Showing papers in "International Materials Reviews in 2016"
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TL;DR: In this article, a review of additive manufacturing (AM) techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy.
Abstract: Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.
1,713 citations
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TL;DR: In this article, a review of the relationship between process characteristics, material consolidation and the resulting materials and component properties is presented, with a special focus on the relationship of process characteristics and material consolidation.
Abstract: Selective electron beam melting (SEBM) belongs to the additive manufacturing technologies which are believed to revolutionise future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high power electron beam. In contrast to selective laser melting (SLM), which can be used for metals, polymers and ceramics, the application field of the electron beam is restricted to metallic components since electric conductivity is required. On the other hand, the electron beam works under vacuum conditions, can be moved at extremely high velocities and a high beam power is available. These features make SEBM especially interesting for the processing of high-performance alloys. The present review describes SEBM with special focus on the relationship between process characteristics, material consolidation and the resulting materials and component properties.
642 citations
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TL;DR: In this article, the effect of entropic stabilisation of solid solutions, the severe distortion of their lattices, the sluggish diffusion kinetics and the properties derived from a cocktail effect of high-entropy alloys are investigated.
Abstract: High-entropy alloys (HEAs) are a relatively new class of materials that have gained considerable attention from the metallurgical research community over recent years They are characterised by their unconventional compositions, in that they are not based around a single major component, but rather comprise multiple principal alloying elements Four core effects have been proposed in HEAs: (1) the entropic stabilisation of solid solutions, (2) the severe distortion of their lattices, (3) sluggish diffusion kinetics and (4) that properties are derived from a cocktail effect By assessing these claims on the basis of existing experimental evidence in the literature, as well as classical metallurgical understanding, it is concluded that the significance of these effects may not be as great as initially believed The effect of entropic stabilisation does not appear to be overarching, insufficient evidence exists to establish the strain in the lattices of HEAs, and rapid precipitation observed in some HEAs sug
604 citations
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TL;DR: In this paper, the authors gather the grain-size strengthening data from the Hall-Petch studies on pure metals and use this aggregated data to calculate best estimates of these metals' Hall-petch parameters.
Abstract: Refining a metal’s grain size can result in dramatic increases in strength, and the magnitude of this strengthening increment can be estimated using the Hall–Petch equation. Since the Hall–Petch equation was proposed, there have been many experimental studies supporting its applicability to pure metals, intermetallics and multi-phase alloys. In this article, we gather the grain-size strengthening data from the Hall–Petch studies on pure metals and use this aggregated data to calculate best estimates of these metals’ Hall–Petch parameters. We also use this aggregated data to re-evaluate the various models developed to physically support the Hall–Petch scaling.
523 citations
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TL;DR: In this paper, the authors summarise the recent progress in bulk thermoelectric (TE) materials and summarize the recently achieved enhancements in the TE performance encompassing the use of electronic band structure engineering, lattice phon...
Abstract: Thermoelectric (TE) materials facilitate direct heat-to-electricity conversion. The performance of a TE material is characterised by its figure of merit zT (=S2 σT/κ) that depends on both electronic transport properties, i.e. the Seebeck coefficient S and the electrical conductivity σ, and on thermal transport properties, i.e. the thermal conductivity κ of a material. The intrinsically counter-correlated behaviour between electronic and thermal transport properties makes the enhancement of zT a very challenging task. In the past 10 years, the zTs in bulk TE materials have been significantly enhanced due to intensive exploratory efforts, the discovery of new physical phenomena and effects, and applications of advanced synthesis methods. In this review, we summarise the recent progress in bulk TE materials. After the introduction of fundamental principles of thermoelectricity, the recently achieved enhancements in the TE performance encompassing the use of electronic band structure engineering, lattice phon...
380 citations
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TL;DR: In this paper, the current state of understanding and development of RFW and LFW is presented, focusing on the process parameters, joint microstructure, residual stresses, mechanical properties and their relationships.
Abstract: Friction welding (FW) is a high quality, nominally solid-state joining process, which produces welds of high structural integrity. Rotary friction welding (RFW) is the most commonly used form of FW, while linear friction welding (LFW) is a relatively new method being used mainly for the production of integrally bladed disc (blisk) assemblies in the aircraft engine industry. Numerous similar and dissimilar joints of structural metallic materials have been welded with RFW and LFW. In this review, the current state of understanding and development of RFW and LFW is presented. Particular emphasis is placed on the process parameters, joint microstructure, residual stresses, mechanical properties and their relationships. Finally, opportunities for further research and development of the RFW and LFW processes are identified.
220 citations
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TL;DR: This review summarises the unique properties of various composite biomaterial scaffolds and highlights their advantages over other pristine scaffolds for engineering functional three-dimensional cardiac patches.
Abstract: Coronary heart diseases result from the blockage of one of the coronary arteries, which nourishes the heart muscle. This process leads to ischaemia of a segment of the heart and death of the contractile tissue. As cardiac tissue is unable to regenerate itself, heart function is impaired. Tissue engineering (TE) is a field of science that integrates knowledge from biology, materials sciences, engineering and medicine to develop artificial, functional tissue constructs to replace defected tissues. In cardiac TE, contracting cells are seeded within supporting biomaterial scaffolds that provide them with the essential microenvironment for functional tissue assembly. Various strategies and methods for fabricating these scaffolds have been proposed and tested in the last decade, some of which combine multiple elements that altogether contribute to the formation of an improved functional tissue. This review summarises the unique properties of various composite biomaterial scaffolds and highlights their advantage...
100 citations
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TL;DR: In this paper, a review of the most important graphite properties which change with exposure to irradiation, namely dimens, dimens and degrades, is presented. But the graphite core components are not considered in this paper.
Abstract: Since the start of the ‘nuclear age’ graphite has been employed as a moderator in around 100 nuclear reactors, and today there are still some 30 graphite-moderated reactors operating and there are plans for new Generation IV high-temperature reactors. Many of the graphite moderator reactors now producing power are operating beyond their original design life. Therefore in some cases, to aid the reactor operators and designers, the existing graphite irradiation databases need to be extended either to a higher temperature or higher neutron fluence. Furthermore, data are needed for the different grades of graphite that are available at present. This can either be achieved by expensive, time consuming irradiation programmes or by improving the understanding of the mechanisms and processes which lead to irradiation-induced dimensional and property changes in the graphite core components. This review looks at three of the most important graphite properties which change with exposure to irradiation, namely dimens...
95 citations
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TL;DR: In this paper, a review of cold spray material deposition can be found for applications with heat sensitive substrates or those applications that do not allow heat-modified deposits, as well as applications that require high strength, low porosity and minimal or compressive residual stress.
Abstract: Cold spray material deposition differs significantly from other thermal spray systems in that the cold spray process does not melt particles, particle velocities are very high, and the gas/particle jet plume has a relatively low temperature. Cold spray can thus be applied to applications with heat-sensitive substrates or those applications that do not allow heat-modified deposits. The impact consolidation of high velocity, solid state, particles yield cold spray depositions with high strength, low porosity and minimal or compressive residual stress. This review will be useful to individuals new to cold spray, as well as to the cold spraying community and to product developers needing cold spray capability. The applications presented here can demonstrate capabilities that are of use to new and related uses. The descriptions of the equipment and techniques used to create the cold-sprayed deposits will be helpful to those individuals and firms seeking to produce products requiring similar characteristics.
93 citations
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TL;DR: Piezoresponse force microscopy (PFM) has been used to probe electromechanical functionality in a wide range of piezoelectric materials including organic and biological systems.
Abstract: Piezoresponse force microscopy (PFM) probes the mechanical deformation of a sample in response to an electric field applied with the tip of an atomic force microscope. Originally developed more than two decades ago to study ferroelectric materials, this technique has since been used to probe electromechanical functionality in a wide range of piezoelectric materials including organic and biological systems. Piezoresponse force microscopy has also been demonstrated as a useful tool to detect mechanical strain originating from electrical phenomena in non-piezoelectric materials. Parallelling advances in analytical and numerical modelling, many technical improvements have been made in the last decade: switching spectroscopy PFM allows the polarisation switching properties of ferroelectrics to be resolved in real space with nanometric resolution, while dual ac resonance tracking and band excitation PFM have been used to improve the signal-to-noise ratio. In turn, these advances have led to increasingly large m...
86 citations
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TL;DR: It is elucidated here process–structure–property relationships in implantable biomaterials processed by rapid prototyping approaches that are based on the principle of additive manufacturing that are potentially attractive for biomedical devices.
Abstract: We elucidate here process–structure–property relationships in implantable biomaterials processed by rapid prototyping approaches that are based on the principle of additive manufacturing. The conventional methods of fabrication of biomedical devices including freeze casting and sintering are limited because of difficulties in adaptation at the host site and mismatch in micro/macrostructure, mechanical and physical properties with the host tissue. Moreover, additive manufacturing has the advantage of fabricating patient-specific designs, which can be obtained from the computed tomography scan of the defect site. The discussion here comprises two parts – the first part briefly describes the evolution and underlying reasons that have led to 3D printing of scaffolds for tissue regeneration. The second part focuses on biocompatibility and mechanical properties of 3D scaffolds, fabricated by different approaches. The article concludes with a discussion on functionally graded scaffolds and vascularisation of 3D ...
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TL;DR: Scandium metallurgy is still a largely unexplored field as mentioned in this paper, but progress is being made in the last decade and the use of scandium as a conventional minor addition to alloys, largely in structural applications, is described.
Abstract: Despite its excellent elemental properties, lightweight nature and good alloying potential, scandium has received relatively little attention in the manufacturing community. The abundance of scandium in the Earth's crust is quite high. It is more abundant than silver, cobalt, lead and tin. But, because scandium is so well dispersed in the lithosphere, it is notoriously difficult to extract in commercial quantities – hence low market availability and high cost. Scandium metallurgy is still a largely unexplored field – but progress is being made. This review aims to summarise advances in scandium metallurgical research over the last decade. The use of scandium as a conventional minor addition to alloys, largely in structural applications, is described. Also, more futuristic functional applications are discussed where details of crystal structures and peculiar symmetries are often of major importance. This review also includes data obtained from more obscure sources (especially Russian publications) which ar...
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TL;DR: High-speed atomic force microscopy (HS-AFM) as discussed by the authors can achieve megapixels per second over scan areas of square millimetres, removing the limitations from AFM for industrial scale materials characterisation.
Abstract: Since its inception in 1986, the field of atomic force microscopy (AFM) has enabled surface analysis and characterisation with unparalleled resolution in a wide variety of environments. However, the technique is limited by very low sample throughput and temporal resolution making it impractical for materials science research on macro sized or time evolving samples such as the observation of corrosion. The potential of AFM sparked intense efforts to overcome these limitations shortly after its invention, and has led to the development of high-speed atomic force microscopes (HS-AFMs). Within the last 5 years the technology underpinning these instruments has matured to the point where routine imaging can achieve megapixels per second over scan areas of square millimetres, removing the limitations from AFM for industrial scale materials characterisation. This review explains the technology and looks to the future use of HS-AFMs in materials science.
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TL;DR: The present work in spintronics at most of the mainstream semiconductor companies and foundaries is focused on the development of perpendicular STT-MRAM, as a universal memory that can compete with the mainstream memories and surpass them in several key metrics.
Abstract: Spintronics has emerged in the last two decades as both an extremely fruitful direction of research into the properties and usefulness of the spin degree of freedom of the electron as it can apply to the exponentially expanding world of electronics. Spintronics has infiltrated almost every household in the form of the read head sensors for the hard drives that inhabit every desktop and most laptop computers. Embedded magnetic random access memory (MRAM) and in-plane STT-RAM are rapidly replacing SRAM in a host of applications that do not require ultra-dense memories. Soon these embedded spintronic memories will permeate the cell phone market because they are much denser than SRAM, offer lower power at only slightly lower speed and are non-volatile. The present work in spintronics at most of the mainstream semiconductor companies and foundaries is focused on the development of perpendicular STT-MRAM, as a universal memory that can compete with the mainstream memories and surpass them in several key metrics...
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TL;DR: A review pertaining to advances and developments since 2011, summarise progress on fabrication, design and understanding of all the existing concepts for obtaining materials that are oil-repellent including smooth oleophobic materials, textured superoleophobic and superomniphobic surfaces, and lubricated porous/textured substrates as discussed by the authors.
Abstract: During the last years, emerging research has focused on the development and design of novel materials that can successfully repel oils and other liquids. In order to achieve such properties, different fabrication strategies can be followed. Up to now, several reviews have been published that focus and investigate each of these concepts individually without giving an entire overview of all the existing approaches for achieving oil-repellency. In this review pertaining to advances and developments since 2011, we summarise progress on fabrication, design and understanding of all the existing concepts for obtaining materials that are oil-repellent including smooth oleophobic materials, textured superoleophobic and superomniphobic surfaces, and lubricated porous/textured substrates. In each of these categories, we highlight the most successful methods to produce oil-repellent surfaces while their applications are also demonstrated. Finally, recent studies and new trends focusing on the development of oil-repel...
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TL;DR: Spider silk exhibits remarkable properties, especially its well-known tensile performances, which rely on a complex nanostructured hierarchical organization that studies progressively elucidate as mentioned in this paper. But the full understanding of the relation between structure and properties may lead in the future to the design of a variety of high-performance, tailored materials and devices.
Abstract: Spider silk exhibits remarkable properties, especially its well-known tensile performances. They rely on a complex nanostructured hierarchical organisation that studies progressively elucidate. Spider silk encompasses a vast range of fibres that exhibit diverse and captivating physical and biological characteristics. The full understanding of the relation between structure and properties may lead in the future to the design of a variety of high-performance, tailored materials and devices. Reknown for being produced in mild and benign conditions, this outstanding biological material constitutes one of the more representative example of biomimetism. In addition, silk's structure is produced with limited means, i.e. low energy and relatively simple renewable constituents (silk proteins). Then, if successfully controlled and adequately transposed in biomaterials, some properties of natural silk could lead to innovative green materials that may contribute to reduce the ecological footprint of societies. In fac...
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TL;DR: A review of cable architecture and stress states experienced during testing is followed by an overview of the effects of changes in material composition, microstructure, processing and test conditions on fracture and fatigue behaviour of wire and cable systems used in biomedical applications.
Abstract: Fine wires and cables play a critical role in the design of medical devices and subsequent treatment of a large array of medical diagnoses. Devices such as guide wires, catheters, pacemakers, stents, staples, functional electrical stimulation systems, eyeglass frames and orthodontic braces can be comprised of wires with diameters ranging from 10s to 100s of micrometres. Reliability is paramount as part of either internal or external treatment modalities. While the incidence of verified fractures in many of these devices is quite low, the criticality of these components requires a strong understanding of the factors controlling the fracture and fatigue behaviour.1,2 Additionally, optimisation of the performance and reliability of these devices necessitates characterisation of the fatigue and fracture properties of its constituent wires. A review of cable architecture and stress states experienced during testing is followed by an overview of the effects of changes in material composition, microstructure, pr...
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TL;DR: In this paper, a review of polymer patterning in silicon photovoltaics is presented, where patterning is required for selective doping etching and metallisation, which has resulted in the average energy conversion efficiencies of industrially produced cells remaining on average 5% lower than the value of 25% reported in 1999 for cells patterned with optical lithography.
Abstract: Patterning is fundamental to advancing most technologies. Although the challenge for electronic integrated circuits continues to be reduced feature size other applications have different requirements and challenges. This review contributes insights from silicon photovoltaics where patterning is required for selective doping etching and metallisation. Earlier silicon solar cell devices extensively used optical lithography to fabricate devices in the laboratory with high device efficiencies being achieved. However industrial cell fabrication has largely relied on uniformly doped silicon layers and lower resolution screen-printing for metal electrode formation because optical lithography is considered too expensive and slow. This has resulted in the average energy conversion efficiencies of industrially produced cells remaining on average 5% lower than the value of 25% reported in 1999 for cells patterned with optical lithography. Motivated by the goal of bridging this efficiency gap many new polymer pattern...