1,427 research outputs found
Nanostructures in austenitic steel after EDM and pulsed electron beam irradiation
No full textThe resulting recast layer from EDM often exhibits high levels of residual stress, unacceptable crack density and high surface roughness; all of which will contribute to diminished surface integrity and reduced fatigue life. Previous studies have shown that the surface of EDM'd components can be successfully enhanced through the use of large-area pulsed electron beam surface modification, which, through a rapid remelting process, results in a net smoothing of the workpiece surface. It has also been shown that cracks created by EDM are repaired within the region molten by EB irradiation, and therefore the process is proposed to reduce the impact of EDM on fatigue life and deleterious surface properties. In this work the complex multilayers of the near surface are interrogated by TEM and XRD. A FIB-TEM study of the entire remelted layer produced by the irradiation process has been performed for the first time. The characterisation of these layers is necessary for predicting the performance of the material in application. Pulsed EB irradiation was shown to be capable of creating several distinct surface layers of nanostructures which consist of varying grain sizes and grain orientations. Austenite was revealed as the dominant phase in the remelted layer, with a grain size as small as 5 nm produced at the very top surface. A needle-like phase also present in the layer is thought to be cementite
The effect of large-area pulsed electron beam melting on the corrosion and microstructure of a Ti6Al4V alloy
No full textThe use of titanium alloys in biomedical applications continues to increase due to the excellent stiffness to weight ratio and high corrosion resistance. In order to improve the surface wettability and corrosion properties of a Ti-6Al-4V alloy, the surface treatment method, large area electron beam melting technique was investigated. Polished samples were subject to pulsed treatments of 1, 15 and 25 at 1.38 J/cm2 beam energy. Surface roughness and contact wetting angles were reduced as a result of the treatment. Microstructural analysis of the surface by XRD and FIB-TEM revealed a martensitic alpha prime phase formed as a result of the high cooling rates induced by the treatment. The presence of this homogenous martensite layer was shown to facilitate a compact passive oxide layer formation during corrosion, thus improving corrosion rates by several orders of magnitude compared to an untreated sample. Large area electron beam melting of Ti-6Al-4V induced a number of changes to the near surface microstructure of the samples, all of which could be used to tailor mechanical and corrosion properties to that of a desired application, without compromising the bulk material properties. These are explored in detail in this work
Dry sliding friction and wear behaviour of an electron beam melted hypereutectic Al–Si alloy
No full textThe economic and environmental benefits of using light-weighting technology in automotive applications continue to attract attention for feasible commercial solutions. This study investigates the use of pulsed electron beam melting of a hypereutectic Al–Si alloy as a possible modification procedure for cylinder crankcase bore facing surfaces. Machined surfaces of an A390 alloy were subjected to five pulsed electron doses with an applied cathode potential between 16.5 and 36 kV. It was found that increasing beam accelerating voltages led to an initial decrease (1.4 ?m R a) but subsequent increase (4.0 ?m R a) in average surface roughness values associated with surface crater formation due to sub-surface melting and eruption. Surfaces were tested under dry sliding tribological conditions against 52100 bearing steel in a reciprocating geometry. Average dynamic friction coefficients were higher (0.9) compared to the untreated alloy surface (0.6) as a result of a greater degree of adhesion to the counterface. However, FIB cross sections of worn surfaces indicated that this activated an oxidative type wear process which ultimately led to the formation of a beneficial surface tribo-film on the EBM-treated surfaces, improving the specific wear rates by up to 66%
Pulsed electron beam surface melting of CoCrMo alloy for biomedical applications
No full textThe use of CoCrMo alloys in biomedical applications has come under scrutiny recently due to unacceptable revision rates of certain hip resurfacing and total hip arthroplasty designs. Failure analysis has demonstrated that solid and soluble wear debris and corrosion products, released from the joints have resulted in adverse local tissue reactions (ALTR), pseudo-tumour formation and ultimately implant retrieval and replacement. In order to improve the surface properties of a wrought CoCrMo alloy, a low energy high current pulsed electron beam surface treatment process was investigated. Samples were irradiated at two cathode voltages of 15 and 35 kV at pulse numbers of 1, 15 and 25. At low beam energies a polishing effect was observed as a result of surface melting. At higher beam energies a higher Ra value was the result of the formation of surface craters. Nano-indentation and scratch testing of the treated surface were carried out using a nano-indenter. Depth profiling nano-indentation was performed using a Berkovich tip in load control. Loading was performed in 8 mN increments up to 160 mN at a rate of 3.5 mN/s, with a 60 s dwell period and 40% unloading. The results demonstrated that the surface treatment process reduced both the modulus and the hardness of the surface in comparison to the control. Scratching was performed with a 20 ?m radius spherical diamond and loading rate of 2 mN/s up to a maximum of 100 mN, over a 1 mm scratch length. Similar scratch depths for both control and treated surfaces were observed. However, an improvement in the dynamic friction coefficient was observed at certain beam energies. These results are discussed in the light of XRD evidence that suggested rapid cooling of the surface induced preferential formation of an ?-martensite HCP phase which may be beneficial for biomedical applications.<br/
Corrosion resistance enhancement of Ti-6Al-4V Alloy by pulsed electron irradiation for biomedical applications
No full textMetallic materials are commonly used in biomedical applications, especially with the increased use of artificial hip and knee joints in recent years. Ti-6Al-4V alloy is a widely used biomaterial for orthopaedic and dentistry applications, due to its excellent mechanical properties and corrosion resistance. However, the in-vivo environment in which it operates is aggressive in terms of mechanical loading cycles and corrosive activity of bodily fluids. Therefore, metal ions may be released from these alloys due to corrosion and wear, which may cause adverse long-term health effects. Preserving the integrity of component surfaces made from these alloys is critical to ensuring they perform correctly over the required life-cycle and do not generate excessive levels of ion release or wear particles. In this work a large-area pulsed electron beam irradiation technique was investigated to improve corrosion performance of an orthopaedic Ti-6Al-4V alloy. The alloy samples had a lapped surface finish prior to electron beam irradiation using a Sodick PF-32A EBM machine. The process uses an argon plasma as a source of electrons which are accelerated towards and bombard the sample surface, causing surface melting and extremely rapid solidification rates of up to 109 K s-1. For this study, samples were irradiated using a range of acceleration voltages (15-35kV) and numbers of pulses (1-25). The corrosion behaviour of the alloy treated with different acceleration voltages and pulses was investigated by electrochemical techniques including open-circuit potential measurements, polarization tests and electrochemical impedance spectroscopy in a 3.5 wt.% NaCl solution. The corrosion resistance of the titanium alloy treated by e-beam surface melting was enhanced by two orders of magnitude compared to the untreated sample. The enhancement was evaluated by assessing surface topography and microstructure from the treatment as observed by XRD, SEM and TEM characterization
Architecture of fluvio-deltaic sandbodies: the Namurian of Co. Clare, Ireland, as an analogue for the Plio-Pleistocene of the Nile Delta
No full textUnderstanding and predicting the size, shape and internal architecture of sandbodies is of fundamental importance in hydrocarbon exploration. High quality hydrocarbon reservoirs are often formed in deltaic environments where there is a complex interplay between changes in relative sea level, sediment input and climate. When combined with the intrinsic sedimentary variability of deltas, this makes prediction of the internal facies distributions and architectures of deltaic sandbodies a challenging task. The aim of this thesis is to conduct a detailed qualitative and quantitative field study of fluvial and deltaic sandbody architecture and facies distribution, and to assess the usefulness of the data thus obtained in predicting the
architecture and sedimentary characteristics of reservoir sandstones in the subsurface.
The El Wastani Formation of the Nile Delta, Egypt, has previously been identified as an interval of reservoir quality sandstones within the Plio-Pleistocene deltaic succession. Limited core data, and poor seismic imaging due to gas seepage effects, hindered past attempts to assess the internal architecture and facies of the sandbodies. Therefore it was considered appropriate to use an outcrop analogue to aid understanding of the El Wastani Formation reservoir characteristics. From a review of literature, the Upper Carboniferous fluvial and deltaic sandstones of the Central Clare Group, County Clare, western Ireland,
were found to be suitable analogues for the El Wastani Formation sandstones. Controls on the two sedimentary systems were similar; both were fluvial-dominated and wave-influenced, and both show evidence for fluctuating relative sea-level. Comparisons of facies observed in outcrop (Co. Clare) and interpreted from image logs (Nile Delta) show similar facies and sedimentary successions in the two systems, improving confidence in the choice of analogue.
Fieldwork carried out on the Upper Carboniferous (Namurian) coastal outcrops of Co. Clare produced detailed measurements of facies distributions and bed geometries, which, together with sedimentary logs, palaeocurrent studies and outcrop-scale photomontages, enabled
interpretation and quantification of channel dimensions, internal architectures and stacking patterns. Based on these data, the Tullig Sandstone, a major sandbody within the Central Clare Group, is interpreted to be a low-sinuosity, braided fluvial system that flowed to the
north-northeast. This sandbody shows decreasing amounts of erosion and conglomeratic facies in both downstream and vertical directions, interpreted to reflect the combined effects of delta subsidence and sea-level rise over time, influencing the downstream reaches of the system first. The mean sand to non-sand ratio for the Tullig Sandstone is 97% by area, and connectivity of sandstone facies within this sandbody is 93%. In contrast, mouthbar sandbodies that were studied have a mean sand to non-sand ratio of 90%, and greatly reduced sandstone connectivity, at 65%. The data that characterise the field outcrops can be taken as
indicative of the probable characteristics of the El Wastani sandbodies.
The data generated from the quantitative field studies were used to construct computer models of the outcrops, in order to see how well the modelling software was able to reproduce the outcrop architectures and facies distributions, and also to test the sensitivity of the models to different scales of data. One large-scale model was built to include all the Tullig Sandstone outcrops along the coastline, with a vertical resolution (cell height) of 1m. A second smaller model was constructed to cover just the Trusklieve outcrop, and was built using a vertical cell height of O.1m. Each model was designed to fit the sedimentary log data, and was conditioned to reflect the facies percentages and channel dimensions measured and calculated respectively from the outcrops. The results showed that although the larger modelling grid,
with lower vertical and horizontal data resolution, showed significant differences in finegrained facies distribution from the outcrops, it was reasonably successful at reproducing the channel shapes and stacking patterns seen in outcrop. In addition, the high sand to non-sand
ratio meant that sandstone connectivity was not reduced compared with either the outcrops or the small, high-resolution model. The small model was better at reproducing the geometries of beds of fine-grained facies, but lacked the ability to accurately simulate the channel architectures and stacking patterns
Influence of contact area on the sliding friction and wear behaviour of an electrochemical jet textured Al-Si alloy
No full textEnvironmental legislation continues to drive optimisation of internal combustion engines in the automotive sector in an effort to reduce harmful emissions and promote fuel efficiency. Significant frictional losses occur at the ring pack, prompting research on reducing sliding friction at the ring – liner interface through the use of surface texturing. This study assesses the influence of contact area on the friction and wear behaviour of light-weight monolithic hyper-eutectic Al-Si alloy with a textured surface generated by electrochemical jet texturing. Flat rectangular samples were prepared from a cast cylinder liner via electro-discharge machining and flat lapped to 6 µm diamond finish prior to immersion in a 1 mol solution of NaOH for 120 s to simulate the mechanical honing process. Surfaces were electrochemically jet textured using a 2.3 mol solution of NaCl and current density of 220 A/cm2. An offset array of 1.3 × 0.3 mm rectangular features at 1.2 mm spacing was created with an average depth of 39 µm. Lubricated reciprocating sliding was carried out at a stroke length of 25 mm in a bath of PAO (4 cSt) at 100 °C against a 6 mm diameter, 13 mm long 52100 steel cylinder with three different contact areas corresponding to initial contact pressures of 157, 12 and 4 MPa. Sliding frequencies were varied between 1 and 15 Hz at a load of 50 N in order to establish the influence of both the contact pressure and velocity on the friction behaviour as a function of the lubrication regime. Textured features were observed to reduce the average coefficient of friction by up to 37% via a lubricant reservoir mechanism if the counter-surface contact width was greater than the feature dimension. Increases in contact pressure prevented a micro-EHL effect due to adhesive wear rather than pressurization of textured features
Toward more realistic viscosity measurements of tyre rubber–bitumen blends
No full textThe measurement of rheological properties of the tyre rubber bitumen blends is often challenging due to presence of suspended tyre rubber’s crumbs. Furthermore, the phase separation during the course of measurements makes the viscosity of these non-homogeneous blends difficult to ascertain. In this study, a new dual helical impeller was designed and manufactured to be used with a rotational viscometer in order to have a real-time control of the viscosity while performing a laboratory mixing of the blends. Layer based manufacturing techniques showed to be a convenient method to produce complex shaped impeller prototypes before manufacturing the more expensive stainless steel assembly. Impeller geometry was optimised to create a convective like flow within the sample and so minimise phase separation. Shear rate constant is geometry dependent and a calibration exercise was carried out to ascertain this. Results of both calibration and validation phases showed that the new impeller provides reliable viscosity measurements of homogenous fluids such as neat bitumen. With regards to complex fluids the new impeller showed a more stable and realistic trend than that obtained by using a standard spindle. In fact, it was demonstrated that the new impeller significantly decreases phase separation within the blend and in turns provides a more realistic measurement of the viscosity. This system represents a feasible and improved solution for optimising the laboratory modification process of tyre rubber bitumen blends by adapting the rotational viscometer as a low-shear mixer
Toponymical lexics in the pre-war period of A.T. Tvardovskiy’s creative work
No full textThe pre-war period (1926-1940) of A.T. Tvaedovskiy’s creative work, the great poet of the 20yh century, born in the Smolensk Region, is a period of his rising as an insuperable master of word, a people’s tribune, the time when the main traits of his poetry were developed and when his formation as a founder of the Smolensk Poetic School occurred. One of the central themes of the SPS poets, and first of all, A.T. Tvardovskiy himself, was the theme of “the minor” and “the big”. Motherland, which was materialized in significant motives through a system of toponyms. i.e. the names of geograpphical places. The article analyzes a system of macro- and mictrotoponyms and demonstrates their part in revealing of the thematical content of numerous pre-war poems (A Trip to Zagorye, 1939, Station Pochinok, 1936, and others), as well the first epical poem of the author Strana Muraviya (1936)
Driving next generation manufacturing through advanced metals characterisation capability
No full textUnderstanding the effects of manufacturing methods upon materials has driven constant innovation for over 300 years. While our ability to fabricate metallurgical wonders extends into the annals of history our ability to understand the scientific principles where process meets material has been pivotal to improving our capabilities. In this letter we briefly consider this history, comment upon the current state-of-the-art and, most importantly, propose new technologies for future industrial application which have been devised and exploited by the authors. It is hoped that this letter will allow other researchers to engage in this topic and facilitate the emergence of new processcompatible technologies which do not require destructive evaluation. This is particularly timely given the ability to manipulate microstructures with increasing dexterity. This is perhaps best illustrated in additive manufacturing [1] but is also a key consideration when process planning for machining [2], grinding [3] and forming [4].This article is published as Clare, A. T., M. Seita, A. Speidel, P. Collins, and M. Clark. "Driving next generation manufacturing through advanced metals characterisation capability." Scripta Materialia (2024): 116009. doi: https://doi.org/10.1016/j.scriptamat.2024.116009. © 2024 The Author(s). This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/)
- …
