Browsing by Author "Ringer, SP"
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- ItemAdditively manufactured Haynes-282 monoliths containing thin wall struts of varying thicknesses(Elsevier, 2022-09-01) Lim, B; Chen, H; Nomoto, K; Chen, Z; Saville, AI; Vogel, SC; Clarke, AJ; Paradowska, AM; Reid, M; Primig, S; Liao, XZ; Babu, SS; Breen, AJ; Ringer, SPMagnitude and distribution of residual stresses in additively manufactured Ni-based superalloys may impact the mechanical performance of as-fabricated parts. Though electron beam powder bed fusion (E-PBF) can produce components with minimal defects and residual stresses compared to laser powder bed fusion and directed energy deposition, variations of them may occur within the complex geometry of a component, due to inherent variations of thermal signatures and the evolution of section modulus along the build direction. This work reveals the residual stress distribution, characterised from neutron diffraction, of an as-fabricated Haynes 282 monolith containing internal cube voids and thin wall struts of varying thicknesses. Complementary local hardness measurements and multi-scale microscopy were used to investigate the geometry-structure-property relationships. Observed variations in hardness were attributed to a combination of type I macro-scale residual stresses and variations in bimodal γ′ precipitation behaviour. The results highlight the influence of residual stresses and microstructure on the mechanical properties of E-PBF Haynes 282. © 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
- ItemElectronic and vibrational properties of yttria-stabilised zirconia from first-principles for 10–40 mol% Y2O3(Elsevier, 2014-11) Cousland, GP; Cui, XY; Ringer, SP; Smith, AE; Stampfl, APJ; Stampfl, CMDensity-functional theory calculations are performed to investigate the electronic and vibrational density-of-states (DOS) for a series of recently predicted stable and metastable structures of yttria-stabilised zirconia (YSZ) with yttria (Y2O3) concentrations of 14, 17 and 20 mol%. Analogous quantities are also studied for the so-called δ-phase, which forms for 40 mol% yttria, as well as for model structures with ≈10.3 mol% yttria. These calculated results, together with those for the cubic, tetragonal and monoclinic phases of ZrO2, afford a comparison of structural, electronic and vibrational properties as a function of yttria concentration. With increasing yttria content, the electronic DOS exhibit a decrease in the valence band-width (of about 2.0 eV relative to the cubic phase) and a corresponding increase of the band-gap of 0.73 eV (from cubic to 40 mol% yttria containing ZrO2). Regarding the vibrational DOS (vDOS), the addition of yttria causes the peaks in the vDOS of ZrO2 to become less distinct, reflecting the more dense occupation of states due to the larger number of atoms in each primitive cell, and to the lower symmetry. The vDOS of the various YSZ structures appear qualitatively similar with contributions from O atoms spanning the whole frequency range and cation related contributions present for frequencies View the MathML source. With increasing yttria content, more Zr atoms become seven-fold coordinated as in monoclinic ZrO2, concominantly the vDOS increasingly resembles that of m-ZrO2, but with notable contributions from Y atoms, which has a main peak at about 17 meV, similar to that of Zr atoms. © 2014 Elsevier Ltd.
- ItemGraphene doping to enhance the flux pinning and supercurrent carrying ability of a magnesium diboride superconductor(Institute of Physics, 2010-08) Xu, X; Dou, SX; Wang, XL; Kim, JH; Stride, JA; Choucair, M; Yeoh, WK; Zheng, RK; Ringer, SPThe effect of graphene doping on the electromagnetic properties of MgB2 has been examined, in comparison with the case for undoped MgB2. It was found that graphene doping is more efficient than other forms of carbon doping for effecting improvement in the critical current density–field performance (Jc(B)), with little change in the transition temperature of MgB2. An optimal enhancement of Jc(B) was achieved for 3.7 at.% graphene doped MgB2, by a factor of 30 at 5 K and 10 T, as compared to undoped MgB2. It is found that spatial fluctuation in Tc is responsible for the flux pinning mechanism of graphene doped MgB2. © 2010, Institute of Physics
- ItemStress/strain induced flux pinning in highly dense MgB2 bulks(Institute of Electrical and Electronics Engineers (IEEE), 2009-06-01) Zeng, R; Dou, SX; Lu, L; Li, WX; Poh, CK; Kim, JH; Horvat, J; Shi, DQ; Wang, JL; Munroe, P; Wang, XF; Zheng, RK; Ringer, SP; Rindfleisch, M; Tomsic, MWe have systematically studied the flux pinning behavior of MgB(2) bulks synthesized by direct diffusion of Mg into pressed pellets of high purity crystalline B powder, with and without mixing with C and SiC nanoparticles, at a reaction temperature of 850 degrees C for 10 hrs. All of the samples showed very high purity and high density, but their microstructure and flux pinning behavior showed significant differences. It was found that the pure MgB(2) agrees with the delta T(c) pinning model, nano-C doped MgB(2) agrees with the delta l pinning model, while the SiC + MgB(2) composite agrees with the delta epsilon pinning model (stress/strain field pinning), since the dominant micro-defects that influence the flux pinning in these three samples are different. © 2009, Institute of Electrical and Electronics Engineers (IEEE)