 K upon heating created an intermediate β-Ti phase which played an important role in the reaction chain and gradually transformed into the final products. © 2009, Wiley-Blackwell.
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    Study of phase formation in metal injection moulding through real time neutron diffraction
    (Insitute of Physics, 2010-12-16) Whitfield, RE; Goossens, DJ; Studer, AJ
    The sintering of metal injection moulded stainless steel was investigated using in situ neutron diffraction with different sintering temperatures, from 1270°C up to 1390°C, with sintering profiles that were based on those used in industry. The production of an unwanted high temperature phase, δ-ferrite, was observed during sintering and is seen to be retained in the final product after sintering. Ferrite production during sintering acts to speed up the sintering process by forming in the grain pores but is unwanted in the final product as it is a soft and malleable phase. The ferrite that was formed at high temperature was observed to not completely disappear during cooling as a result of the coexistence of dual high temperature phases delta-ferrite and gamma-austenite during the high temperature soak. This suggests the segregation of the alloying elements between the two phase which changes the composition of the phase grains and allows the ferrite to exist during cooling, resulting in the unwanted phase in the final product.© 2010, Insitute of Physics
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    Temperature dependence of diffuse scattering in PZN
    (Springer Nature, 2011-08-12) Whitfield, RE; Studer, AJ; Goosens, DJ
    Structural disorder seems to relate to the useful physical properties of ferroelectrics and relaxors. One such material is PZN, PbZn1/3Nb2/3O3. To explore what aspects of the disorder are specific to the polarized state, the temperature dependence of diffuse scattering in PZN has been investigated. The data were collected using both neutron and X-ray single crystal experiments in a range of temperatures from 50 K to 500 K (−223 °C to 227 °C). It has been found that some features, like the diffuse scattering from the B-site ordering, remain unchanged with change of temperature in terms of both intensity and peak shape. However, other diffuse scattering features evolve with T, for example the size effect scattering around the Bragg peaks. The size-effect becomes less pronounced with increasing temperature, with the diffuse scattering becoming more symmetric around the Bragg peaks. The diffuse rods caused by the planar domains change only slightly with temperature. This finding indicates that the planar domains persist into the paraelectric state but that the correlation between lead displacement and the average separation of adjacent lead atoms becomes weaker, suggesting that this size effect may be crucial to the ferroelectric properties. © 2011, The Minerals, Metals & Materials Society and ASM International