Showing papers in "Materials Science and Technology in 2017"
TL;DR: In this paper, the Laves-phase formation in high-entropy alloys has been analyzed and shown that Laves phase formation in the produced and in the other HEAs, which are predominantly composed of Al and the elements of 4-6 groups and tend to form body-centred cubic solid solutions, can be predicted by the atomic size mismatch, δr, and the Allen electronegativity difference, ΔχAllen, parameters.
Abstract: In this study, we have analysed Laves-phase formation in high-entropy alloys (HEAs). For that purpose, the AlCrxNbTiV and AlxCrNbTiVZr (x = 0, 0.5, 1, 1.5) alloys were produced and examined. It was found that the AlNbTiV and AlCr0.5NbTiV alloys had single-phase body-centred cubic structure, while the other alloys contained Laves phase. Analysis has demonstrated that Laves-phase formation in the produced and in the other HEAs, which are predominantly composed of Al and the elements of 4–6 groups and tend to form body-centred cubic solid solutions, can be predicted by the atomic size mismatch, δr, and the Allen electronegativity difference, ΔχAllen, parameters. It was shown that Laves-phase formation is observed when δr > 5.0% and ΔχAllen > 7.0%.
130 citations
TL;DR: A review of additive manufacturing of metal components can be found in this article, where the influence of energy density on metallurgy, microstructure and mechanical properties of fabricated parts is addressed.
Abstract: Fabricating metallic components for highly specialised industries such as automotive and aerospace has become the main focus of additive manufacturing (AM) due to its many advantages over traditional processes. This review initially outlines current AM techniques for processing metallic components, particularly on ‘powder bed fusion’ and ‘directed energy deposition’ categories. Various solidification and metallurgical aspects, microstructure and properties of fabricated parts are described in subsequent sections. In addition, the influence of energy density on metallurgy, microstructure and mechanical properties is addressed. The need to establish processing maps for various materials and techniques, and the challenges currently faced in metal AM are then highlighted. The final section provides an outlook for the future of research in AM of metals.
125 citations
TL;DR: In this article, a review on the functionalisation of fullerenes for use in medical applications is presented, focusing on the need for safe and reproducible synthesis routes if they are ever going to make it to the pharmaceutical market.
Abstract: Research on fullerenes occupies a unique position in the scientific arena. Synthesis and characterisation of this nanomaterial blur the line between materials science and chemistry; careful tuning of the processing methods gives birth to a whole family of molecules and their functionalised derivatives, whose unusual properties at this nanoscopic scale can be exploited in cutting-edge technological applications. This review focuses on the functionalisation of fullerenes for use in medical applications. The first half gives an introduction to the fullerenes themselves and how their fundamental properties lead to a very rich chemistry, enabling both exohedral (external) and endohedral (internal) functionalisations of the cage. Emphasis is placed on the need for safe and reproducible synthesis routes if fullerenes are ever going to make it to the pharmaceutical market. In line with this, a selection of exohedral functionalisation protocols receives particular attention. Coverage of endohedral fullerene synthe...
108 citations
TL;DR: In this paper, the authors give an overview of recent progress in microstructure-specific hydrogen mapping techniques, including thermal desorption spectrometry, silver decoration, the hydrogen microprint technique, secondary ion mass spectroscopy, atom probe tomography, neutron radiography, and scanning Kelvin probe.
Abstract: This paper gives an overview of recent progress in microstructure-specific hydrogen mapping techniques. The challenging nature of mapping hydrogen with high spatial resolution, i.e. at the scale of finest microstructural features, led to the development of various methodologies: thermal desorption spectrometry, silver decoration, the hydrogen microprint technique, secondary ion mass spectroscopy, atom probe tomography, neutron radiography, and the scanning Kelvin probe. These techniques have different characteristics regarding spatial and temporal resolution associated with microstructure-sensitive hydrogen detection. Employing these techniques in a site-specific manner together with other microstructure probing methods enables multi-scale, quantitative, three-dimensional, high spatial, and kinetic resolution hydrogen mapping, depending on the specific multi-probe approaches used. Here, we present a brief overview of the specific characteristics of each method and the progress resulting from their...
106 citations
TL;DR: The formation of topologically close-packed (TCP) phases in nickel-base superalloys is an issue of increasing importance as alloys are designed with higher refractory element contents to meet the r....
Abstract: The formation of topologically close-packed (TCP) phases in nickel-base superalloys is an issue of increasing importance as alloys are designed with higher refractory element contents to meet the r...
84 citations
TL;DR: In this paper, the state-of-the-art manufacturing of titanium-based Ti-6Al-4V alloys by powder bed additive manufacture is examined. But, the authors focus on the structural properties of the powder-bed additive alloys.
Abstract: Additive manufacturing is currently a topic of considerable interest at both academic and industrial levels. While a significant amount of data exists on the mechanical properties and structure–property relationships of traditional wrought alloys, less information is available on alloys manufactured by additive manufacture. This review examines current state-of-the-art manufacture of titanium-based Ti–6Al–4V alloys by powder bed additive manufacture. Published mechanical properties to date are collected which include tensile strength, yield strength, hardness, wear, fracture toughness and fatigue. Differences in microstructure and properties compared to conventional wrought alloys of the same composition are described.
84 citations
TL;DR: A review of previous experimental and modelling work to establish the ability to predict the performance of tungsten in a fusion environment is presented in this article, with a focus on the difference in results from neutron and ion studies.
Abstract: Tungsten has been proposed for use in the divertor of future fusion devices. In this environment, it will be exposed to high heat fluxes, neutron damage and hydrogen and helium implantation. This review covers previous experimental and modelling work to establish our ability to predict the performance of tungsten in a fusion environment. Surrogates for high-energy neutrons have been used to predict the change in mechanical properties of tungsten, including fission neutron and self-ion exposure. These studies are critically analysed, with a focus on the difference in results from neutron and ion studies. Further studies to improve our ability to predict the performance of tungsten are proposed as a critical part of the path towards a working fusion reactor.This review was submitted as part of the 2016 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledgedVideo abstractRead the tra...
83 citations
TL;DR: In this article, a review of tube severe plastic deformation (SPD) processes intended to produce ultra-fine-grained and nanostructured tubes, and their effects on material properties is presented.
Abstract: Severe plastic deformation (SPD) is known to be the best method for producing bulk ultrafine-grained and nanostructured materials with excellent properties. Different SPD methods were developed that are suitable for sheet and bulk solid materials. During the past decade, efforts have been made to create effective SPD processes suitable for producing cylindrical tubes. In this paper, we review SPD processes intended to produce ultrafine-grained and nanostructured tubes, and their effects on material properties. The paper will focus on introduction of the tube SPD processes, and then comparison of them based on their advantages and disadvantages from the viewpoints of processing and properties.
82 citations
TL;DR: In this article, a review of the Austenite-reverted-transformation annealing treatment routine, mechanical properties and deformation mechanisms and effect of heat treatment on microstructure and mechanical properties of medium-Mn steels are summarised.
Abstract: In the automotive industry, the current development trend of lightweight and low-emission vehicles requests for high-performance materials. Benefiting from an excellent balance of mechanical properties and production cost, medium-Mn steels have attracted extensive interest by materials scientists. Austenite-reverted-transformation annealing plays a vital role in stabilisation of retained austenite and grain refinement, resulting in a considerable amount of retained austenite. Localised deformation phenomenon is usually observed in the ultrafine-grained medium-Mn steels owing to the absence of strain hardening. The occurrence of transformation-induced-plasticity and/or twinning-induced-plasticity effect in austenite improves strain hardening effectively. In the current review, austenite-reverted-transformation annealing treatment routine, mechanical properties and deformation mechanisms and effect of heat treatment on microstructure and mechanical properties of medium-Mn steels are summarised.This ...
80 citations
TL;DR: In this article, the results and data presented in this paper have been obtained within the ExoMet Project funded by the EC/FP7 (contract FP7-NMP3-LA-2012-280421); the Doshormat Project (grant agreement 606090); UltraMelt project (contract number EP/K005804/1) and UltraCast project (construction contract No EP/L019884/1).
Abstract: The results and data presented in this paper have been obtained within the ExoMet Project funded by the EC/FP7 (contract FP7-NMP3-LA-2012-280421); the Doshormat Project funded by the EC/FP7 (grant agreement 606090); UltraMelt project (contract number EP/K005804/1) and UltraCast project (contract number EP/L019884/1) funded by EPSRC.
77 citations
TL;DR: In this paper, a critical assessment highlights the current understating regarding factors affecting the joint properties and approaches to control the interfacial reaction and unresolved scientific challenges are discussed with the goal of shedding light on the path forward to produce reliable metallurgical bonding between aluminium and steels for automotive application.
Abstract: Dissimilar joining of aluminium and steel, especially using resistance spot welding as a critical process in vehicle manufacturing, is a key challenge for multi-materials lightweight design strategy. Controlling the formation and growth of Al5Fe2 intermetallic is the outstanding issue for producing high strength crash-resistance Al/steel dissimilar resistance spot welds. This critical assessment highlights the current understating regarding factors affecting the joint properties and approaches to control the interfacial reaction. Finally, the unresolved scientific challenges are discussed with the goal of shedding light on the path forward to produce reliable metallurgical bonding between aluminium and steels for automotive application.
TL;DR: In this article, a carbide-containing FeCoCrNiMn alloy was prepared by arc melting, and its microstructure and mechanical properties were further tuned by cold rolling with subsequent annealing treatment.
Abstract: Previous studies have reported that high carbon contents in FeCoCrNiMn high-entropy alloys lead to carbides precipitating from the alloys. Typically, carbides are used to improve the strength of alloys but also lead to decreased ductility. However, the strength and ductility of alloys can be improved when carbides shape, size and distribution are carefully controlled. Therefore, a carbide-containing FeCoCrNiMn alloy with 2 at.-% carbon was prepared by arc melting, and its microstructure and mechanical properties were further tuned by cold rolling with subsequent annealing treatment. The yield strength and uniform elongation of the resultant alloy were excellent, reaching 581 MPa and 25%, respectively, due to the additive combination of various strengthening mechanisms, such as solid-solution hardening, grain-boundary hardening and precipitation hardening.
TL;DR: In this paper, a thermochemical process followed by powder metallurgy technique was used to produce a Cu-ZrO2 nanocomposites with X-ray diffracting.
Abstract: Cu–ZrO2 nanocomposites were produced by the thermochemical process followed by powder metallurgy technique. Microstructure development during fabrication process was investigated by X-ray diffracti...
TL;DR: Grain boundary precipitates in Inconel 718 and ATI 718 plus are important to control during hot working processes, since they can control the grain size as discussed by the authors, which can lead to excessive or insufficient amou...
Abstract: Grain boundary precipitates in Inconel 718 and ATI 718Plus are important to control during hot working processes, since they can control the grain size. Precipitating excessive or insufficient amou...
TL;DR: In this article, the microstructural and crystallographic features of hydrogen-related fracture under tensile deformation in martensitic steels were summarized, and the fracture surfaces consisted of facets parallel to the {011} planes on a microscopic level.
Abstract: This paper summarised the microstructural and crystallographic features of hydrogen-related fracture under tensile deformation in martensitic steels. The specimens with relatively low strength exhibited quasi-cleavage fracture. Crystallographic orientation analysis demonstrated that the quasi-cleavage fracture occurred on {011} planes. On the other hand, the macroscopic fracture surface morphologies of the specimens with relatively high strength appeared to be intergranular-like. However, nature of the fracture was somewhat different from a typical intergranular fracture, and the fracture surfaces consisted of facets parallel to {011} planes on a microscopic level. Based on the experimental results, we concluded that the crystallographic feature of {011} plane itself had an important role on the hydrogen-related fracture.This paper is part of a thematic issue on Hydrogen in Metallic Alloys
TL;DR: In this paper, the authors have discussed the mechanism of catalysis and factors affecting the rate of catalytic activity of hybrid microgels and possible future studies for further development in this area have been also predicted.
Abstract: Temperature-responsive hybrid microgels have been extensively used as catalyst for degradation of toxic chemicals in the last 10 years. Various architectures of such kind of hybrid microgels with tunable catalytic activity have been reported in literature. Recent research progress in synthesis, characterisation and catalytic applications of various hybrid microgels based on N-isopropylacrylamide has been described critically in this article. Mechanism of catalysis and factors affecting the rate of catalysis by hybrid microgels have been discussed in the light of research done in this area. Possible future studies for further development in this area have been also predicted in this article.
TL;DR: In this paper, the authors reviewed the available interatomic interaction potentials for iron, which describe the properties of different phases present in that system, and gave insight on the mechanisms of the nucleation and growth of bcc phase in iron.
Abstract: Molecular dynamics (MD) simulation has been used to study the martensitic transformation in iron at the atomic scale. The paper reviews the available interatomic interaction potentials for iron, which describe the properties of different phases present in that system. Cases on the fcc-to-bcc transformation in iron by MD simulations were included in the present paper. Factors affecting the fcc-to-bcc transformation in iron were analysed: (a) structural factors, such as grain/phase boundaries, grain sizes and stacking faults; (b) simulation conditions, such as the presence of free surfaces, external stress/strain and studied temperatures; (c) the interatomic interaction potential. The main emphasis of the present paper is on results giving insight on the mechanisms of the nucleation and growth of bcc phase in iron.This review was submitted as part of the 2016 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TW...
TL;DR: In this article, the authors reviewed the available data on the effects of radiation, notably neutron radiation, on nickel-based alloys and discussed the possible mitigation strategies and design opportunities for radiation embrittlement-resistant alloys based on recent developments in alloy computational design.
Abstract: The effects of neutron radiation on nickel-based alloys in thermal reactors are defying predictions that were made based upon accelerated testing in fast reactors. As nickel-based alloy components face significant doses in aging thermal reactors and their role in Gen-IV reactor designs becomes prominent, the literature on the effects of radiation on such alloys must be reviewed to enable better structural integrity assessments for relevant components and optimise alloys with respect to irradiation embrittlement resistance. This paper reviews the available data on the effects of radiation, notably neutron radiation, on nickel-based alloys and discusses the possible mitigation strategies and design opportunities for radiation embrittlement-resistant alloys based on recent developments in alloy computational design.This review was submitted as part of the 2016 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TW...
TL;DR: In this article, the benefits and challenges associated with phase change random access memory (PCRAM) are comprehensively taken stock, while reasoning the need for a switch to a newer data storage technology, and comparing PCRAM with other data storage and computation platforms.
Abstract: Having monopolised the optical data storage industry since the very beginning, phase change materials are now being intensively explored for next-generation electronic data storage, referred to as phase change random access memory (PCRAM). Because phase change materials are electrically programmable; capable of reversibly switching between two stable structural phases of contrasting electrical properties, besides data storage they also enable data computation. For these reasons, PCRAM envisages to overcome both miniaturisation and data flow bottlenecks, challenges which current silicon charge-based technology is failing to cope with. This review, while reasoning the need for a switch to a newer data storage technology, and comparing PCRAM with other data storage and computation platforms, comprehensively takes stock of the benefits and challenges associated with PCRAM. This review also critically investigates and associates the materials science and physics, such as the atomic structure and bondin...
TL;DR: In this paper, the microstructure and wear resistance of the amorphous coatings were comparatively studied, and the wear volume loss of the AC-HVAF coating is approximately seven times less than that of the HVOF coating.
Abstract: Fe63Cr8Mo3.5Ni5P10B4C4Si2.5 amorphous coatings have been prepared by the activated combustion high velocity air fuel (AC-HVAF) and high velocity oxygen fuel (HVOF) processes. The microstructure and wear resistance of the amorphous coatings are comparatively studied. The wear volume loss of the AC-HVAF coating is approximately seven times less than that of the HVOF coating, indicating that the AC-HVAF coating exhibits better wear resistance. Detailed analysis on the worn surface indicates that the enhanced wear resistance of the AC-HVAF coating is mainly attributed to the formation of a more stable oxide tribolayer and smoother worn surface, which result from the dense and complete amorphous microstructure of the AC-HVAF coating. The wear mechanism of the amorphous coatings is dominated by oxidation wear.
TL;DR: Selective laser melting (SLM) is a form of additive manufacturing technology that makes it possible to create complex parts directly from metal powders as mentioned in this paper, which offers a good balance betwee...
Abstract: Selective laser melting (SLM) is a form of additive manufacturing technology that makes it possible to create complex parts directly from metal powders. This technology offers a good balance betwee...
TL;DR: The winner of the 2017 Materials Literature Review Prize as discussed by the authors was chosen as a runner-up of the 2018 edition of the prize, which was run by the Institute of Materials, Minerals and Mining (MST).
Abstract: Photocatalytic conversion of CO2 to valuable chemicals by solar irradiation is a hugely attractive process due to its potential to offset both the energy and economic penalties of CO2 capture and sequestration. Metal-organic frameworks (MOFs) have recently been explored as photocatalysts for this processing owing to their promising photochemical and textural properties. Papers to date are collated and reviewed to highlight advances made in MOF photocatalysts through novel synthesis and analytical methods. These are compared with key metrics highlighting the range of materials and methods used to show the diversity and novelty of this emerging field. Knowledge gaps were noted in order to propose potential routes for further improvements in catalyst and reactor design.This review was chosen as a runner up of the 2017 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining, run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged
TL;DR: In this article, cold deformation was applied to Armco pure iron to increase dislocation density and modify grain boundary characteristics, and the hydrogen diffusivity decreased as the hydrogen trapping ability of the microstructure increased.
Abstract: The goal of this study is to obtain a deeper insight in the relation between hydrogen diffusion and hydrogen traps present in Armco pure iron. Cold deformation was applied to this material, which initially contained a limited amount of traps. The cold deformation was applied to increase the dislocation density and modify grain boundary characteristics. In this way, the hydrogen diffusivity decreased as the hydrogen trapping ability of the microstructure increased. A subsequent heat treatment allowed changing the density of microstructural defects again and consequently increased the hydrogen diffusion coefficient. In addition, studying blister formation showed that a higher degree of deformation caused more surface blisters, while recovery lowered the number of blisters. Electron backscatter diffraction characterisation provided the necessary input on the microstructural features and their evolution. Analysis of these samples allowed evaluating the correlation between hydrogen diffusion, blister f...
TL;DR: In this paper, the effective Young's modulus of aluminium matrix syntactic foams was determined by modal analysis and three different analytical methods were studied to estimate the Youngs modulus.
Abstract: The effective Young’s modulus of aluminium matrix syntactic foams was determined by modal analysis. Two different matrix materials (Al99.5 and AlSi12) were used, and they were reinforced by Globocer grade ceramic hollow spheres. In order to validate the results, a full-scale finite element model was also created. A new algorithm was developed to place the spheres in a proper, probabilistic spatial distribution. Finite element simulations were carried out in modal analysis and compression test senses. In addition, three different analytical methods were studied to estimate the effective Young’s modulus. The measured values were compared with the finite element and analytical results. The determined effective Young’s moduli showed good agreement.
TL;DR: In this article, all the main aspects associated with the use of field-assisted sintering techniques are presented and discussed, with particular emphasis on spark-plasmination.
Abstract: The interest towards field-assisted sintering techniques has been growing rapidly in the last 20 years, particularly in applications involving hard to sinter materials, such as nanocrystalline, refractory, and metastable materials. These techniques, in fact, allow obtaining the densification in conditions that are considerably milder than in traditional pressureless sintering or in hot-pressing. Despite this success, there is still a poor understanding of the involved basic mechanisms. In this assessment, all the main aspects associated with the use of these technique will be presented and discussed, with particular emphasis on spark plasma sintering.
TL;DR: In this article, the progress in the mechanical properties of WC-Fe alloys hardmetals is reviewed, including the transverse rupture strength properties of these composites with further development in the microstructural parameters such as porosity during sintering.
Abstract: Growing concerns over the use of cobalt as binder for WC-based hardmetals has directed research efforts towards finding a suitable alternative binder offering comparable or even superior properties than those found in WC–Co hardmetals. Complete substitution of cobalt by iron alloys has been extensively explored in several studies with significant improvements in mechanical properties of WC bonded with Fe alloys when carbon content addition is strictly controlled in powder composition. Asides from the commonly studied hardness and fracture toughness properties, transverse rupture strength property of this composites has also been observed to hold future promise with further development in the microstructural parameters such as porosity during sintering. This article reviews the progress in the mechanical properties of WC–Fe alloys hardmetals.
TL;DR: In this article, high-temperature tensile tests were performed at different temperatures and after different solid solution treatments to investigate the effect of Cr-rich M23C6, Nb-rich MC and the delta phase on the mechanical properties of Inconel 625.
Abstract: Based on the temperature sensitivity characteristics, high-temperature tensile tests were performed at different temperatures and after different solid solution treatments to investigate the effect of Cr-rich M23C6, Nb-rich MC and the delta phase on the mechanical properties of Inconel 625. The experimental results indicated that the Cr-rich M23C6 carbides and the Nb-rich MC carbides decomposed at 700°C, which could be the reason for resulting tensile strength anomaly that was observed in a narrow temperature range from 650 to 700°C during the tensile tests at different temperatures. For the samples subjected to a prior solid solution treatment, the size of the δ phase was found to increase with the solution treatment temperature, whereas the elongation at fracture decreased.
TL;DR: In this article, the stacking fault energy (SFE) was taken into account and three FCC materials possessing different SFEs were strained in electrically assisted uniaxial tension under continuous current application.
Abstract: Electrically assisted manufacturing is based on the electro-plastic effect induced by electricity on the material flow during deformation and represents an alternative method for forming materials. Several studies have pointed out the real effectiveness of this technique, but no relations among microstructure, electrical resistivity, crystal structure and deformation-mode have been revealed. In the present work, the stacking fault energy (SFE) was taken into account and three FCC materials possessing different SFEs were strained in electrically assisted uniaxial tension under continuous current application. The results showed an advantageous electric contribution only in the highest SFE material, whereas no enhancements in formability were revealed in the investigated low- and intermediate-SFE metals.
TL;DR: In this article, the authors compared two approaches to study acicular ferrite formation in a titanium-deoxidised high-strength low-alloyed steel and its influencing factors on laboratory scale.
Abstract: By increasing the amount of acicular ferrite (AF) in the microstructure, steel toughness can be improved significantly. The steel composition, cooling rate, non-metallic inclusions and austenite grain size have a strong influence on the formation of AF. The present paper describes and compares two approaches to study AF formation in a titanium-deoxidised high-strength low-alloyed steel and its influencing factors on laboratory scale: route A simulates the formation of AF after heat treatment; route B simulates the formation directly after solidification of the melt. The formation of AF is essentially influenced by the former processing, which also changes the optimum cooling parameters substantially. (Ti,Mn)xOy and (Ti,Al,Mn)xOySz are the predominant active inclusion types in the investigated steel.
TL;DR: Nickel superalloys exhibit a remarkable characteristic that their yield stress that required to cause the onset of plastic deformation increases with temperature as discussed by the authors, and it is generally accepted that this is caused by the exhaustion of dislocations by cross-slip from {111} glide planes to {010} planes on which they are sessile.
Abstract: Nickel superalloys exhibit a remarkable characteristic. Their yield stress that required to cause the onset of plastic deformation increases with temperature. This typically occurs up to a temperature of around 800°C. This effect is thought to originate from the precipitates of the microstructure, which have an L12-ordered crystal structure. A number of other L12-based alloys exhibit similar yield properties. It is generally accepted that this is caused by the exhaustion of dislocations by cross-slip from {111} glide planes to {010} planes on which they are sessile. However, the underlying mechanisms that control this cross-slipping process are yet to be fully understood, with little consistency between empirical results and theory. A critical review of the various theories surrounding nickel superalloys is offered.