Showing papers in "Sadhana-academy Proceedings in Engineering Sciences in 2003"
TL;DR: Aluminum matrix composites (AMCs) refer to the class of light-weight high performance aluminium centric material systems as mentioned in this paper, which can be tailored to the demands of different industrial applications by suitable combinations of matrix, reinforcement and processing route.
Abstract: Aluminium matrix composites (AMCs) refer to the class of light weight high performance aluminium centric material systems. The reinforcement in AMCs could be in the form of continuous/discontinuous fibres, whisker or particulates, in volume fractions ranging from a few percent to 70%. Properties of AMCs can be tailored to the demands of different industrial applications by suitable combinations of matrix, reinforcement and processing route. Presently several grades of AMCs are manufactured by different routes. Three decades of intensive research have provided a wealth of new scientific knowledge on the intrinsic and extrinsic effects of ceramic reinforcement vis-a-vis physical, mechanical, thermo-mechanical and tribological properties of AMCs. In the last few years, AMCs have been utilised in high-tech structural and functional applications including aerospace, defence, automotive, and thermal management areas, as well as in sports and recreation. It is interesting to note that research on particle-reinforced cast AMCs took root in India during the 70’s, attained industrial maturity in the developed world nd is currently in the process of joining the mainstream of materials. This paper presents an overview of AMC material ystems on aspects relating to processing, icrostructure, roperties and applications.
1,009 citations
TL;DR: An overview of laser-assisted forming, joining, machining and surface engineering can be found in this paper, where a review of the relevant literature is presented to highlight the recent advances and open questions.
Abstract: Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition.
420 citations
TL;DR: In this paper, an attempt has been made to review different electroless alloy/composite coatings with respect to bath types and their composition, properties and applications, with emphasis on wear and corrosion properties.
Abstract: Since the inception of electroless coating by Brenner & Riddell in 1946, it has been the subject of research interest and, in the past two decades, emphasis has shifted to the studies of its properties and applications. The co-deposition of paniculate matter or substance within the growing film has led to a new generation of electroless composite coatings, many of which possess excellent wear and corrosion resistance. This valuable process can coat not only electrically conductive materials including graphite but also fabrics, insulators like plastics, rubber etc. The low coating rates with these can provide better reflectivity of plated surfaces and many more applications. Coatings can be tailored for desired properties by selecting the composition of the coating alloy/composite/metallic to suit specific requirements. The market for these coatings is expanding fast as the potential applications are on the rise. In the present article, an attempt has been made to review different electroless alloy/composite coatings with respect to bath types and their composition, properties and applications. Different characterisation studies have been conducted on various electroless nickel-based coatings with emphasis on wear and corrosion properties.
322 citations
TL;DR: In this article, a review of the issues in depth and examines emerging directions for improving the performance of orthopaedic devices is presented, including bulk alloying with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings.
Abstract: Chemical stability, mechanical behaviour and biocompatibility in body fluids and tissues are the basic requirements for successful application of implant materials in bone fractures and replacements. Corrosion is one of the major processes affecting the life and service of orthopaedic devices made of metals and alloys used as implants in the body. Among the metals and alloys known, stainless steels (SS), Co-Cr alloys and titanium and its alloys are the most widely used for the making of biodevices for extended life in human body. Incidences of failure of stainless steel implant devices reveal the occurrence of significant localised corroding viz., pitting and crevice corrosion. Titanium forms a stable TiO2 film which can release titanium particles under wear into the body environment. To reduce corrosion and achieve better biocompatibility, bulk alloying of stainless steels with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings are considered potential methods for improving the performance of orthopaedic devices. This review discusses these issues in depth and examines emerging directions.
300 citations
TL;DR: In this paper, it is shown that the martensitic transformation in these three steels produces high dislocation density that confers significant transient hardening, however, the dislocations density decreases during exposure at service temperatures due to recovery effects and for longterm creep strength the sub-grain structure produced under different conditions is most important.
Abstract: The higher steam temperatures and pressures required to achieve increase in thermal efficiency of fossil fuel-fired power-generation plants necessitate the use of steels with improved creep rupture strength. The 9% chromium steels developed during the last three decades are of great interest in such applications. In this report, the development of steels P91, P92 and E911 is described. It is shown that the martensitic transformation in these three steels produces high dislocation density that confers significant transient hardening. However, the dislocation density decreases during exposure at service temperatures due to recovery effects and for long-term creep strength the sub-grain structure produced under different conditions is most important. The changes in the microstructure mean that great care is needed in the extrapolation of experimental data to obtain design values. Only data from tests with rupture times above 3,000 h provide reasonable extrapolated values. It is further shown that for the 9% chromium steels, oxidation resistance in steam is not sufficiently high for their use as thin-walled components at temperatures of 600°C and above. The potential for the development of steels of higher chromium contents (above 11%) to give an improvement in steam oxidation resistance whilst maintaining creep resistance to the 9% chromium steels is discussed.
253 citations
TL;DR: In this paper, the WRC-92 diagram is used as a general guide to maintain a desirable solidification mode during welding, which is a significant problem during the welding of austenitic stainless steels.
Abstract: Solidification cracking is a significant problem during the welding of austenitic stainless steels, particularly in fully austenitic and stabilized compositions. Hot cracking in stainless steel welds is caused by low-melting eutectics containing impurities such as S, P and alloy elements such as Ti, Nb. The WRC-92 diagram can be used as a general guide to maintain a desirable solidification mode during welding. Nitrogen has complex effects on weld-metal microstructure and cracking. In stabilized stainless steels, Ti and Nb react with S, N and C to form low-melting eutectics. Nitrogen picked up during welding significantly enhances cracking, which is reduced by minimizing the ratio of Ti or Nb to that of C and N present. The metallurgical propensity to solidification cracking is determined by elemental segregation, which manifests itself as a brittleness temperature range or BTR, that can be determined using the varestraint test. Total crack length (TCL), used extensively in hot cracking assessment, exhibits greater variability due to extraneous factors as compared to BTR. In austenitic stainless steels, segregation plays an overwhelming role in determining cracking susceptibility.
202 citations
TL;DR: In this paper, a number of special experiments are described in the paper that support the transport of microcracks across the shear plane, and the important role compressive stress plays on the Shear plane.
Abstract: When metal is removed by machining there is substantial increase in the specific energy required with decrease in chip size. It is generally believed this is due to the fact that all metals contain defects (grain boundaries, missing and impurity atoms, etc.), and when the size of the material removed decreases, the probability of encountering a stress-reducing defect decreases. Since the shear stress and strain in metal cutting is unusually high, discontinuous microcracks usually form on the metal-cutting shear plane. If the material being cut is very brittle, or the compressive stress on the shear plane is relatively low, microcracks grow into gross cracks giving rise to discontinuous chip formation. When discontinuous microcracks form on the shear plane they weld and reform as strain proceeds, thus joining the transport of dislocations in accounting for the total slip of the shear plane. In the presence of a contaminant, such as CCI4 vapour at a low cutting speed, the rewelding of microcracks decreases, resulting in decrease in the cutting force required for chip formation. A number of special experiments are described in the paper that support the transport of microcracks across the shear plane, and the important role compressive stress plays on the shear plane. Relatively recently, an alternative explanation for the size effect in cutting was provided based on the premise that shear stress increases with increase in strain rate. When an attempt is made to apply this to metal cutting by Dineshet al (2001) it is assumed in the analysis that the von Mises criterion pertains to the shear plane. This is inconsistent with the experimental findings of Merchant. Until this difficulty is taken care of, together with the promised experimental verification of the strain rate approach, it should be assumed that the strain rate effect may be responsible for some notion of the size effect in metal cutting. However, based on the many experiments discussed here, it is very unlikely that it is totally responsible for the size effect in metal cutting as inferred in Dineshet al (2001).
177 citations
TL;DR: In this article, the effect of stress state on γ/γ′ rafting, kinetics and morphological evolution are discussed with the recent experimental results, and the nature and influence of rafting on creep properties including pre-rafted conditions are discussed.
Abstract: Currently nickel-base single crystal (SX) superalloys are considered for the manufacture of critical components such as turbine blades, vanes etc., for aircraft engines as well as land-based power generation applications. Microstructure and high temperature mechanical properties are the major factors controlling the performance of SX superalloys. Rafting is an important phenomenon in these alloys which occurs during high temperature creep. It is essential to understand the rafting mechanism, and its characteristics on high temperature properties before considering the advanced applications. In this review article, the thermodynamic driving force for rafting with and without stress is explained. The nature and influence of rafting on creep properties including pre-rafted conditions are discussed. In addition, the effect of stress state on γ/γ′ rafting, kinetics and morphological evolution are discussed with the recent experimental results.
141 citations
TL;DR: Carbon-carbon composites rank first among ceramic composite materials with a spectrum of properties and applications in various sectors as discussed by the authors, and are used in a variety of sectors requiring high mechanical properties at elevated temperatures, good frictional properties for brake pads in high speed vehicles or high thermal conductivity for thermal management applications.
Abstract: Carbon-carbon composites rank first among ceramic composite materials with a spectrum of properties and applications in various sectors. These composites are made of fibres in various directions and carbonaceous polymers and hydrocarbons as matrix precursors. Their density and properties depend on the type and volume fraction of reinforcement, matrix precursor used and end heat treatment temperature. Composites made with thermosetting resins as matrix precursors possess low densities (1.55–1.75g/cm3) and well-distributed microporosity whereas those made with pitch as the matrix precursor, after densification exhibit densities of 1.8–2.0g/cm3 with some mesopores, and those made by the CVD technique with hydrocarbon gases, possess intermediate densities and matrices with close porosities. The former (resin-based) composites exhibit high flexural strength, low toughness and low thermal conductivity, whereas the latter (pitch- and CVD-based) can be made with very high thermal conductivity (400–700 W/MK) in the fibre direction. Carbon-carbon composites are used in a variety of sectors requiring high mechanical properties at elevated temperatures, good frictional properties for brake pads in high speed vehicles or high thermal conductivity for thermal management applications. However, for extended life applications, these composites need to be protected against oxidation either through matrix modification with Si, Zr, Hf etc. or by multilayer oxidation protection coatings consisting of SiC, silica, zircon etc.
127 citations
TL;DR: This review summarizes the salient features of clinical applications, where magnetic biomaterials are used, and magnetic intracellular hyperthermia for cancer therapy is discussed in detail.
Abstract: Magnetism plays an important role in different applications of health care. Magnetite (Fe3O4) is biocompatible and therefore is one of the most extensively used biomaterials for different applications ranging from cell separation and drug delivery to hyperthermia. Other than this, a large number of magnetic materials in bulk as well as in the form of nano particles have been exploited for a variety of medical applications. In this review, we summarize the salient features of clinical applications, where magnetic biomaterials are used. Magnetic intracellular hyperthermia for cancer therapy is discussed in detail.
109 citations
TL;DR: A brief overview of the current understanding of the phenomenon of hydrogen damage in steels is presented in this article, where case histories of failures of steel components due to hydrogen embrittlement are briefly discussed.
Abstract: In power plants, several major components such as steam generator tubes, boilers, steam/water pipe lines, water box of condensers and the other auxiliary components like bolts, nuts, screws fasteners and supporting assemblies are commonly fabricated from plain carbon steels, as well as low and high alloy steels. These components often fail catastrophically due to hydrogen embrittlement. A brief overview of our current understanding of the phenomenon of such hydrogen damage in steels is presented in this paper. Case histories of failures of steel components due to hydrogen embrittlement, which are reported in literature, are briefly discussed. A phenomenological assessment of overall process of hydrogen embrittlement and classification of the various damage modes are summarized. Influence of several physical and metallurgical variables on the susceptibility of steels to hydrogen embrittlement, mechanisms of hydrogen embrittlement and current approaches to combat this problem are also presented.
TL;DR: In this paper, a description of the important physical metallurgy aspects of N13Al and NiAl encompassing structure, crystallographic defects, slip systems and phase stability has been presented.
Abstract: A description of the important physical metallurgy aspects of N13Al and NiAl encompassing structure, crystallographic defects, slip systems and phase stability has been presented in this article. The microstructures generated in the two alloys by conventional as well as novel processing techniques have been discussed. The effect of alloying additions on the microstructure has been enumerated. Besides description of the aforementioned physical metallurgy aspects, an important purpose of this review is to focus on the reasons of brittleness in the two alloys and means of alleviating this problem primarily by alloying. The effect of alloying on the slip behaviour has also been described.
TL;DR: In this article, the authors summarise the work pertaining to study of structure and mechanical properties with a view to indicate the directions that have been and can be pursued to overcome property limitations.
Abstract: Aluminium-lithium alloys hold promise of providing a breakthrough response to the crying need for lightweight alloys for use as structurals in aerospace applications. Considerable worldwide research has gone into developing a range of these alloys over the last three decades. As a result, substantial understanding has been developed of the microstructure-based micromechanisms of strengthening, of fatigue and fracture as well as of anisotropy in mechanical properties. However, these alloys have not yet greatly displaced the conventionally used denser Al alloys on account of their poorer ductility, fracture toughness and low cycle fatigue resistance. This review aims to summarise the work pertaining to study of structure and mechanical properties with a view to indicate the directions that have been and can be pursued to overcome property limitations.
TL;DR: In this paper, the structure and stability of nanocrystalline materials is investigated. But the authors focus on the properties of the inter-crystalline regions of the nanometre-sized building blocks.
Abstract: Nanocrystalline materials, which are expected to play a key role in the next generation of human civilization, are assembled with nanometre-sized “building blocks” consisting of the crystalline and large volume fractions of intercrystalline components. In order to predict the unique properties of nanocrystalline materials, which are a combination of the properties of the crystalline and intercrystalline regions, it is essential to understand precisely how the structures of crystalline and intercrystalline regions vary with decrease in crystallite size. In addition, study of the thermal stability of nanocrystalline materials against significant grain growth is both scientific and technological interest. A sharp increase in grain size (to micron levels) during consolidation of nanocrystalline powders to obtain fully dense materials may consequently result in the loss of some unique properties of nanocrystalline materials. Therefore, extensive interest has been generated in exploring the size effects on the structure of crystalline and intercrystalline region of nanocrystalline materials, and the thermal stability of nanocrystalline materials against significant grain growth. The present article is aimed at understanding the structure and stability of nanocrystalline materials.
TL;DR: A broad overview of the present status of the science and technology of bulk metallic glasses and their potential technological uses is presented in this paper, where a detailed study of the structure and the crystallisation behaviour of glasses has enabled the elucidation of the possible atomic configuration in liquid alloys.
Abstract: Bulk glass-forming alloys have emerged over the past fifteen years with attractive properties and technological promise. A number of alloy systems based on lanthanum, magnesium, zirconium, palladium, iron, cobalt and nickel have been discovered. Glass-forming ability depends on various factors like enthalpy of mixing, atomic size and multicomponent alloying. A number of processes is available to synthesise bulk metallic glasses. The crystallisation behaviour and mechanical properties of these alloys pose interesting scientific questions. Upon crystallisation many of these glasses transform to bulk nanocrystals and nanoquasicrystals. A detailed study of the structure and the crystallisation behaviour of glasses has enabled the elucidation of the possible atomic configuration in liquid alloys. Their crystallisation behaviour can be exploited to synthesise novel nanocomposite microstructures and their mechanical properties can be enhanced. A broad overview of the present status of the science and technology of bulk metallic glasses and their potential technological uses is presented.
TL;DR: In this article, the authors provide an account of the rationale for the development of implantable medical devices over the last half-century and explain the criteria that have controlled the selection of biomaterials for these critical applications.
Abstract: This paper provides an account of the rationale for the development of implantable medical devices over the last half-century and explains the criteria that have controlled the selection of biomaterials for these critical applications. In spite of some good successes and excellent materials, there are still serious limitations to the performance of implants today, and the paper explains these limitations and develops this theme in order to describe the recent innovations in tissue engineering, which involves a different approach to reconstruction of the body
TL;DR: The micro-MIM/CIM was developed at Forschungszentram Karlsrahe with the aim of creating a process suitable for a wide range of materials as well as for medium-scale and large-scale production of micro components.
Abstract: Development of micro-MIM/-CIM was started at Forschungszentram Karlsrahe with the aim of creating a process suitable for a wide range of materials as well as for medium-scale and large-scale production of micro components. Using enhanced machine technology and special tempering procedures, this process enables the manufacturing of metal and ceramic devices with smallest wall thicknesses of 50 Μm and structural details of less than 3 Μm. Using ultrafine ceramic powders (e.g. zirconia) and high-quality LIGA mould inserts, surface qualities ofR
a
= 40 nm or Rmax ≤ 3 mm could be obtained. Possible practical applications are demonstrated by components of micro-annular gear pumps made of zirconia for future handling of very small volumes of dangerous fluids and micro samples (tensile and bending specimens) suitable for mechanical testing of metals (316L, 17-4PH) and ceramic materials (A12O3, ZrO2) in the micrometre range.
TL;DR: In this article, various experimental techniques were used to study the transition point from brittle to ductile mode in diamond-turning optical glasses, and the mechanism of the surface generation was discussed.
Abstract: In order to diamond-turn optical glasses to a nanometric surface finish, it is critical to determine the transition point from brittle mode to ductile mode. This paper presents various experimental techniques to study this transition and discusses the mechanism of the surface generation. It has been recognized that tool wear is a serious issue in diamond turning of glasses. Thus, research in future should be concentrated on this field to enable the technology to be applied in commercial production.
TL;DR: A survey on some of the important studies carried out in the recent past on robot control systems developed automatically through evolution due to the interactions between the robot and its environment.
Abstract: In evolutionary robotics, a suitable robot control system is developed automatically through evolution due to the interactions between the robot and its environment It is a complicated task, as the robot and the environment constitute a highly dynamical system Several methods have been tried by various investigators to solve this problem This paper provides a survey on some of these important studies carried out in the recent past
TL;DR: In this article, an extensive database on the isothermal and thermomechanical fatigue behavior of high-temperature titanium alloy EVII 834 and dispersoid-strengthened aluminum alloy X8019 in SiC particle-reinforced as well as unreinv conditions was used to evaluate both the adaptability of fracture mechanics approaches to TMF and the resulting predictive capabilities of determining material life by crack propagation consideration.
Abstract: An existing extensive database on the isothermal and thermomechanical fatigue behaviour of high-temperature titanium alloy EVII 834 and dispersoid-strengthened aluminum alloy X8019 in SiC particle-reinforced as well as unreinv conditions was used to evaluate both the adaptability of fracture mechanics approaches to TMF and the resulting predictive capabilities of determining material life by crack propagation consideration. Selection of the correct microstructural concepts was emphasised and these concepts were, then adjusted by using data from independent experiments in order to avoid any sort of fitting. It is shown that the cyclic /-integral (δJeff concept) is suitable to predict the cyclic lifetime for conditions where the total crack propagation rate is approximately identical to pure fatigue crack growth velocity. In the case that crack propagation is strongly affected by creep, the creep-fatigue damage parameter δCF introduced by Riedel can be successfully applied. If environmental effects are very pronounced, the accelerating influence of corrosion on fatigue crack propagation can no longer implicitly be taken into account in the fatigue crack growth law. Instead, a linear combination of the crack growth rate contributions from plain fatigue (determined in vacuum) and from environmental attack is assumed and found to yield a satisfactory prediction, if the relevant corrosion process is taken into account.
TL;DR: In this paper, the authors investigated cyclic deformation behavior and plasticity-induced martensite formation of metastable austenitic stainless steels at ambient and elevated temperatures, taking into account the influence of the alloying elements titanium and niobium.
Abstract: The aim of the present investigation is to characterise cyclic deformation behaviour and plasticity-induced martensite formation of metastable austenitic stainless steels at ambient and elevated temperatures, taking into account the influence of the alloying elements titanium and niobium. Titanium and niobium are ferrite-stabilising elements which influence the ferrite crystallisation. Furthermore, They form carbides and/or carbonitrides and thus limit the austenite-stabilising effect of carbon and nitrogen. Several specimen batches of titanium and niobium alloyed austenite and of a pure Cr-Ni-steel for comparison were tested under stress and total strain control at a frequency of 5 Hz and triangular load-time waveforms. Stress-strain-hysteresis and temperature measurements were used at ambient temperature to characterise cyclic deformation behaviour. Plasticity-induced martensite content was detected with non-destructive magnetic measuring techniques. The experiments yield characteristic cyclic deformation curves and corresponding magnetic signals according to the actual fatigue state and the amount of martensite. Fatigue behaviour of X6CrNiTil810 (AISI 321), X10CrNiCb189 (AISI 348) and X5CrNi1810 (AISI 304) is characterised by cyclic hardening and softening effects which are strongly influenced by specific loading conditions. Martensite formation varies with the composition, loading conditions, temperature and number of cycles.
TL;DR: In this paper, surface roughness parameters are described and the interaction of light with the surface is discussed, and laser-scattering methods to characterise the surface are detailed, as well as practical cases where such methods have provided useful information about surface characteristics.
Abstract: Surface roughness parameters are described. Various surface characterization techniques are reviewed briefly. Interaction of light with the surface is discussed. Laser-scattering methods to characterise the surface are detailed. Practical cases, where laser-scattering methods have provided useful information about surface characteristics, are illustrated.
TL;DR: The evolution, designs employed, materials being used, and important factors that affect the performance of mechanical heart valves are outlined.
Abstract: Artificial heart valves are engineered devices used for replacing diseased or damaged natural valves of the heart. Most commonly used for replacement are mechanical heart valves and biological valves. This paper briefly outlines the evolution, designs employed, materials being used,. and important factors that affect the performance of mechanical heart valves. The clinical performance of mechanical heart valves is also addressed. Efforts made in India in the development of mechanical heart valves are also discussed.
TL;DR: In this paper, a study of hydrogen-assisted cracking and measurement of diffusible hydrogen content in different Cr-Mo steel welds was conducted and it was shown that under identical conditions, susceptibility to cracking increased with increase in alloy content.
Abstract: Study of hydrogen-assisted cracking and measurement of diffusible hydrogen content in different Cr-Mo steel welds shows that under identical conditions, susceptibility to cracking increased and diffusible hydrogen content decrease with increase in alloy content. Hydrogen permeation studies show that hydrogen diffusivity decreases and solubility increases with increase in alloy content. Thus decrease in diffusible hydrogen content with increase in alloying is attributed to increase in apparent solubility and decrease in apparent diffusivity of hydrogen. Analysis of the results indicates that variation of diffusible hydrogen content and apparent diffusivity of hydrogen with alloy content can be represented as a function of carbon equivalent CE1 originally proposed to predict the hardness in the heat-affected zone of alloy steel welds.
TL;DR: In this paper, a review of the physical and chemical properties of nanocrystalline magnetic systems is presented, both metallic and ceramics, both ferro-and ferrimagnetic systems show superparamagnetic behavior at room temperature.
Abstract: Magnetic properties of materials in their nanocrystalline state have assumed significance in recent years because of their potential applications. A number of techniques have been used to prepare nanocrystalline magnetic phases. Melt spinning, high energy ball milling, sputtering, glassceramization and molecular beam epitaxy are some of the physical methods used so far. Among the chemical methods, sol-gel and co-precipitation routes have been found to be convenient. Ultrafine particles of both ferro- and ferrimagnetic systems show superparamagnetic behaviour at room temperature. Coercivity(Hc) and maximum energy product(BH)max of the magnetic particles can be changed by controlling their sizes. The present paper reviews all these aspects in the case of nanocrystalline magnetic systems — both metallic and ceramics.
TL;DR: In this article, the melting behavior of nanocrystalline interfaces, created by embedding lead and bismuth nanoparticles in quasicrystalline matrices, was studied.
Abstract: Nanomaterials are playing an increasingly important role in modern technologies. Interfaces are crucial in nanotechnology. In this study, we have examined the stability of nanoparticles. Major emphasis is on understanding the effect of interfaces on melting. Melting behaviour of nanocrystalline interfaces, created by embedding lead and bismuth nanoparticles in quasicrystalline matrices, was studied. Sharply faceted and coherent interfaces can be related to sharper melting transitions, while irregularly shaped and incoherent interfaces can be directly correlated with lowering of melting temperatures. It is shown here that solid lead forms a high energy interface with phason strain-free quasicrystal (resulting in a lowering of the melting temperature) while bismuth forms a low energy interface with the quasicrystal (resulting in superheating, unusual for bismuth).
TL;DR: In this paper, the role of vitrification heat treatment on the development of strength between abrasive grains and bonding bridges is examined, and the nature of fracture and wear in vitrified grinding wheels that are used for precision grinding applications.
Abstract: The study of bonding hard materials such as aluminium oxide and cubic boron nitride (cBN) and the nature of interfacial cohesion between these materials and glass is very important from the perspective of high precision grinding. Vitrified grinding wheels are typically used to remove large volumes of metal and to produce components with very high tolerances. It is expected that the same grinding wheel is used for both rough and finish machining operations. Therefore, the grinding wheel, and in particular its bonding system, is expected to react differently to a variety of machining operations. In order to maintain the integrity of the grinding wheel, the bonding system that is used to hold abrasive grains in place reacts differently to forces that are placed on individual bonding bridges. This paper examines the role of vitrification heat treatment on the development of strength between abrasive grains and bonding bridges, and the nature of fracture and wear in vitrified grinding wheels that are used for precision grinding applications.
TL;DR: In this article, the β-stabilizing effect of hydrogen in these materials leading to major changes in the microstructure as a result of hydrogen charging has been investigated and it has been shown that the resulting (extrinsic) effect on the mechanical properties can possibly cover up the direct influence of hydrogen on these materials.
Abstract: Conflicting opinions exist in the literature on the manner in which hydrogen influences the mechanical properties ofβ-titanium alloys. This can be attributed to theβ-stabilizing effect of hydrogen in these materials leading to major changes in the microstructure as a result of hydrogen charging. The resulting (extrinsic) effect of hydrogen on the mechanical properties can possibly cover up the direct (intrinsic) influences.
TL;DR: In this paper, the fundamental characteristics of ELID grinding and their influence on surface finish were investigated. But no proper and detailed studies have been carried out to clarify the fundamental properties for making this process a robust one.
Abstract: Recent developments in grinding have opened up new avenues for finishing of hard and brittle materials with nano-surface finish, high tolerance and accuracy. Grinding with superabrasive wheels is an excellent way to produce ultraprecision surface finish. However, superabrasive diamond grits need higher bonding strength while grinding, which metal-bonded grinding wheels can offer. Truing and dressing of the wheels are major problems and they tend to glaze because of wheel loading. When grinding with superabrasive wheels, wheel loading can be avoided by dressing periodically to obtain continuous grinding. Electrolytic inprocess dressing (ELID) is the most suitable process for dressing metal-bonded grinding wheels during the grinding process. Nano-surface finish can be achieved only when chip removal is done at the atomic level. Recent developments of ductile mode machining of hard and brittle materials show that plastically deformed chip removal minimizes the subsurface damage of the workpiece. When chip deformation takes place in the ductile regime, a defect-free nano-surface is possible and it completely eliminates the polishing process. ELID is one of the processes used for atomic level metal removal and nano-surface finish. However, no proper and detailed studies have been carried out to clarify the fundamental characteristics for making this process a robust one. Consequently, an attempt has been made in this study to understand the fundamental characteristics of ELID grinding and their influence on surface finish.
TL;DR: In this article, the fracture resistance of SA333, Grade 6 steel, under monotonic and cyclic tearing loading has been documented and an attempt has also been made to understand the mechanism responsible for the high fracture toughness of the steel through determination of the effect of constraint on the fracture behaviour and fractographic observations.
Abstract: Design of primary heat transport (PHT) piping of pressurised heavy water reactors (PHWR) has to ensure implementation of leak-before-break concepts. In order to be able to do so, the ductile fracture characteristics of PHT piping material have to be quantified. In this paper, the fracture resistance of SA333, Grade 6 steel — the material used for Indian PHWR — under monotonic and cyclic tearing loading has been documented. An attempt has also been made to understand the mechanism responsible for the high fracture toughness of the steel through determination of the effect of constraint on the fracture behaviour and fractographic observations. FromJ-R tests over a range of temperatures, it was observed that SA333 steel exhibits embrittlement tendencies in the service temperature regime. The fracture resistance of the steel is inferior in the longitudinal direction with respect to the pipe geometry as compared to that in the circumferential direction. Imposition of cyclic unloading during ductile fracture tests for simulation of response to seismic activities results in a dramatic decrease of fracture resistance. It appears, from the observations of effects of constraint on fracture toughness and fractographic examinations, that fracture resistance of the steel is derived partly from the inability of voids to initiate and grow due to a loss of constraint in the crack-tip stress field.