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Showing papers in "International Materials Reviews in 2012"


Journal ArticleDOI
TL;DR: Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser as discussed by the authors, which is based on a novel materials incremental manufacturing philosophy.
Abstract: Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

2,402 citations


Journal ArticleDOI
TL;DR: Porous ceramics are now expected to be used for a wide variety of industrial applications from filtration, absorption, catalysts, and catalyst supports to lightweight structural components as mentioned in this paper.
Abstract: Porous ceramics are now expected to be used for a wide variety of industrial applications from filtration, absorption, catalysts and catalyst supports to lightweight structural components. During the last decade, tremendous efforts have been devoted for the researches on innovative processing technologies of porous ceramics, resulting in better control of the porous structures and substantial improvements of the properties. This article intends to review these recent progresses of porous ceramics. Because of a vast amount of research works reported in this field these days, the review mainly focuses on macro-porous ceramics whose pore size is larger than 50 nm. Followed by giving a general classification of porous ceramics, a number of innovative processing routes developed for critical control of pores are described, along with some important properties. The processes are divided into four categories including (i) partial sintering, (ii) sacrificial fugitives, (iii) replica templates and (iv) dir...

514 citations


Journal ArticleDOI
TL;DR: In this article, the authors review the existing knowledge base on the fatigue of Nitinol, both in terms of their stress or strain life (total life) and damage tolerant (crack propagation) behaviour, together with their fracture toughness properties.
Abstract: Nitinol, a near equiatomic intermetallic of nickel and titanium, is the most widely known and used shape memory alloy. Owing to its capacity to undergo a thermal or stress induced martensitic phase transformation, Nitinol displays recoverable strains that are more than an order of magnitude greater than in traditional alloys, specifically as high as 10%. Since its discovery in the 1960s, Nitinol has been used for its shape memory properties for couplings and actuators, although its contemporary use has been in for medical devices. For these applications, the stress induced transformation (‘superelasticity’) has been used extensively for self-expanding implantable devices such as endovascular stents and vena cava filters, and for tools such as endodontic files. Most of these applications involve cyclically varying biomechanical stresses or strains that drive the need to fully understand the fatigue and fracture resistance of this alloy. Here we review the existing knowledge base on the fatigue of Nitinol, both in terms of their stress or strain life (total life) and damage tolerant (crack propagation) behaviour, together with their fracture toughness properties. We further discuss the application of such data to the fatigue design and life prediction methodologies for Nitinol implant devices used in the medical industry.

317 citations


Journal ArticleDOI
TL;DR: In this article, the fundamental principles of the porous microstructure evolution and critical factors that influence the fundamental physics involved in freeze casting of particulate suspensions are discussed, including the effects of additives, freezing conditions, suspension solids loading and particle size on pore shape, size and morphology evolution.
Abstract: Freeze casting is a promising technique to fabricate porous materials with complex pore shapes and component geometries. This review is aimed to elaborate the fundamental principles of the porous microstructure evolution and critical factors that influence the fundamental physics involved in freeze casting of particulate suspensions. The discussion separately analyses homogeneous and directional freeze casting for both aqueous and non-aqueous systems. The effects of additives, freezing conditions, suspension solids loading and particle size on pore shape, size and morphology evolution are discussed. Special techniques based on modified freeze casting, such as freeze tape casting, double sided freeze casting and field directed freeze casting, are also included.

275 citations


Journal ArticleDOI
TL;DR: In this paper, a review of experiments and simulations that find nucleation behaviour that cannot be described by the classical theory of nucleation is presented. But the authors focus on the first step in crystallization and do not discuss the evolution of the nucleation process.
Abstract: Crystals form via nucleation followed by growth. Often nucleation data are interpreted using the classical theory of nucleation, which is essentially a simple theory for the nucleation of a fluid phase. I characterise this classical theory as making six assumptions; I discuss each assumption in turn. I then review experiments and simulations that find nucleation behaviour that cannot be described by the classical theory. The experiments are on the crystallisation from solution of molecules such as drugs and related molecules, ice and calcium carbonate. The review also covers work on non-classical nucleation in solutions of the protein lysozyme, and work on the fascinating phenomenon of nucleation induced by laser pulses. I hope this review will be of interest to those studying the crystallisation of both molecules and ions from solution. The review aims to advance our understanding of the crucial first step in crystallisation, and to enable researchers studying crystallisation in one system to lea...

213 citations


Journal ArticleDOI
TL;DR: In this article, a review of the oxidation behavior of transition metal diboride ceramics is presented, focusing on the transition to linear mass gain kinetics at temperatures above ∼1100°C.
Abstract: The oxidation behaviour of transition metal diboride ceramics is reviewed with emphasis on the performance of zirconium diboride and hafnium diboride. First, the oxidation behaviour of nominally pure diborides is discussed, focusing on the transition to linear mass gain kinetics at temperatures above ∼1100°C. Next, the use of SiC and other additives that produce silica based scales when oxidised is reviewed. These additives improve oxidation protection due to the formation/stability of the outer layer of borosilicate glass that acts as a barrier to diffusion of oxygen to the substrate. However, elevated temperatures (>1650°C) and/or the combination of aerodynamic flow, high heat flux and reactive atmosphere associated with hypersonic flight destabilises the outer oxide and decreases oxidation protection. Other additives that affect the composition and structure of the crystalline oxide scale without forming an outer glassy layer are a promising approach to improving oxidation behaviour of diboride...

187 citations


Journal ArticleDOI
TL;DR: This report reviews the work that is being developed on the isolation and characterisation of some polysaccharides, proteins, glycosaminoglycans and ceramics from marine raw materials, and reviews the application of the previously mentioned materials on specific biomedical applications, in particular their participation on the development of controlled drug delivery systems and tissue engineering scaffolds.
Abstract: Marine organisms are constituted by materials with a vast range of properties and characteristics that may justify their potential application within the biomedical field. Moreover, assuring the sustainable exploitation of natural marine resources, the valorisation of residues from marine origin, like those obtained from food processing, constitutes a highly interesting platform for development of novel biomaterials, with both economic and environmental benefits. In this perspective, an increasing number of different types of compounds are being isolated from aquatic organisms and transformed into profitable products for health applications, including controlled drug delivery and tissue engineering devices. This report reviews the work that is being developed on the isolation and characterisation of some polysaccharides, proteins, glycosaminoglycans and ceramics from marine raw materials. Emphasis is given to agar, alginates, carrageenans, chitin and chitosan, among other polysaccharides, collagen, glycosaminoglycans such as chondroitin sulphate, heparin and hyaluronic acid, calcium phosphorous compounds and biosilica. Finally, this report ends by reviewing the application of the previously mentioned materials on specific biomedical applications, in particular their participation on the development of controlled drug delivery systems and tissue engineering scaffolds.

174 citations


Journal ArticleDOI
TL;DR: In this article, a review of the nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications is presented. But the main focus of this review is on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems.
Abstract: Rare earth (RE) doped oxyfluoride glass ceramics possess interesting optical properties with applications in telecommunications and optoelectronics, such as solid state lasers, optical amplifiers, etc. These materials combine the transparency and mechanical and chemical resistance of aluminosilicate glasses with the low phonon energy and facile incorporation of RE ions in the fluoride crystals. The incorporation of RE ions in the crystalline phases enhances the laser emission intensity, a major property of these materials. Transparency is achieved when crystal size is in the nanometric scale, usually below 40 nm, which avoids light scattering. A strict control of the nucleation and crystal growth processes is therefore necessary which requires a deep knowledge of the crystallisation mechanisms. The great activity and publications in this field in the last decades merit a review providing a comparative study of the different nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications. This is the objective of this review paper which includes 227 references. A general discussion on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems. In the second section, the principal RE doped glass ceramics are presented. After a general introduction about the luminescence processes, including up- and down-conversion, the behaviour of RE elements in glasses and crystals are discussed. Glass ceramic compositions have been divided as follows: glass ceramics with a glass composition following Wang and Ohwaki’s oxyfluoride glass ceramic, and glass ceramics with different matrix compositions, arranged by crystalline phases. Relevant properties, mainly optical and laser, are described in each system along with the most relevant applications of these materials.

153 citations


Journal ArticleDOI
TL;DR: The use of heavy gauge steel sheets for structural applications often requires a combination of high yield strength and adequate toughness as discussed by the authors, and the most cost effective way to achieve high-yield strength and high ductility in low alloyed steels is through grain refinement.
Abstract: The use of heavy gauge steel sheets for structural applications often requires a combination of high yield strength and adequate toughness. The most cost effective way to achieve high yield strength and high ductility in low alloyed steels is through grain refinement. In industrial practice, such refinement is commonly obtained by thermomechanical controlled processing (TMCP). This approach comprises slab reheating to well defined temperatures, a large amount of hot deformation below the non-recrystallisation temperature Tnr and accelerated cooling. In practice, the Tnr is generally raised by the addition of microalloying elements such as Nb and Ti. As these elements contribute substantially to the alloying costs, optimisation of their use allows for a decrease in production cost. Better understanding of the Tnr assists in tuning the rolling process so that optimum mechanical properties can be produced. One area of importance is to recognise that the concept of the Tnr was originally developed for...

152 citations


Journal ArticleDOI
TL;DR: In this article, the effect of inclusion size on fatigue behavior of high strength steels in the very high cycle fatigue (VHCF) regime (>10(7) - 10(9) cycles is reviewed.
Abstract: The effect of inclusion size on fatigue behaviour of high strength steels in the very high cycle fatigue (VHCF) regime (>10(7) - 10(9) cycles) is reviewed. Internal fatigue fractures of high strength steels in the VHCF regime initiate mostly at non-metallic inclusions. The critical inclusion size below which it is hard to initiate fatigue cracking of high strength steels in the VHCF regime is found to be about half the critical value characteristic of the high cycle fatigue (HCF) regime (about 10(5) - 10(7) cycles). A stepwise or duplex S-N curve is observed in the VHCF regime. The shape and form of the S-N curves are affected by inclusion size and other factors including surface condition, residual stress, environment and loading modes. Fatigue strength and fatigue life for high strength steels have been found to obey inverse power laws with respect to inclusion size D of the form sigma(w)proportional to D-n1 and N-f proportional to D-n2 respectively. For fatigue strength, the exponent n(1) has been reported to be similar to 0.33 in the literature for the HCF regime and, more recently, to fall in the range 0.17-0.19 for the VHCF regime. For fatigue life, the exponent n(2) is reported to be similar to 3 in the HCF regime, and in the range 4.29-8.42 in the VHCF regime. A special area was often observed inside a 'fish eye' mark in the vicinity of a non-metallic inclusion acting as the fracture origin for specimens having a long fatigue life. The major mechanisms of formation for this special area are discussed. To estimate the fatigue strength and fatigue life, it is necessary to know the size of the maximum inclusion in a tested specimen, and to be able to infer this value using data from a small volume of steel. The statistics of extreme value (SEV) method and the generalised Pareto distribution (GPD) method are introduced and compared. Finally, unresolved problems and future work required in studying the VHCF of high strength steels are briefly presented.

131 citations


Journal ArticleDOI
TL;DR: In this paper, the structural, thermal, optical and spectroscopic properties of tellurium oxide (TeO2) glasses for their applications in fiber optic and waveguide devices are investigated.
Abstract: This review focuses on the engineering of the structural, thermal, optical and spectroscopic properties of tellurium oxide (TeO2) glasses for their applications in fibre optic and waveguide devices. Unlike silica optical fibres, tellurium oxide glass fibres and light waveguides support propagation of light beyond ∼2 μm, where silica fibres become opaque. Silica fibres also have limited solubility for rare earth oxides due to silica’s structure, which is where tellurium oxide fibres and light waveguides can offer significant opportunities to engineer novel lasers and amplifiers for integrated optics. In this review, we compare the structural properties of TeO2 based glasses, modified by incorporating alkali, alkaline earth, and other oxide compounds. Based on Raman, UV, visible and infrared spectroscopic data, the structural aspects of tellurite glasses are discussed. The effects of compositional modification on the thermal and viscous flow properties are also compared and related with the resistan...

Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution in dissimilar welds and the factors that contribute to premature failure are discussed, and failure is attributed to the steep micro-structural and mechanical property gradients.
Abstract: Dissimilar metal welds between ferritic and austenitic alloys are used extensively in power plants. Premature failure of such welds can occur below the expected creep life of either base metal. This article reviews microstructural evolution in dissimilar welds and describes factors that contribute to premature failure. The microstructure in the as welded condition consists of a sharp chemical concentration gradient across the fusion line. Martensite forms within this gradient due to high hardenability and rapid cooling rates from welding. Upon aging, carbon diffuses down the chemical potential gradient from the ferritic steel toward the austenitic alloy. This can lead to formation of a soft carbon denuded zone in the ferritic steel, and nucleation and growth of carbides in the austenitic steel that produce high hardness. These differences in microstructure and hardness occur over distances of about 50–100 μm. Failure is attributed to the steep microstructural and mechanical property gradients, the...

Journal ArticleDOI
TL;DR: Several biodegradable and bioresorbable materials, as well as technologies and scaffold designs, will be critically reviewed, illustrating the potential of bio-inspired composites and multicomponent platforms for bone tissue engineering.
Abstract: Biological studies indicate that numerous materials present in living tissues owe their success to an optimal combination of properties and adaptive structures, rather than to extreme properties per se. Through studying natural tissues and by biomimesis, new polymer and composite materials may be designed to emulate the structural and functional responses of bone. These materials must ensure biochemical affinity with host tissue through judicious mixing of specific chemical cues. Also, they must mimic the response under load exhibited by natural bone through complex organisation of material phases, i.e. embedding of collagen fibres in the extracellular substance. Fibre and particulate reinforced polymers are increasingly significant in the development of new biomedical materials, since they can be engineered more accurately than monolithic structures. Meanwhile, design of nanocomposites with specific morphological and chemical signals is emerging as a powerful approach to the mimesis of extracellu...

Journal ArticleDOI
TL;DR: In this paper, the authors focus on dislocation arrangement, grain orientation, grain size and surface roughening and their implications on the very high cycle fatigue (VHCF) behavior for selected virtually defect free alloys.
Abstract: Over the last decade, it has been shown for a number of metals that failure occurs even beyond the classical fatigue limit. High frequency testing techniques make it possible to conduct fatigue tests up to 109 or even 1011 cycles for various alloys, ranging from aluminium to high strength steels. As a consequence, the characterisation of fatigue life and damage mechanisms at N>107 cycles [very high cycle fatigue (VHCF)] has become a major research issue. Fatigue life in this regime is dominated by crack initiation. With the overall strain being in the purely elastic range, microstructural features acting as stress raisers lead to localised and inhomogeneously distributed irreversible deformation. Hence, microstructural discontinuities become the leading features controlling fatigue life at very high numbers of cycles. The present survey will focus on dislocation arrangement, grain orientation, grain size and surface roughening and their implications on the VHCF behaviour for selected virtually defect free...

Journal ArticleDOI
TL;DR: The structure of bone and the cells responsible for maintaining bone are described and the mechanisms that cause bone to adapt to mechanical loading have been investigated.
Abstract: Bone is a remarkable living material that comes in two forms with different porosities and different macrostructure, but with the same highly organised microstructure and nanostructure. As bone accumulates damage, it is removed and replaced. When the mechanical demands on bone increase the bone mass increases, while reductions in the loading leads to the removal of bone, thus bone can be considered a ‘smart material’. The ongoing replacement of old bone tissue by new bone tissue is called remodelling. Bone formation, repair and remodelling is controlled and produced by four types of cell, namely osteoblasts, osteoclasts, osteocytes and bone lining cells. Bone remodelling is regulated by signals to these cells generated by mechanical loading. Exactly how loads are transferred into bone, how the bone cells sense these loads and how the signals are translated into bone formation or removal is unknown. In this review, the structure of bone and the cells responsible for maintaining bone are described. The mechanisms that cause bone to adapt to mechanical loading have been investigated. The methods that have been employed in attempts to determine this mechanism are considered.

Journal ArticleDOI
TL;DR: The discovery of iron-based superconductors in early 2008 stimulated the interest of researchers around the globe, including physicists, chemists and materials scientists leading to publication of more than 4000 papers on this superconductor since then as discussed by the authors.
Abstract: The discovery of iron based superconductors in early 2008 stimulated the interest of researchers around the globe, including physicists, chemists and materials scientists leading to publication of more than 4000 papers on this superconductor since then. Since the major player in the superconductor is iron, which had long been believed to be the worst element suited for the superconductivity, this discovery gave tremendous impact on the superconductivity research. Furthermore, this material has favourable characteristics for practical applications such as a relatively high critical temperature, high upper critical field and high critical current density with low anisotropy. In the last 3 years, many derived superconducting materials have been discovered and several theoretical models for the mechanism of superconductivity have been proposed. In this review, the research topics on iron based superconductors are summarised from the viewpoint of materials science.