Browsing by Author "Wang, G"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    The characterisation and formation of novel microstructural features in a Ti−Nb−Zr−Mo−Sn alloy manufactured by Laser Engineered Net Shaping (LENS)
    (Elsevier, 2021-01) Zhu, HL; Wang, ZY; Muránsky, O; Davis, J; Yu, S; Kent, D; Wang, G; Dargusch, MS
    Novel microstructural features were found in the Ti−Nb−Zr−Mo−Sn alloy manufactured by Laser Engineered Net Shaping (LENS). Examination of the microstructure showed that the fabricated sample exhibits a layered morphology with arced deposit boundaries. Novel distributions and morphologies of various phases including β, α, α'' and ω were detected in the LENS-manufactured part which substantially differ to conventionally processed alloy counterparts. The β grains and subgrains spread over multiple deposits and layers, aligned to the build direction, forming a complex network microstructure comprising large highly textured columnar grains aligned to β phase <001> orientations. The α precipitates have needle-like shapes and are widely distributed across a majority of the deposited layers, whereas the nanoscale ω particles were present in regions absent of α precipitation. Localised, massively transformed α'' phase with a very long and curved rod-like shape and substantial surface defects was identified. The formation of these novel microstructural features is investigated and discussed in the context of the characteristics of the LENS fabrication process. The microstructures are attributed to the complex thermal history in the unique deposit-by-deposit and layer-by-layer method employed during LENS additive manufacturing in conjunction with the complex precipitation behaviours exhibited by TiNb-based alloys. The characteristics and formation mechanisms of the LENS-manufactured Ti−Nb−Zr−Mo−Sn alloy microstructures revealed here provide a basis to optimize LENS and post-LENS heat treatment processes to optimize microstructures for improved performance. © 2020 Elsevier B.V
  • No Thumbnail Available
    Item
    Collective nonlinear electric polarization via defect-driven local symmetry breaking
    (Royal Society of Chemistry, 2019-05-17) Dong, W; Cortie, DL; Lu, T; Sun, QB; Narayanan, N; Hu, WB; Jacob, L; Li, Q; Yu, DH; Chen, H; Chen, AP; Wei, XY; Wang, G; Humphrey, MG; Frankcombe, TJ; Liu, Y
    In this work, we report the defect-mediated, abnormal non-linear polarization behavior observed in centrosymmetric rutile TiO2 where less than 1 at% of sterically mismatched Mg2+ ions are introduced to create ferroelectric-like polarization hysteresis loops. It is found that the Image ID:c9mh00516a-t2.gif defect cluster produces a dipole moment exceeding 6 Debye, with a rotatable component. Such a polarization is further enhanced by the displacement of neighboring Ti4+ ions. The coupling between such defect-driven symmetry-breaking regions generates a collective nonlinear electrical polarization state that persists to high temperatures. More importantly, an observation of abnormal bias shift of polarization hysteresis suggests an antiparallel alignment of certain dipoles frozen relative to the external poling electric field, which is associated with oxygen vacancy hopping. This result challenges the long-standing notion of parallel alignment of dipoles with the external electric field in ferroelectrics. This work also reveals an unexpected new form of non-linear dielectric polarization (non-ferroelectricity) in solid-state materials. © Royal Society of Chemistry 2024
  • Thumbnail Image
    Item
    Lead-free (Ag,K)NbO3materials for high-performance explosive energy conversion
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Liu, Z; Lu, T; Xue, F; Withers, RL; Studer, AJ; Narayanan, N; Dong, XL; Yu, DH; Chen, L; Wang, G; Liu, Y
    Explosive energy conversion materials with extremely rapid response times have a diverse and growing range of applications in energy, medical, and mining areas. Research into the underlying mechanisms and the search for new candidate materials is so limited that Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 is still the dominant material after half a century. In this work, we report the discovery of a new, lead-free ferroelectric material, (Ag0.935K0.065)NbO3 for explosive energy conversion applications. This material not only possesses a record-high energy storage density of 5.401 J/g, but also exhibits excellent temperature stability (up to a disruptive ferroelectric to ferroelectric phase transition at 150oC) by comparison with Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (which exhibits the ferroelectric to ferroelectric phase transition but at the much lower temperature of 41~70oC). (Ag0.935K0.065)NbO3 enables extremely high power, energy conversion within 1.8 microseconds, generating a pulse with e.g. a current ~ 22 A. Furthermore, pressure-dependent physical characterization, together with transmission electron microscopy, in-situ neutron diffraction analysis and theoretical modelling, reveals the mechanism underlying the observed explosive energy conversion behavior. It is found that the fast release of the stored energy can be attributed to a pressure-induced octahedral tilt change from a-a-c+ to AgNbO3-type a-a-c-/a-a-c+, in accordance with an irreversible pressure driven FE-AFE phase transition. This work provides not only an alternative (with significantly better performance) to the current commercially-employed lead-containing materials, but also provides guidance for the further development of new materials and devices for explosive energy conversion applications. Copyright © 2020 The Authors.
  • Thumbnail Image
    Item
    Negative thermal expansion of Ni-doped MnCoGe around room temperature - magnetic tuning
    (Australian Institute of Physics, 2019-02-05) Ren, QY; Hutchinson, WD; Wang, JL; Studer, AJ; Wang, G; Zhou, H; Ma, J; Campbell, SJ
    Several materials have been shown to exhibit abnormal contraction with increasing temperature; the phenomenon of negative thermal expansion (NTE). Given this special property, NTE materials fulfill important functions in many modern technologies, such as electrodes of fuel cell, organic light-emitting diode (OLED), optical fibre, as well as high precision electronics and optical mirrors. In general, Nate properties are associated with local structural distortions or phase transitions, such as transverse phonon vibration in rigid unit modes, exile network of metal-organic framework, charge transfer, magneto-volume effect, ferroelectric transition, as well as displacive phase transition. Control or manipulation of Nate properties have become topics of increasing importance over the past two decades. Effective methods to produce materials with Nate properties include chemical doping, nanostructuralization, hydration and applied pressure. Recently, MoCoGe-based compounds were considered as a group of materials that exhibit giant NTE, with this behaviour attributed to the displacive martensitic phase transformation. In this investigation, we reported a new method to manipulate the NTE properties using applied magnetic fields. It is found that doping of 5% Ni on the Mn site could bring about a magneto-structural (MS) coupling in MnCoGe-based compounds. Magnetic-field-dependent neutron diffraction measurements demonstrated that an 8 T magnetic field could suppress the NTE by 31% at 295 K through this MS coupling.