Showing papers on "Microstructure published in 1995"

The Science and Engineering of Thermal Spray Coatings

Abstract: Preface to the Second Edition. Preface to the First Edition. Acronyms, Abbreviations and Symbols. 1 Materials Used for Spraying. 1.1 Methods of Powders Production. 1.1.1 Atomization. 1.1.2 Sintering or Fusion. 1.1.3 Spray Drying (Agglomeration). 1.1.4 Cladding. 1.1.5 Mechanical Alloying (Mechanofusion). 1.1.6 Self-propagating High-temperature Synthesis (SHS). 1.1.7 Other Methods. 1.2 Methods of Powders Characterization. 1.2.1 Grain Size. 1.2.2 Chemical and Phase Composition. 1.2.3 Internal and External Morphology. 1.2.4 High-temperature Behaviour. 1.2.5 Apparent Density and Flowability. 1.3 Feeding, Transport and Injection of Powders. 1.3.1 Powder Feeders. 1.3.2 Transport of Powders. 1.3.3 Injection of Powders. References. 2 Pre-Spray Treatment. 2.1 Introduction. 2.2 Surface Cleaning. 2.3 Substrate Shaping. 2.4 Surface Activation. 2.5 Masking. References. 3 Thermal Spraying Techniques. 3.1 Introduction. 3.2 Flame Spraying (FS). 3.2.1 History. 3.2.2 Principles. 3.2.3 Process Parameters. 3.2.4 Coating Properties. 3.3 Atmospheric Plasma Spraying (APS). 3.3.1 History. 3.3.2 Principles. 3.3.3 Process Parameters. 3.3.4 Coating Properties. 3.4 Arc Spraying (AS). 3.4.1 Principles. 3.4.2 Process Parameters. 3.4.3 Coating Properties. 3.5 Detonation-Gun Spraying (D-GUN). 3.5.1 History. 3.5.2 Principles. 3.5.3 Process Parameters. 3.5.4 Coating Properties. 3.6 High-Velocity Oxy-Fuel (HVOF) Spraying. 3.6.1 History. 3.6.2 Principles. 3.6.3 Process Parameters. 3.6.4 Coating Properties. 3.7 Vacuum Plasma Spraying (VPS). 3.7.1 History. 3.7.2 Principles. 3.7.3 Process Parameters. 3.7.4 Coating Properties. 3.8 Controlled-Atmosphere Plasma Spraying (CAPS). 3.8.1 History. 3.8.2 Principles. 3.8.3 Process Parameters. 3.8.4 Coating Properties. 3.9 Cold-Gas Spraying Method (CGSM). 3.9.1 History. 3.9.2 Principles. 3.9.3 Process Parameters. 3.9.4 Coating Properties. 3.10 New Developments in Thermal Spray Techniques. References. 4 Post-Spray Treatment. 4.1 Heat Treatment. 4.1.1 Electromagnetic Treatment. 4.1.2 Furnace Treatment. 4.1.3 Hot Isostatic Pressing (HIP). 4.1.4 Combustion Flame Re-melting. 4.2 Impregnation. 4.2.1 Inorganic Sealants. 4.2.2 Organic Sealants. 4.3 Finishing. 4.3.1 Grinding. 4.3.2 Polishing and Lapping. References. 5 Physics and Chemistry of Thermal Spraying. 5.1 Jets and Flames. 5.1.1 Properties of Jets and Flames. 5.2 Momentum Transfer between Jets or Flames and Sprayed Particles. 5.2.1 Theoretical Description. 5.2.2 Experimental Determination of Sprayed Particles' Velocities. 5.2.3 Examples of Experimental Determination of Particles Velocities. 5.3 Heat Transfer between Jets or Flames and Sprayed Particles. 5.3.1 Theoretical Description. 5.3.2 Methods of Particles' Temperature Measurements. 5.4 Chemical Modification at Flight of Sprayed Particles. References. 6 Coating Build-Up. 6.1 Impact of Particles. 6.1.1 Particle Deformation. 6.1.2 Particle Temperature at Impact. 6.1.3 Nucleation, Solidification and Crystal Growth. 6.1.4 Mechanisms of Adhesion. 6.2 Coating Growth. 6.2.1 Mechanism of Coating Growth. 6.2.2 Temperature of Coatings at Spraying. 6.2.3 Generation of Thermal Stresses at Spraying. 6.2.4 Coatings Surfaces. 6.3 Microstructure of the Coatings. 6.3.1 Crystal Phase Composition. 6.3.2 Coatings' Inhomogeneity. 6.3.3 Final Microstructure of Sprayed Coatings. 6.4 Thermally Sprayed Composites. 6.4.1 Classification of Sprayed Composites. 6.4.2 Composite Coating Manufacturing. References. 7 Methods of Coatings' Characterization. 7.1 Methods of Microstructure Characterization. 7.1.1 Methods of Chemical Analysis. 7.1.2 Crystallographic Analyses. 7.1.3 Microstructure Analyses. 7.1.4 Other Applied Methods. 7.2 Mechanical Properties of Coatings. 7.2.1 Adhesion Determination. 7.2.2 Hardness and Microhardness. 7.2.3 Elastic Moduli, Strength and Ductility. 7.2.4 Properties Related to Mechanics of Coating Fracture. 7.2.5 Friction and Wear. 7.2.6 Residual Stresses. 7.3 Physical Properties of Coatings. 7.3.1 Thickness, Porosity and Density. 7.3.2 Thermophysical Properties. 7.3.3 Thermal Shock Resistance. 7.4 Electrical Properties of Coatings. 7.4.1 Electrical Conductivity. 7.4.2 Properties of Dielectrics. 7.4.3 Electron Emission from Surfaces. 7.5 Magnetic Properties of Coatings. 7.6 Chemical Properties of Coatings. 7.6.1 Aqueous Corrosion. 7.6.2 Hot-gas Corrosion. 7.7 Characterization of Coatings' Quality. 7.7.1 Acoustical Methods. 7.7.2 Thermal Methods. References. 8 Properties of Coatings. 8.1 Design of Experiments. 8.2 Mechanical Properties. 8.2.1 Hardness and Microhardness. 8.2.2 Tensile Adhesion Strength. 8.2.3 Elastic Moduli, Strengths and Fracture Toughness. 8.2.4 Friction and Wear. 8.3 Thermophysical Properties. 8.3.1 Thermal Conductivity and Diffusivity. 8.3.2 Specific Heat. 8.3.3 Thermal Expansion. 8.3.4 Emissivity. 8.3.5 Thermal Shock Resistance. 8.4 Electric Properties. 8.4.1 Properties of Conductors. 8.4.2 Properties of Resistors. 8.4.3 Properties of Dielectrics. 8.4.4 Electric Field Emitters. 8.4.5 Properties of Superconductors. 8.5 Magnetic Properties. 8.5.1 Soft Magnets. 8.5.2 Hard Magnets. 8.6 Optical Properties. 8.6.1 Decorative Coatings. 8.6.2 Optically Functional Coatings. 8.7 Corrosion Resistance. 8.7.1 Aqueous Corrosion. 8.7.2 Hot-medium Corrosion. References. 9 Applications of Coatings. 9.1 Aeronautical and Space Industries. 9.1.1 Aero-engines. 9.1.2 Landing-gear Components. 9.1.3 Rocket Thrust-chamber Liners. 9.2 Agroalimentary Industry. 9.3 Automobile Industry. 9.4 Ceramics Industry. 9.4.1 Free-standing Samples. 9.4.2 Brick-Clay Extruders. 9.4.3 Crucibles to Melt Oxide Ceramics. 9.4.4 Ceramic Membranes. 9.5 Chemical Industry. 9.5.1 Photocatalytic Surfaces. 9.5.2 Tools in Petrol Search Installations. 9.5.3 Vessels in Chemical Refineries. 9.5.4 Gas-well Tubing. 9.5.5 Polymeric Coatings on Pipeline Components. 9.5.6 Ozonizer Tubes. 9.6 Civil Engineering. 9.7 Decorative Coatings. 9.8 Electronics Industry. 9.8.1 Heaters. 9.8.2 Sources for Sputtering. 9.8.3 Substrates for Hybrid Microelectronics. 9.8.4 Capacitor Electrodes. 9.8.5 Conductor Paths for Hybrid Electronics. 9.8.6 Microwave Integrated Circuits. 9.9 Energy Generation and Transport. 9.9.1 Solid-oxide Fuel Cell (SOFCs). 9.9.2 Thermopile Devices for Thermoelectric Generators. 9.9.3 Boilers in Power-generation Plants. 9.9.4 Stationary Gas Turbines. 9.9.5 Hydropower Stations. 9.9.6 MHD Generators. 9.10 Iron and Steel Industries. 9.10.1 Continuous Annealing Line (CAL). 9.10.2 Continuous Galvanizing Section. 9.10.3 Stave Cooling Pipes. 9.11 Machine Building Industry. 9.12 Medicine. 9.13 Mining Industry. 9.14 Non-ferrous Metal Industry. 9.14.1 Hot-extrusion Dies. 9.14.2 Protective Coatings against Liquid Copper. 9.14.3 Protective Coatings against Liquid Zirconium. 9.15 Nuclear Industry. 9.15.1 Components of Tokamak Device. 9.15.2 Magnetic-fusion Energy Device. 9.16 Paper Industry. 9.16.1 Dryers. 9.16.2 Gloss Calender Rolls. 9.16.3 Tubing in Boilers. 9.17 Printing and Packaging Industries. 9.17.1 Corona Rolls. 9.17.2 Anilox Rolls. 9.18 Shipbuiding and Naval Industries. 9.18.1 Marine Gas-turbine Engines. 9.18.2 Steam Valve Stems. 9.18.3 Non-skid Helicopter Flight Deck. References. Index.

Ti(C,N) cermets — Metallurgy and properties

Abstract: An overview of the metallurgical reactions during the vacuum sintering process of powder mixtures for the manufacture of cermets is presented. The relatively complex phase reactions in the multi-component system Ti/Mo/W/Ta/Nb/C,N-Co/Ni are discussed. The liquid binder phase reacts with titanium carbonitride by preferentially dissolving titanium carbide leaving titanium nitride undissolved. The compositions and the amounts of the gas species set free during the sintering process were monitored and led —together with differential thermal analysis — to a better understanding of the mechanisms that govern the sintering behaviour. The properties and the microstructure of cermets depend on the nature and the alloy status of the prematerials. The composition of the prematerials with respect to the carbon-nitrogen ratio, the stoichiometry of the hard phase and the amount and composition of the binder phase have a decisive influence on the properties and the cutting performances of the final products. Optimization of the properties with respect to the desired performance is possible. Examples of the cermet cutting performance in various applications are discussed.

Processing, microstructure, and mechanical behavior of cast magnesium metal matrix composites

Abstract: Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. This article presents a liquid mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite, based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding, in the fracture process of the composite.

The Influence of the Microstructure on the Properties of Ferroelectric Ceramics

Abstract: Conventional ferroelectric perovskite type ceramics have dielectric, piezoelectric and elastic properties which depend on grain size and on domain configuration. Very fine grained ceramic is not splitted in domains. This causes strong elastic stress fields in the grains which counteract ferroelectricity. Tetragonal fine grained ceramic has a simple laminar domain structure and high elastic stress fields inside the grain and at the grain boundaries. These stress fields cause very high permittivity. In coarse grained ceramics the stress fields inside the grain are eliminated by a three-dimensional network of domains. In fine and in coarse grained ceramics the domain walls contribute considerably to the dielectric, piezoelectric and elastic constants at frequencies below a relaxation frecuency which is between 200 and 1000 MHz. At low temperatures, however, the domain wall contributions freeze in. Acceptor doping lowers the domain wall contributions and shifts the relaxation frequency to higher values. The properties of the conventional ceramics will be compared wiht properties of thin firms and with properties of relaxor ceramics.

Effects of microstructure on the deformation and fracture of γ-TiAl alloys

Abstract: Deformation and fracture behavior of two-phase γ-TiAl alloys were investigated under monotonic tension loading conditions for duplex and lamellar microstructural forms. The effects of microstructure on tensile properties and deformation-fracture behavior are analyzed for deformation temperatures below and above the brittle-ductile transition. The crack initiation toughness and associated strains near the crack tip are used to explain the inverse relationship between ductility and toughness observed at room temperature. Fracture resistance behavior and toughening mechanisms at room temperature are explained in terms of microstructure and deformation anisotropy. The competition between the effects of grain size and lamellar spacing or tensile and toughness properties is discussed.

Decomposition and primary crystallization in undercooled zr41.2ti13.8cu12.5ni10.0be22.5 melts

Abstract: Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glasses were prepared by cooling the melt with a rate of about 10 K/s and investigated with respect to their chemical and structural homogeneity by atom probe field ion microscopy and transmission electron microscopy. The measurements on these slowly cooled samples reveal that the alloy exhibits phase separation in the undercooled liquid state. Significant composition fluctuations are found in the Be and Zr concentration but not in the Ti, Cu, and Ni concentration. The decomposed microstructure is compared with the microstructure obtained upon primary crystallization, suggesting that the nucleation during primary crystallization of this bulk glass former is triggered by the preceding diffusion controlled decomposition in the undercooled liquid state.

Grain Size Dependence of Hardness in Dense Submicrometer Alumina

Abstract: Pressureless sintered alumina compacts with a submicrometer microstructure exhibit a hardness that approaches or even exceeds the level of advanced hot-pressed composites of Al{sub 2}O{sub 3} + 35 vol% TiC, whereas the strength of both ceramics is approximately the same. The combination of reduced dislocation mobility (due to the small grain size), high density, and density homogeneity are the prerequisites for the surprisingly high hardness. Quasi-conventional powder processing is used to produce these outstanding alumina bodies.

Mechanical properties of the binary titanium-zirconium alloys and their potential for biomedical materials

Abstract: Mechanical properties of titanium-zirconium binary alloys were investigated in order to reveal their possible use for new biomedical materials and to collect useful data for alloy design through a hardness test, a tensile test, and optical microscopy. The hardness of the alloy containing 50% zirconium was approximately 2.5 times as large as the hardness of pure titanium and pure zirconium. Tensile tests showed a similar tendency. No changes between hardness of as cast specimens and as homogenized specimens were observed, nor were changes in microstructures noted. Comparisons between the Ti-6Al-4V alloy and the Ti-Zr-6Al-4V alloy indicated that a titanium-zirconium alloy could provide a base material for a new biomedical alloy. From these results, it was concluded that new alloys for biomedical materials should be designed as titanium-zirconium base alloys. © 1995 John Wiley & Sons, Inc.

High‐Temperature Mechanical Behavior of Stoichiometric Magnesium Spinel

Abstract: The elastic and mechanical behavior, from room temperature up to 1300deg;C, of Stoichiometric polycrystalline magnesium aluminum spinel is studied. Elastic modulus, fracture toughness, and modulus of rupture measurements and observations of polished and fracture surfaces have been performed. Two well-differentiated regions of fracture behavior as a function of temperature have been found. In the low-temperature region, this material behaves elastically, whereas in the high-temperature (>800deg;C) region, plastic phenomena take place.

Morphology, structure, and growth of nanoparticles produced in a carbon arc.

Abstract: The morphology and crystalline microstructure of carbon-encapsulated nanoparticles produced in a Huffman-Kr\"atschmer fullerene reactor are studied systematically as a function of location within the reactor. X-ray powder diffraction and high-resolution transmission electron microscopy are used to characterize powder harvested from the reactor walls and the inner and outer cores of the cathode deposit. We observe increased graphitization and crystallinity, more faceting, and more gaps between the nanoparticle and the encapsulating carbon cages in the cathode deposit when compared to the wall powder. We propose a growth model based on gas-phase nucleation to explain these observations, linking carbon arc nanoparticle synthesis to existing work on gas aggregation cluster sources.

Processing, microstructure, and properties of co-continuous alumina-aluminum composites

Abstract: A novel co-continuous composite of Al 2 O 3 and Al has been developed, consisting of approximately 65% (by volume) of the ceramic phase. It is formed by a liquid phase displacement reaction, involving the displacement of Si from SiO 2 and its replacement by Al. A model for the formation mechanism is presented, based on the reaction thermodynamics and the associated experimentally determined transformation kinetics. It is shown that the process is essentially near-net shape, in which the features of the SiO 2 precursors are faithfully reproduced in the composite product. Various physical and mechanical properties that are exhibited by this composite have been determined and are presented.

The effect of soldering process variables on the microstructure and mechanical properties of eutectic Sn-Ag/Cu solder joints

Abstract: Fundamental understanding of the relationship among process, microstructure, and mechanical properties is essential to solder alloy design, soldering process development, and joint reliability prediction and optimization. This research focused on the process-structure-property relationship in eutectic Sn-Ag/Cu solder joints. As a Pb-free alternative, eutectic Sn-Ag solder offers enhanced mechanical properties, good wettability on Cu and Cu alloys, and the potential for a broader range of application compared to eutectic Sn-Pb solder. The relationship between soldering process parameters (soldering temperature, reflow time, and cooling rate) and joint microstructure was studied systemati-cally. Microhardness, tensile shear strength, and shear creep strength were measured and the relationship between the joint microstructures and mechani-cal properties was determined. Based on these results, low soldering tempera-tures, fast cooling rates, and short reflow times are suggested for producing joints with the best shear strength, ductility, and creep resistance.

Properties of ultra-fine grain binderless cemented carbide ‘RCCFN’

Abstract: Conventional binderless cemented carbide is known as WC-3% TiC-2% TaC cemented carbide with a mean WC grain diameter of about 2 μm, which does not include a binder phase. This alloy, however, has no binder phase and therefore low strength. The authors investigated the effects of mean diameter of raw WC powder on mechanical characteristics, and found that the smaller the mean diameter of raw WC powder, the lower the temperature at which sintering is possible and the higher the hardness and strength becomes. An investigation was also made on the effects of grain growth suppression additives on the alloy using 0.6 μm diameter WC powder, which offers the highest mechanical characteristics, with the objective of enhancing characteristics through finer grains. Hardness increased with additional amounts of Cr 3 C 2 and VC. Strength peaked at a certain additive amount, with superior values of H R A = 95.5 and transverse-rupture strength = 1.8 GPa. The microstructure was found to be composed of only very fine and uniform carbides; a mirror surface of 7 nm Rtm was obtained by mirror polishing. These characteristics make it possible for this alloy to be used in various optical applications.

Al-B-C Phase Development and Effects on Mechanical Properties of B4C/Al-Derived Composites

Abstract: B4C/A1 offers a family of engineering materials in which a range of properties can be developed by postdensiflcation heat treatment. In applications where hardness and high modulus are required, heat treatment above 600°C provides a multiphase ceramic material containing only a small amount of residual metal. Heat treatment between 600° and 700°C produces mainly A1B2; 700° and 900°C results in a mixture of A1B2 and A14BC; 900° and 980°C produces primarily A14BC; and 1000° to 1050°C results in A1B24C4 with small amounts of A14C3 if the heating does not exceed 5 h. Deleterious A14C3 is avoided by processing below 1000°C. All of these phases tend to form large clusters of grains and result in lower strength regardless of which phase forms. Toughness is also reduced; the least determinal phase is A1B2. The highest hardness (88 Rockwell A) and Young's modulus (310 GPa) are obtained in Al4BC-rich samples. AlB2-containing samples exhibit lower hardness and Young's modulus but higher fracture toughness. While the modulus, Poisson's ratio, and hardness of multiphase B4C/A1 composites containing 5–10 vol% free metal are comparable to ceramics, the unique advantage of this family of materials is low density (>2.7 g/cm3) and higher than 7 MPa-m1/2 fracture toughness.

Prevention of groove tip deformation in brightness enhancement film

Abstract: A method of producing a microstructure bearing article (11) that includes the steps of molding the microstructure (22, 24, 26, 28) on the base (34), curing the resin that forms the microstructure, and heat treating the microstructure. The heat treating is performed at a temperataure that is at least equal to a normal glass transition temperature of the resin. The heat treating raises the glass transition temperature of the resulting polymer above approximately 333 ° K such that groove tip impression is reduced. Such articles are useful in backlit displays (10) which are useful in computers and the like.

Ion induced stress generation in arc‐evaporated TiN films

Abstract: The influence of Ti ion bombardment on the intrinsic stress and microstructure of TiN films during deposition by arc evaporation of Ti in pure N2 has been investigated. Ions with an average charge of +1.6 were accelerated from the arc discharge by a negative substrate bias Vs between 5 and 540 V which yielded a steady‐state substrate temperature between 300 and 600 °C, respectively. The compressive intrinsic stresses in the films, as determined by the x‐ray‐diffraction (XRD) sin2 ψ method after subtracting the thermal stress contribution at room temperature, changed abruptly from 1.9 to a maximum of 6.5 GPa as Vs increased from 5 to 100 V. The compressive stress then decreased monotonically to ∼1.6 GPa as Vs increased to 540 V. Broadening of XRD peaks (β) showed accompanying inhomogeneous strain with a maximum values for Vs=100 V. Cross‐sectional transmission electron microscopy showed a dense columnar film microstructure. Electron microdiffraction showed a distorted structure within the same columns for ...

Modelling of texture evolution for materials of hexagonal symmetry—II. application to zirconium and titanium α or near α alloys

Abstract: This work describes the evolution of texture and microstructure during cold rolling of different Ti and Zr alloys. These alloys accommodate deformation with prismatic glide and with “secondary” mechanisms (gliding and/or twinning) which are different according to the type of alloys and may vary with deformation degree. We have modelled texture evolution during cold rolling of two Ti and Zr alloys, using a Taylor theory. The choice or relevance of the model variant (FC = full Constrained, RC = Relax Constrained) are discussed. In order to account for the changes in the secondary systems during deformation, we have decided to work by steps, since there are no defined hardening laws accepted for each system. The results of the modelling, both for the Pole Figures (PF) and for the Orientation Density Function (ODF), agree well with experiment in the range from 0 to 80% reduction. Therefore, a good knowledge of the microstructure evolution and of the deformation mechanisms is required.

Nitriding of austenitic stainless steel by plasma immersion ion implantation

Abstract: Plasma immersion ion implantation (PI3™), in which the diffusion of nitrogen from a low pressure r.f. plasma is combined with the implantation of nitrogen ions at energies up to 45 kV, is an effective means of nitriding austenitic stainless steel. At temperatures up to 450 °C, tribological properties can be improved without loss of corrosion resistance. In common with other nitriding processes in this temperature range, a supersaturated f.c.c. phase is formed, sometimes described as expanded austenite, which is maintained to very high nitrogen concentrations. At higher temperatures, chromium nitride is precipitated and the expanded austenite decomposes, leading to a reduction in corrosion resistance. Glancing-angle X-ray diffraction (XRD) of PI3-treated AISI 316 stainless steel at temperatures between 350 and 450 °C suggests that a highly homogeneous layer of expanded austenite is produced. The expansion increases with increasing process time, but decomposition of the supersaturated phase occurs after several hours of treatment if the temperature is too close to 450 °C. For a fixed process time, the expansion appears to be greatest at the lower temperatures (350 °C), although it can also be influenced by other processing parameters such as plasma density. Microstructural examination by cross-sectional transmission electron microscopy (TEM) has challenged the identification of the supersaturated phase as expanded austenite and reveals the complexity of the modified layer not seen by glancing-angle XRD. Most striking is the formation of a thick (2–3 μm) amorphous zone which may contain nanocrystalline precipitates of CrN and α-ferrite. A highly defective layer (up to 2 μm thick) of expanded austenite has been observed to underlie the amorphous zone where nitrogen diffusion is facilitated by the high defect density. Only partial reconciliation of the TEM results with the XRD observations has been possible to date.

Selected processing for non-equilibrium light alloys and products

Abstract: A new class of light or reactive elements and monophase α′-matrix magnesium- and aluminum-based alloys with superior engineering properties, for the latter being based on a homogeneous solute distribution or a corrosion-resistant and metallic shiny surface withstanding aqueous and saline environments and resulting from the control during synthesis of atomic structure over microstructure to net shape of the final product, said α′-matrix being retained upon conversion into a cast or wrought form. The manufacture of the materials relies on the control of deposition temperature and in-vacuum consolidation during vapor deposition, on maximized heat transfer or casting pressure during all-liquid processing and on controlled friction and shock power during solid state alloying using a mechanical milling technique. The alloy synthesis is followed by extrusion, rolling, forging, drawing and superplastic forming for which the conditions of mechanical working, thermal exposure and time to transfer corresponding metastable α′-matrix phases and microstructure into product form depend on thermal stability and transformation behavior at higher temperatures of said light alloy as well as on the defects inherent to a specific alloy synthesis employed. Alloying additions to the resulting α′-monophase matrix include 0.1 to 40 wt. % metalloids or light rare earth or early transition or simple or heavy rare earth metals or a combination thereof. The eventually more complex light alloys are designed to retain the low density and to improve damage tolerance of corresponding base metals and may include an artificial aging upon thermomechanical processing with or without solid solution heat and quench and annealing treatment for a controlled volume fraction and size of solid state precipitates to reinforce alloy film, layer or bulk and resulting surface qualities. Novel processes are employed to spur production and productivity for the new materials.

Grain Growth and Fracture Toughness of Fine‐Grained Silicon Carbide Ceramics

Abstract: Fine-grained silicon carbide ceramics with an average grain size of 0.11 {micro}m were liquid-phase sintered from fine {beta}-SiC powder by hot pressing. The hot-pressed materials were subsequently annealed to enhance grain growth. The diameters and aspect ratios of grains in the hot-pressed and annealed materials were measured on polished and etched surfaces. The bimodal grain size distribution in annealed materials was obtained at 1,850 C without appreciable phase transformation. The average diameter and average aspect ratio increased with annealing time. The fracture toughness of a fine-grained silicon carbide ceramic determined by the Vickers indentation method was 1.9 MPa {center_dot} m{sup 1/2}. The fracture toughness increased to 6.1 MPa {center_dot} m{sup 1/2} after grain growth by annealing at 1,850 C for 12 h. Higher fracture toughness of annealed materials is due to bridging by elongated grains as evidenced by R-curve-like behavior.

The Effects of Dopants on the Chemistry and Tribology of Sputter-Deposited MoS2 Films

Abstract: The fact. that dopants improve the friction and wear properties of sputtered MoS2 films is well known. However, the role of dopants in the mechanisms governing friction and wear are not well understood. The purpose of this work is to gain a fundamental understanding of their role by co-depositing a number of materials, i.e., Ni, Fe, Au, and. Sb2O3, with MoS2 and evaluating their effects on film chemistry, crystallinity, microstructure, and tribology. Friction and wear measurements were collected, using ball-on-flat and dual-rub shoe tribom-eters. Other physical and chemical properties were obtained using SEM, XPS, XRD) and Raman spectroscopy. Crystalline MoS2 was seen in all of the films. In Sb2O3-doped films, an amorphous phase was also observed. The presence of dopants caused film densification and affected crystallite size. They had little effect on the overall crystallite orientation. In addition, dopants caused a reduction in the mean and. variance of the friction coefficient and an increase in wear ...

Microstructures minimizing the energy of a two phase elastic composite in two space dimensions. II: The vigdergauz microstructure

Abstract: For modeling coherent phase transformations, and for applications to structural optimization, it is of interest to identify microstructures with minimal energy or maximal stiffness. The existence of a particularly simple microstructure with extremal elastic behavior, in the context of two-phase composites made from isotropic components in two space dimensions, has previously been shown. This “Vigdergauz microstructure” consists of a periodic array of appropriately shaped inclusions. We provide an alternative discussion of this microstructure and its properties. Our treatment includes an explicit formula for the shape of the inclusion, and an analysis of various limits. We also discuss the significance of this microstructure (i) for minimizing the maximum stress in a composite, and (ii) as a large volume fraction analog of Michell trusses in the theory of structural optimization.

Ball milling-induced nanocrystal formation in aluminum-based metallic glasses

Abstract: Various experimental techniques have been used to investigate the effect of mechanical milling on the structural stability of rapidly solidified aluminum-based metallic glasses. Using transmission electron microscopy (TEM) and X-ray diffraction methods, the formation of nanocrystalline Al particles in some ball-milled Al-rich metallic glasses (such as Al90Fe5Gd5 and Al90Fe5Ce5) is clearly observed. For other compositions with lower Al concentration such as Al85Ni5Y10, no such phase transformation can be detected by TEM or X-ray. However, differential scanning calorimetry (DSC) measurements show that the crystallization peaks of the ball-milled Al85Ni5Y10 metallic glass shifted to higher temperatures, while the crystallization enthalpy associated with the first exothermic peak decreased to a lower value, revealing that certain structural changes have taken place as a result of mechanical deformation. The compositional dependence of the structural stability of Al-based metallic glasses against mechanical deformation suggests that the nanocrystal formation induced by a deformation process is different from that caused by a thermal process. The large plastic strain induced atomic displacements and the enhancement of atomic mobility during the deformation process, are the possible mechanisms of mechanical deformation-induced crystallization. Our results demonstrate a new way of obtaining nanophase glassy composite alloy powders which are suitable for engineering applications upon further consolidation processing.

Mechanical properties of a partially sintered alumina

Abstract: An experimental investigation was performed to understand the mechanical properties of alumina with moderate amounts of porosity (∼ 20–40%). Young's modulus, strength and fracture toughness showed similar behavior as a function of the degree of sintering. For low sintering temperatures (