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Browne, David J.
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Browne, David J.
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Browne, David J.
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Now showing 1 - 10 of 34
- PublicationResearch-informed Education in Materials Science and Engineering: a Case Study(The International Council on Materials Education, 2016)
; ; ; A course in Metals Processing, delivered to senior engineering students, in which much of the curriculum consists of summaries of selected relevant research projects, is presented. A balanced research team, under the leadership of the course co-ordinator, has designed and delivered an advanced module covering the near net shape processing of metallic alloys. The topics covered include alloy solidification and casting, plasticity and metal forming, and a practical laboratory exercise. Details of the course content, and the research on which much of it is based, are hereby presented, along with commentary on the pedagogic rationale for the approach taken.317 - PublicationDirect observation of spatially isothermal equiaxed solidification of an Al-Cu alloy in microgravity on board the MASER 13 sounding rocketFor the first time, isothermal equiaxed solidification of a metallic alloy has been observed in situ in space, providing unique benchmark experimental data. The experiment was completed on board the MASER 13 sounding rocket, launched in December 2015, using a newly developed isothermal solidification furnace. A grain-refined Al–20 wt%Cu sample was fully melted and solidified during 360 s of microgravity and the solidification sequence was recorded using time-resolved X-radiography. Equiaxed nucleation, dendritic growth, solutal impingement, and eutectic transformation were thus observed in a gravity-free environment. Equiaxed nucleation was promoted through application of a controlled cooling rate of −0.05 K/s producing a 1D grain density of ~6.5 mm−1, uniformly distributed throughout the field of view (FOV). Primary growth slowed to a visually imperceptible level at an estimated undercooling of 7 K, after which the cooling rate was increased to −1.0 K/s for the remainder of solidification and eutectic transformation, ensuring the sample was fully solidified inside the microgravity time window. The eutectic transformation commenced at the centre of the FOV proceeding radially outwards covering the entire FOV in ~3 s. Microgravity-based solidification is compared to an identical pre-flight ground-based experiment using the same sample and experiment timeline. The ground experiment was designed to minimise gravity effects, by choice of a horizontal orientation for the sample, so that any differences would be subtle. The first equiaxed nucleation occurred at an apparent undercooling of 0.6 K less than the equivalent event during microgravity. During primary equiaxed solidification, as expected, no buoyant grain motion was observed during microgravity, compared to modest grain rotation and reorientation observed during terrestrial-based solidification. However, when the cooling rate was increased from −0.05 K/s to −1.0 K/s during the latter stages of solidification, in both 1g and micro-g environments, some grain movement was apparent due to liquid feeding and mechanical impingement of neighbouring grains.
379Scopus© Citations 32 - PublicationValidation of a Front-Tracking Model of the Columnar to Equiaxed Transition using Solidification Results from the Maxus 7 Microgravity Platform(The Japan Society of Microgravity Application, 2008-03)
; ; ; ; To study the columnar-to-equiaxed transition (CET) in alloy castings, three aluminum-silicon samples were solidified onboard the MAXUS 7 sounding rocket. Temperature measurements were made during the flight and the samples were retrieved and analyzed for their solidified macrostructure. Two of the samples produced a CET while the third sample produced a mixed structure with grains nucleating on the crucible walls. A novel front tracking model of solidification and a model of the MACE test apparatus are presented. Validation of the solidification code is carried out. Cooling curves from the experiments are predicted. A simulation of the solidified macrostructure is also given for each experiment. The CET positions are predicted in agreement with the experimental results.73 - PublicationMeso-scale thermal and solidification modelling for metallic additive manufacturing processes(Faculty of Civil Engineering, 2021-06)
; ; ; ; ; ; The emergence of additive manufacturing (AM) in recent decades signifies a paradigm shift in how we think about manufacturing. Throughout history, breakthroughs in manufacturing were focused on mass production, with a “one size fits all” mentality. Whilst for large batch size applications this has invariably decreased unit manufacturing costs, increased throughput and decreased prices for customers, it also imposes significant limitations for small batch production. Conventional manufacturing requires many highly specialised steps and equipment, requiring significant resources to establish and setting the barrier to entry unfeasibly high for fledgeling SMEs to enter the manufacturing space. Coupled with this, it inevitably forces manufacturers to be unresponsive to their customers’ needs, as changes to a product or manufacturing process are costly, and require significant machine downtime. Additive manufacturing on the other hand offers virtually limitless freedom to the manufacturer to make changes to a product, even for a one-off bespoke application, without significant machine downtime or costly modification to the manufacturing process. Perhaps even more importantly, since parts are generated additively many of the restrictions that traditional machining imposes on part design no longer apply, allowing for near-net- shape, highly optimised structures to be realised. However, these advantages do not come without a cost. Widespread adoption of AM is still hampered by less than ideal mechanical performance.94 - PublicationCharacterization of Micro Injection Molding Process for the Replication of Micro/Nano Features Using Bulk Metallic Glass InsertMicrosytems are motivating the development of complex, net-shape products weighing a few milligrams or having micro/nano features. Such small components or micro/nano features are subject to extreme shear rates and thermal gradients in the micro injection molding process due to their large surface to volume ratio. Detailed process monitoring and characterization are desirable to create a viable manufacturing process with acceptable part quality for MEMS and Microsystems. This work covers the replication of micro/nano scale features using Bulk Metallic Glass (BMG), implementation of a suite of PT (pressure and temperature) sensors on a commercial reciprocating micro injection molding machine, and detailed analysis of the relationship between process-rheology-replication. The results indicate that injection velocity dominates the average viscosity of polymer melts; holding pressure can adjust the input pressure history for micro/nano features and mold temperature can enhance feature filling by elevating the po-mold interface temperature. Tailored strategies to set machine parameters for different molds and plastics can be developed to meet the quality requirement for both small components and micro/nano features.
645 - PublicationXRMON-SOL microgravity experiment module on Maser-13(ESA, 2017-06-15)
; ; ; ; ; The XRMON-SOL microgravity experiment observed spatially isothermal equiaxed solidification of an Al–Cu alloy in microgravity on board the MASER 13 sounding rocket, launched in December 2015. It is the first time that isothermal equiaxed solidification of a metallic alloy has been observed in situ in space, providing unique benchmark experimental data. The experiment used a newly developed isothermal solidification furnace in the re-used module of the MASER 12 experiment XRMON-GF. A grain-refined Al–20 wt%Cu sample was fully melted and solidified during 360 s of microgravity and the solidification sequence was recorded using time-resolved X- radiography. Equiaxed nucleation, dendritic growth, solutal impingement, and eutectic transformation were thus observed in a gravity-free environment. This paper describes the technology development of the experiment module.134 - PublicationTwin roll casting of bulk amorphous alloys: modelling and experimental validationThere is a growing commercial need for semi-finished flat bulk metallic glass product (BMG), in sheet or strip form, for further shaping into components or containers by forming when in the supercooled liquid state. It has been shown tha ttwin roll casting is a viable method to continuously produce flat amorphouse allow strip of a few mm in thickness. However the process has to be carefully designed and controlled to ensure successful production of a fully amorphous product. To assist with the design of experiments, a steady state model of twin roll casting of BMGs has been developed and used to simulate the continuous casting a Mg65Cu25Y10 alloy. The alloy's thermophysical properties were measured to ensure reliable modelling. Twin roll casting experiments were carried out to assess the validity of the model simulations. The model predicted that it would be possible to roll cast the alloy to a thicness of 1.5 mm at speeds of up to 7cm/s using Cu-Be rolls of 190 mm diameter. This was found to be in good agreement with the outcome of the twin roll casting trials which successfully produced fully amorphous strip at these parameter settings.
77 - PublicationComparison of nucleation and growth mechanisms in alloy solidification to those in metallic glass crystallisation - relevance to modelingThe development of microstructure during phase transformations is often best understood by considerations of nucleation in the parent material followed by growth of the new phase. This is a mature research field in alloy solidification, thanks to extensive investigations of nucleation and dendritic growth in cooling alloy melts. Bulk metallic glasses, on the other hand, typically do not form crystals on cooling from above the liquidus to below the glass transition temperature, resulting in very strong hard materials. As BMG toughness can be enhanced by a crystallising anneal, the study of nucleation and growth of crystals in viscous multi-component liquids has become an important topic for study. Such devitrification can lead to crystalline-glass composites or bulk nano-crystalline alloys, and the micro- or nano-structure is controlled by phenomena such as diffusion of solute and heat, and impingement dynamics. The relevance of solidification theories of nucleation, growth and impingement to crystallisation in amorphous alloys is discussed in this paper. The effects of the key differences between phase transformations in alloy casting processes and those in alloy devitrification on development of computational models for process simulation are highlighted.
755Scopus© Citations 4 - PublicationNon-steady 3D dendrite tip growth under diffusive and weakly convective conditions(Elsevier, 2019-03)
; ; ; ; ; Three dimensional α-Al dendrite tip growth under varying solute gradients in an Al-Cu-Si alloy melt has been studied using real time synchrotron X-ray imaging and mathematical modelling. X-radiographic image sequences with high temporal and spatial resolution were processed and analysed to retrieve three-dimensional spatial details of the evolving dendrite and the solute concentration field, providing vastly improved estimates for the latter, in particular for the melt regions adjacent to the dendrite tips. Computational results obtained from an extended Horvay-Cahn dendrite tip model, capable of taking into account the effects of sample confinement, showed good agreement with the experimental data, and can be taken to verify the robustness of the 3D data extraction protocol.329Scopus© Citations 10 - PublicationEffect of design on the replication of micro/nano scale features by micro injection mouldingThe replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High density polyethylene (HDPE) was used as the moulding material. The influence of feature configuration, length, width, gap distance between features, location on substrate, and substrate thickness on the quality of replication was investigated. The experiments revealed that the replication of ridges, including feature edge, profile and filling distance, was sensitive to the flow direction; a critical feature length was found below which the filling of features was significantly reduced. Both the feature location and the substrate thickness had an influence on the filling of micro/nano features while the gap distance had a negligible effect on the replication of features.
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