Showing papers in "International Materials Reviews in 2009"
TL;DR: A comprehensive body of knowledge has built up with respect to the friction stir welding (FSW) of aluminium alloys since the technique was invented in 1991 is reviewed in this article, including thermal history and metal flow, before discussing how process parameters affect the weld microstructure and the likelihood of entraining defects.
Abstract: The comprehensive body of knowledge that has built up with respect to the friction stir welding (FSW) of aluminium alloys since the technique was invented in 1991 is reviewed The basic principles of FSW are described, including thermal history and metal flow, before discussing how process parameters affect the weld microstructure and the likelihood of entraining defects After introducing the characteristic macroscopic features, the microstructural development and related distribution of hardness are reviewed in some detail for the two classes of wrought aluminium alloy (non-heat-treatable and heat-treatable) Finally, the range of mechanical properties that can be achieved is discussed, including consideration of residual stress, fracture, fatigue and corrosion It is demonstrated that FSW of aluminium is becoming an increasingly mature technology with numerous commercial applications In spite of this, much remains to be learned about the process and opportunities for further research a
956 citations
TL;DR: In this article, the basic difference in atomic bonding between the ionic or covalent bonding of the ceramic, compared to the metallic bond is considered, as well as the mismatch in the coefficient of thermal expansion.
Abstract: Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal The joining of engineering ceramics to metals is not always easy There are two main considerations The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond The second consideration is the mismatch in the coefficient of thermal expansion In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either a
213 citations
TL;DR: Hybrid welding as mentioned in this paper combines the combination of a laser and an electrical arc to overcome problems commonly encountered during either laser or arc welding such as cracking, brittle phase formation and porosity.
Abstract: Hybrid welding, using the combination of a laser and an electrical arc, is designed to overcome problems commonly encountered during either laser or arc welding such as cracking, brittle phase formation and porosity. When placed in close contact with each other, the two heat sources interact in such a way as to produce a single high intensity energy source. This synergistic interaction of the two heat sources has been shown to alleviate problems commonly encountered in each individual welding process. Hybrid welding allows increased gap tolerances, as compared to laser welding, while retaining the high weld speed and penetration necessary for the efficient welding of thicker workpieces. A number of simultaneously occurring physical processes have been identified as contributing to these unique properties obtained during hybrid welding. However, the physical understanding of these interactions is still evolving. This review critically analyses the recent advances in the fundamental understa...
193 citations
TL;DR: In this article, the authors reviewed the asymmetry between solidification and melting in detail, including solute partitioning, solute concentration gradients and solute transport in the involved phases.
Abstract: Melting processes influence the microstructure evolution in metal alloys during casting and heat treatments. Melting is often treated as ‘inverse solidification’, which is only appropriate in a limited number of cases. In the present article, asymmetry between solidification and melting is reviewed in detail. The current state of the thermodynamic description of melting under diffusion control is outlined. Kinetic aspects that break the symmetry between solidification and melting that are discussed are solute partitioning, solute concentration gradients and solute transport in the involved phases. The view on nucleation of liquid and pre-melting phenomena, mostly of pure materials, based on experimental and theoretical work, is given. Emphasis is laid on aspects of melting with technical relevance, i.e. melting of alloys. Particularities of thermally and solutally controlled melting are introduced. Mechanisms that involve both melting and solidification simultaneously are capillary drive...
119 citations
TL;DR: A review on the existing and on the new emerging techniques based on supercritical fluid technology for the preparation of scaffolds and particles for tissue engineering applications is presented in this article, where the basic principles underlying each technique are presented as well as the advantages and disadvantages of each process.
Abstract: Over the past several years, the definition of a scaffold for tissue engineering has changed dramatically, from a material that acts only as an inert structural support for cell attachment to serving as a more complex and dynamic environment for tissue development. This paper is a review on the existing and on the new emerging techniques based on supercritical fluid technology for the preparation of scaffolds and particles for tissue engineering applications. Supercritical fluid technology has already proven to be feasible for many pharmaceutical applications and is now emerging as an alternative to conventional materials’ processing methods for the preparation of three-dimensional structures and injectable particles suitable to be used in regenerative medicine. The basic principles underlying each technique are here presented as well as the advantages and disadvantages of each process. The state of the art is reviewed and the major conclusions of the studies reported in the literature are discussed.
106 citations
TL;DR: In this paper, the process of shock compression in reactive powder mixtures and the associated role of various intrinsic and extrinsic characteristics of reactants in the triggering of ultrafast shock induced chemical reactions are discussed.
Abstract: The shock compression of reactive powder mixtures can yield varied chemical behaviour with occurrence of mechanochemical reactions in the timescale of the high pressure state, or thermochemical reactions in the timescale of temperature equilibration, or simply the creation of dense packed highly reactive state of material. The principal challenge has been to understand the processes that distinguish between mechanochemical (shock induced) and thermochemical (shock assisted) reactions, which has broad implications for the synthesis of novel metastable or non-equilibrium materials, or the design of highly configurable next generation energetic materials. In this paper, the process of shock compression in reactive powder mixtures and the associated role of various intrinsic and extrinsic characteristics of reactants in the triggering of ultrafast shock induced chemical reactions are discussed. Experimental techniques employing time resolved diagnostics and results which identify the occurren...
95 citations
TL;DR: In this article, the development and reliability of new Pb-free solders is crucial for the successful substitution of these materials in the electronics industry, and the developments in all these areas are critically examined in this paper.
Abstract: Electronic packaging is a critical part of products such as computers, cellular phones, automotive components and other electronic devices. The package must be tailored to incorporate as many input/output interconnects as possible, in a limited amount of space. Until recently, most solder balls were made of a eutectic Pb–Sn alloy, because of its low melting point, excellent wetting characteristics and adequate creep and thermal fatigue strength. The potential health hazards associated with the toxicity of lead are significant. Given the widespread use of Pb–Sn solder in the manufacture and assembly of circuit boards, the development and reliability of new Pb-free solders is crucial for the successful substitution of these materials in the electronics industry. Pbfree solder alloys are complex materials with various important microstructural attributes. These include the nanoscale precipitates of Ag3Sn in Sn–Ag–Cu or Sn–Ag alloys, as well as Cu6Sn5 intermetallic formed at the interface between the solder and Cu metallisation. The mechanical behaviour of solder alloys is extremely important because solder joints must retain their mechanical integrity under a myriad of conditions such as creep, thermal fatigue, and mechanical shock and drop resistance. A significant amount of work has been carried out on the monotonic shear, creep and thermal fatigue resistance of these materials. An important new area of research is the mechanical shock and vibration fatigue behaviour of Pb-free solders. The developments in all these areas are critically examined in this paper.
81 citations
TL;DR: In this article, the processes that control the production, transportation and deposition of aerosols and how these parameters affect the atmospheric corrosion of zinc on which the aerosols are made were extracted.
Abstract: This paper reviews the processes that control the production, transportation and deposition of aerosols and examines how these parameters affect the atmospheric corrosion of zinc on which t...
77 citations
TL;DR: In this article, a review of the literature on embrittlement of copper and its alloys is presented, showing how its occurrence can be rationalised in simple terms on the basis of what is known of intergranular creep fracture and dynamic recrystallisation.
Abstract: Copper and its alloys generally display a severe reduction in ductility between roughly 300 and 600 degrees C, a phenomenon variously called 'intermediate temperature embrittlement' or 'ductility trough behaviour'. This review of the phenomenon begins by placing it in the wider context of the high-temperature fracture of metals, showing how its occurrence can be rationalised in simple terms on the basis of what is known of intergranular creep fracture and dynamic recrystallisation. Data in the literature are reviewed to identify main causes and mechanisms for embrittlement, first for pure copper, and then for monophase and multiphase copper alloys. Coverage then turns to the 'grain boundary embrittlement' phenomenon, caused by the intergranular segregation of even minute quantities of alloying additions or impurities, which appears to worsen dramatically the intermediate temperature embrittlement of copper alloys. Finally, metal-induced embrittlement, including in particular liquid metal embrittlement, is presented as a second mechanism leading to an exacerbation of the intermediate temperature embrittlement of copper and its alloys.
65 citations
TL;DR: In this paper, a brief introduction of thermodynamic and kinetic models for predicting weld microstructure evolution is given, and the underlying assumptions of these models, including local equilibrium at the interface and conditions, are highlighted.
Abstract: An ability to predict weld microstructure is critical for introduction of new materials, as well as, optimization of existing materials. Complexity of weld microstructure evolution is related to interaction of phase stability, multicomponent diffusion, steep temperature gradients and morphological instabilities during rapid heating and cooling. In the past two decades, computational thermodynamic and kinetic models have been developed to predict these interactions in wide range of alloys. In the first section, a brief introduction of thermodynamic and kinetic models is given. Models for free energy of solid solution and compound phases, as a function of composition and temperature, are discussed. The underlying assumptions of kinetic models, including local equilibrium at the interface and conditions, are highlighted.In the second section, adoption of these models for predicting weld microstructure evolutions is demonstrated with practical examples from structural alloys. The examples focu...
49 citations
TL;DR: In this article, the authors reviewed the main features, recent breakthroughs and future potentials of both the longitudinal and the perpendicular media from a viewpoint of materials science, focusing on the thermodynamic origin of magnetically induced phase separation of Co-Cr based alloys, which governs media noise and coercivity.
Abstract: The tremendous increase in areal density of hard disk drives is mainly ascribed to harmonic development between magnetic recording media and heads in their scaling, especially allowing a commercial transition from the longitudinal to perpendicular recording system This paper reviews the main features, recent breakthroughs and future potentials of both the longitudinal and the perpendicular media from a viewpoint of materials science Special attention is firstly paid to the ‘trilemma’ problem for the media, ie the compromise among writability, thermal stability and signal to noise ratio (SNR) The evolution of media materials these years are then addressed with emphasis on the thermodynamic origin of magnetically induced phase separation of Co–Cr based alloys, which governs media noise and coercivity, and its applications to the current longitudinal media The materials challenges for media to achieve 500 Gb in 22 and above are further predicted from the viewpoints of thermal stability improvement and microstructure control of media materials, and their engineering issues have been discussed for the current Co–Cr based alloys, potential FePt and CoPt ordered, phase separated Co–W based alloys and magnetic rare earth compounds Finally, the future media approaching 1 Tb in 22 and beyond are addressed with respect to the principles, progress, engineering challenges and future directions
TL;DR: The properties of paper are highly dependent on those of the natural fibres from which the sheet is made and their interaction, as determined by the structure of the sheet, are discussed in this paper.
Abstract: The properties of paper are highly dependent on those of the natural fibres from which the sheet is made and their interaction, as determined by the structure of the sheet. The nature of the stochastic variability in paper structure is influenced by fibre properties and manufacturing process variables. The fundamentals of paper forming processes are introduced and the influence of these on structure is discussed in the context of theoretical models. Key mechanical and optical properties are described and their dependence on structure, as guided by theory, is reviewed. Throughout, the structural dependence of paper properties for satisfactory performance in end use applications is emphasised.
TL;DR: The current state of the art for integration between micro-and nanoscales is reviewed for the specific case of nanowires and nanotubes in this article, where the authors present a review of the state-of-the-art solutions provided for the issue of integration.
Abstract: The current state of solutions provided for the issue of integration between micro- and nanoscales is reviewed for the specific case of nanowires and nanotubes. Such structures serve as field emitters, transistors or laser sources, digits for manipulation and handling, as sensing elements or as agents for the modification of surface properties such as the adhesive strength. However, it is noteworthy that the majority of reported device work remains confined to component level prototype development without the prospect of full scale system integration due to the lack of batch compatible fabrication and processing techniques. On the one hand, nanostructures made by self-assembly do not possess a high level of control on their orientation and numbers, and hence, their interfacing and integration with a microsystem pose difficulties. On the other hand, top-down approaches such as manipulation, serial deposition and high resolution lithographic techniques do not satisfy the needs of large scale...
TL;DR: A comprehensive, critical, and up-to-date review for the proeutectoid cementite transformation in steels is presented in this paper, which provides critical new insight into cementite morphologies in both two and three dimensions.
Abstract: A comprehensive, critical, and up to date review is presented for the proeutectoid cementite transformation in steels. It is believed that many of the new findings, features, and concepts presented here for this classic phase transformation in steels serve as a model which may be more broadly applicable to test against many other phase transformations systems as well. There were a number of early investigations of cementite morphology, and this review considers those early results in light of many newer studies that provide critical new insight into cementite morphologies in both two and three dimensions. A number of different orientation relationships (ORs) between proeutectoid cementite and the austenite matrix from which it forms have been reported in the literature, in some cases leading to confusion, and they are critically evaluated here, as are the habit plane, growth direction, and interfacial structure of various morphologies of proeutectoid cementite. Quantitative experimental a...