Browsing by Author "Wexler, D"
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- ItemEffects of heat treatment on microstructure and mechanical properties of wire arc additively manufactured Hastelloy C276 alloy(Materials Australian and The Australian Ceramic Society, 2022-06-01) Qiu, Z; Wu, B; Zhu, H; Wang, ZY; Wexler, D; Van Duin, S; Pan, Z; Li, HHastelloy C276 is a Ni-Cr-Mo based superalloy which has a high potential for application in high temperature and extreme corrosive environment due to its high corrosion resistance and excellent mechanical properties. In this research, the wire arc additive manufacturing (WAAM) process was successfully used to fabricate the defect-free Hastelloy C276 component. The microstructure of the component was characterized using optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction, the mechanical properties were evaluated via tensile and hardness tests. The as-deposited component exhibited anisotropy on both microstructure and mechanical properties. The influences of solid solution heat treatment and stress relief heat treatment on microstructure and mechanical properties were also investigated. It was found that both microstructure and mechanical properties were significantly modified after heat treatment. Preliminary creep tests indicted the texture has a strong influence on the creep performance of the component.
- ItemEffects of post heat treatment on the microstructure and mechanical properties of wire arc additively manufactured Hastelloy C276 alloy(Elsevier, 2021-07) Qiu, ZJ; Wu, BT; Wang, ZY; Wexler, D; Carpenter, K; Zhu, HL; Muránsky, O; Zhang, JR; Li, HJPost-processing is often inevitable for most additively manufactured components in order to improve material properties and product quality. In this study, the influence of post-heat treatments (PHTs) at 871 °C and 1177 °C on the microstructure and mechanical properties of a nickel-base Hastelloy C276 alloy prepared using wire arc additive manufacturing (WAAM) were investigated. The results showed that after a PHT at 871 °C, the as-built alloy was strengthened due to the formation of a large amount of Mo-rich nano-sized μ phase in the interdendritic areas. This was at the expense of a significant ductility loss. In contrast, no μ phase precipitates were observed after PHT at 1177 °C. Furthermore, the 1177 °C treatment led to the dissolution of the Mo-rich p phase which was present in the as-built sample, increased solid-solution strengthening, and improvements in both strength and ductility concurrently. This study enables an improved understanding of post-processing-microstructure-property inter-relationships for Hastelloy C276 alloy prepared by WAAM, providing guidelines for further microstructure optimization through PHT to improve the material's mechanical properties. © 2021 Elsevier Inc.
- ItemEnhanced biocompatibility of PDMS (polydimethylsiloxane) polymer films by ion irradiation(Elsevier B.V., 2012-02-15) Ionescu, M; Winton, BR; Wexler, D; Siegele, R; Deslantes, A; Stelcer, E; Atanacio, AJ; Cohen, DDPDMS films several microns thick deposited on polished Si wafers were irradiated with Mg, Ta, and Fe in the low energy range of 40 keV to 200 keV, and for doses of 1016–1018 ions/cm2. After irradiation the films surface is self-organised into 3D coherent and semi-coherent domains. As a consequence of the surface irradiation conditions and the surface boundary conditions, some domains are highly ordered in the form of parallel waves of approximately 1 μm in height, or the result can be semi-ordered regions or disordered regions. In addition, the surface energy of the irradiated polymer is increasing, as reflected in the decrease in its surface hydrophobicity, which is beneficial for cell adhesion. The irradiated samples were tested in vivo, and the results show an increase in viable cell count of up to 650%. © 2020 Elsevier B.V
- ItemA neutron diffraction investigation of residual stresses in rail ends after severe deformation of rail surfaces(Trans Tech Publications, 2014-07-02) Rathod, C; Wexler, D; Luzin, V; Boyd, P; Dhanasekar, MInsulated rail joints (IRJs) are a primary component of the rail track safety and signalling systems. Rails are supported by two fishplates which are fastened by bolts and nuts and, with the support of sleepers and track ballast, form an integrated assembly. IRJ failure can result from progressive defects, the propagation of which is influenced by residual stresses in the rail. Residual stresses change significantly during service due to the complex deformation and damage effects associated with wheel rolling, sliding and impact. IRJ failures can occur when metal flows over the insulated rail gap (typically 6-8 mm width), breaks the electrically isolated section of track and results in malfunction of the track signalling system. In this investigation, residual stress measurements were obtained from rail-ends which had undergone controlled amounts of surface plastic deformation using a full scale wheel-on-track simulation test rig. Results were compared with those obtained from similar investigations performed on rail ends associated with ex-service IRJs. Residual stresses were measured by neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Measurements with constant gauge volume 3x3x3 mm3 were carried in the central vertical plane on 5mm thick sliced rail samples cut by an electric discharge machine (EDM). Stress evolution at the rail ends was found to exhibit characteristics similar to those of the ex-service rails, with a compressive zone of 5mm deep that is counterbalanced by a tension zone beneath, extending to a depth of around 15mm. However, in contrast to the ex-service rails, the type of stress distribution in the test-rig deformed samples was apparently different due to the localization of load under the particular test conditions. In the latter, in contrast with clear stress evolution, there was no obvious evolution of d0. Since d0 reflects rather long-term accumulation of crystal lattice damage and microstructural changes due to service load, the loading history of the test rig samples has not reached the same level as the ex-service rails. It is concluded that the wheel-on-rail simulation rig provides the potential capability for testing the wheel-rail rolling contact conditions in rails, rail ends and insulated rail joints.
- ItemNeutron residual stress measurements in rails(Taylor & Francis, 2013-07-09) Luzin, V; Prask, HJ; Gnaëpel-Herold, T; Gordon, J; Wexler, D; Rathod, C; Pal, S; Daniel, W; Atrens, ARails were among the first objects of study by neutron diffraction strain measurement and the first experiments were done as early as the late 1980s [1, 2]. This interest is easy to explain: the problem of rail fracturing is critical from the public safety point of view and the penetrating ability of neutrons suggested the possibility of breakthrough experiments and fast progress in this field. It was well-established that residual stresses, both near-surface and interior, played a signifi cant role in the development of defects which led to rail failure. This suggested three distinct approaches of neutron diffraction strain measurement that could contribute to various problems of the rail industry. The first method was to map the complete triaxial stress distribution non-destructively in the interior of an intact rail, ideally before and after significant service. Another approach was to use slices, for example to characterize how different processing methods produce favourable or detrimental stress distributions in rails. A third technique was to make non-destructive measurements, but in critical and not very deep portions of rails, for example, to examine defects and their relation to rail failure in the top running surface of rails, e.g. "white layer" formation. © 2013, Taylor & Francis.
- ItemResidual stresses in rail-ends from the in-service insulated rail joints using neutron diffraction(Trans Tech Pblications, 2013-09-23) Luzin, V; Rathod, C; Wexler, D; Boyd, P; Dhanasekar, MInsulated rail joints (IRJs) are an integral part of the rail track signaling system and pose significant maintenance and replacement costs due to their low and fluctuating service lives. Failure occurs mainly in rail head region, bolt- holes of fishplates and web-holes of the rails. Propagation of cracks is influenced by the evolution of internal residual stresses in rails during rail manufacturing (hot-rolling, roller-straightening, and head-hardening process), and during service, particularly in heavy rail haul freight systems where loads are high. In this investigation, rail head accumulated residual stresses were analysed using neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Two ex-service two head-hardened rail joints damaged under different loading were examined and results were compared with those obtained from an unused rail joint reference sample in order to differentiate the stresses developed during rail manufacturing and stresses accumulated during rail service. Neutron diffraction analyses were carried out on the samples in longitudinal, transverse and vertical directions, and on 5mm thick sliceed samples cut by Electric Discharge Machining (EDM). For the rail joints from the service line, irrespective of loading conditions and in-service times, results revealed similar depth profiles of stress distribution. Evolution of residual stress fields in rails due to service was also accompanied by evidence of larger material flow based on reflected light and scanning electron microscopy studies. Stress evolution in the vicinity of rail ends was characterised by a compressive layer, approximately 5 mm deep, and a tension zone located approximately 5- 15mm below the surfaces. A significant variation of d0 with depth near the top surface was detected and was attributed to decarburization in the top layer induced by cold work. Stress distributions observed in longitudinal slices of the two different deformed rail samples were found to be similar. For the undeformed rail, the stress distributions obtained could be attributed to variations associated with thermo-mechanical history of the rail.© 2014, Trans Tech Publications.
- ItemStructural and morphological modification of PDMS thick film surfaces by ion implantation with the formation of strain-induced buckling domains(Elsevier, 2010-03) Winton, BR; Ionescu, M; Dou, SX; Wexler, D; Alvarez, GAElastomer films with three-dimensional features self-organized into coherent and semi-coherent buckling domains were created by implanting different species of metal ions and combinations thereof, using a metal evaporation ion source, into quality polydimethylsiloxane films. As a result of the implantation process, functionalized discrete regions of strain-induced surface buckling were created, taking the forms of domains of parallel surface waves, semi-ordered regions and disordered regions. In addition, deep, strain-induced, V-shaped cracks were observed to penetrate well into the elastomer matrix. Characterization was via optical microscopy, X-ray diffraction, atomic force microscopy and high-resolution scanning electron microscopy (SEM) in the form of field emission SEM. It was found that controlling the localized strain by altering the metal ion species can control the frequency of the V-shaped cracks and the properties of the buckled areas. These observations and possible mechanisms for the formation of the cracks and domains are discussed in this paper. © 2010, Elsevier Ltd.