Showing papers on "Alloy published in 1992"

Magnesium Alloys and their Applications

Abstract: Partial Table of Contents: ALLOY DEVELOPMENT. Development of Practical High Temperature Magnesium Casting Alloys (J. King). Creep Resistant Mg Alloy Development (K. Pettersen, et al.). New Magnesium Wrought Alloys (C. Jaschik, et al.). Phase Equilibria, Microstructure and Properties of Novel Mg-Mn- Y Alloys (A. Pisch, et al.). TEXTURE AND MICROSTRUCTURE. Texture Analysis as a Tool for Wrought Magnesium Alloy Development (S. Agnew, et al.). Influence of Texture on Deformation Behaviour of Magnesium Alloy AZ31 (R. Gehrmann, et al.). Magnesium Applications in Aerospace and Electronic Industries (B. Landkof). JOINING. Friction Stir Welding of Lightweight Materials (S. Kallee, et al.). MAGNESIUM MATRIX COMPOSITES. Thermal Fatgue of Magnesium Matrix Composites (F. Chmel?k, et al.). Possibilities of the Heat Treatment of MagnesiumMatrix Composites Reinforced with SiC Particles (K. Braszczynska). MECHANICAL DEVELOPMENT. Mechanical Properties of Extruded Magnesium Alloys (B. Closset). Fatigue Design with Cast Magnesium Alloys (C. Sonsino, et al.). Superplasticity of Magnesium-Based Alloys (U. Draugelates, et al.). APPLICATION. High-Speed-Drilling in AZ91 D Without Lubricoolants (F. Tikal, et al.). Cast Magnesium Alloys for Wide Application (P. Detkov, et al.). CORROSION AND SURFACE TREATMENT. Corrosion Properties of Die Cast AM Alloys (M. Videm, et al.). Corrosion Fatigue and Corrosion Creep of Magnesium Alloys (A. Eliezer, et al.). PROCESSING. Quality Index Charts for Mg-based Casting Alloys (C. C?ceres). Semi Solid Injection Molding of MagnesiumAlloys (A. Dworog, et al.). Hydrostatic Extrusion of Magnesium (K. Savage, et al.). Processing of Cellular Magnesium Alloy (Y. Yamada, et al.). PHYSICAL PROPERTIES. Damping in Magnesium and Magnesium Alloys (W. Riehemann). CREEP BEHAVIOUR. Creep of Mg-Zn-Al-Alloys (M. Vogel, et al.). The Microstructure and Creep of an Extruded Mg-Y-Nd Alloy (R. Azari-Khosroshahi). RECYCLING, MELTING, ENVIRONMENTAL. Remelting and Cleaning of Magnesium Scrap (U. Galovsky & M. K?hlein). SIMULATION. An Approach to Determine Solidification Curves of Commercial Magnesium Alloys (D. Mirkovic, et al.). Indexes.

Microstructural evolution and mechanical properties of a forged gamma titanium aluminide alloy

Abstract: A two-phase gamma titanium aluminide alloy, Ti-47Al-1Cr-1V-2.5Nb (in at.%), was studied under forged and various subsequent heat treatment conditions, to investigate the microstructural evolution and the effect of microstructure on room temperature (RT) tensile properties and fracture toughness behavior. Four classes of microstructure and three types of lamellar formation were identified, and their formation mechanisms were analyzed using various analytical techniques including metallography, electron optics, differential thermal analysis (DTA), and crystallography. It was found that both tensile and toughness behavior were profoundly affected by the microstructural variations.

Growth and strain compensation effects in the ternary Si1-x-yGexCy alloy system

Abstract: Strain compensation is an important aspect of heterostructure engineering. In this letter, we discuss the synthesis of pseudomorphic Si1−yCy and Si1−x−yGexCy alloy layers on a silicon (100) substrate by molecular beam epitaxy using solid sources and the controlled strain compensation that results from the introduction of the ternary system. The introduction of C into substitutional sites in the crystal lattice is kinetically stabilized by low‐temperature growth conditions (400–550 °C) against thermodynamically favored silicon‐carbide phases. The lattice constant in Ge is about 4% larger than in Si, whereas in diamond it is 52% smaller. Consequently, the compressive strain caused by 10.8% Ge in a pseudomorphic Si1−xGex alloy can be compensated by adding about 1% carbon into substitutional lattice sites of the film assuming Vegard’s law of linear change of the lattice constant in the alloy as a function of the composition. Using x‐ray diffraction, we observe a partial strain compensation in Si0.75−yGe0.25Cy...

Thin films of Pd/Ni alloys for detection of high hydrogen concentrations

Abstract: Thin alloy films of Pd and Ni (8%

A thermal model of laser cladding by powder injection

Abstract: A two-dimensional (2-D) finite element model is presented for laser cladding by powder injection. The model simulates the quasi-steady temperature field for the longitudinal section of a clad track. It takes into account the melting of the powder in the liquid pool and the liquid/ gas free surface shape and position, which must conform to the thermal field in order to obtain a self-consistent solution. The results for an idealized problem, where there is almost no melting of the substrate material, demonstrate the linear relationship between the laser power, the processing velocity, and the thickness of the deposited layer. The calculated clad heights agreed well with the experimental values for the conditions where a cobalt-based hard-facing alloy is clad onto mild steel with a linearly focused laser source.

Process for electroless plating tin, lead or tin-lead alloy

Abstract: The invention provides a process for electroless plating tin, lead or tin-lead alloy on copper or copper alloy using an electroless plating bath containing a water soluble tin and/or lead salt, an acid capable of dissolving the salts, and a complexing agent. The tin and/or lead content in the bath is maintained high enough to chemically deposit thick films by replenishing the tin and/or lead salt in proportion to an increase in concentration of copper ion dissolving out in the bath. Also provided is an electroless tin, lead or tin-lead alloy plating process in which a water soluble copper salt is added to a fresh bath.

Oxide scale adhesion and impurity segregation at the scale/metal interface

Abstract: The chemistry at scale/metal interfaces was studied using scanning Auger microscopy after removal of the scale in ultra-high vacuum using an in situ scratching technique. Al2O3 and Cr2O3 scales formed between 900°C and 1100°C on Fe-18 wt.% Cr-5 wt.% Al and on Ni-25 wt.% Cr alloys, respectively, were investigated. The adhesion of these scales was determined qualitatively by way of micro-indentation and scratching on the surface oxide. All of the alumina scales fractured to the same degree to expose the metal surface, regardless of the oxidation temperature. The chromia-forming alloy on the other hand, developed more adherent scales at lower oxidation temperatures. About 20 at.% sulfur was found at the metal surface in all cases, and its presence was not only detected on interfacial voids, but also on areas where the scale was in contact with the alloy at temperature. Results from this study clearly demonstrated that sulfur as an alloying impurity does segregate to the scale/alloy interface. However, for alumina scales and chromia scales, the effect of this segregation on oxide adhesion is noticeably different.

Bainite transformation kinetics Part 1 Modified model

Abstract: An earlier model for the overall transformation kinetics of bainite has been corrected and modified to be consistent with known details of the mechanisms of bainitic nucleation and growth. A comparison with published experimental data shows that the model is capable of accurately representing the development of transformation as a function of alloy chemistry and temperature.MST/1627

Dry sliding wear behaviour of squeeze cast aluminium alloy-silicon carbide composites

Abstract: Squeeze cast Al alloy (BSS: LM11) matrix composites, each containing 10 vol.% of SiC particles or fibres, have been investigated for their resistance to dry wear under varying applied pressures (1–3 MPa) at a sliding spped of 2.68 m s−1 against a rotating EN25 steel disc. Seizure pressure of the composites as well as the base alloy was determined using a pin-on-disc machine. The alloy containing SiC particles showed less wear rate than the one having SiC fibre dispersion. The base alloy showed maximum rate of wear. Dispersoid-matrix interfacial bonding and shape of the dispersoid were found to play an important role in governing the wear rate of the composites. Scanning electron microscopy examinations indicated relatively finer grooves on the wear surfaces prior to seizure, while seizure led to severely damaged surfaces. Similarly, wear debris generated during wear was thin and flaky prior to seizure, while bulky debris particles were observed during seizure. A few iron machining chips were also found in all the cases. The results obtained have been explained on the basis of wear-induced microstructural changes and deformation, leading to work hardening in the subsurface regions and wear debris.

Synthesis of molybdenum disilicide by mechanical alloying

Abstract: Considerable interest and effort are being directed towards developing molybdenum disilicide (MoSi2) alloys with low oxygen content. During alloy synthesis, oxygen combines with Si to form glassy SiO2 precipitates at the MoSi2 grain boundaries, resulting in a degradation of its mechanical properties. We have used mechanical alloying, a high-energy ball-milling process, to synthesize alloy powders of MoSi2, MoSi2-27 mol.% MoSi3, MoSi2-50 mol.% Mo5Si3 and MoSi2-50 mol.% WSi2 starting from elemental powders. The processing of the powders, as well as the loading of the powders in graphite dies, was performed under high-purity argon inside a glovebox. The finer grain and particle size of the mechanically alloyed powders enabled us to hot-press them at 1500 °C, which is 300 °C lower than the temperature currently used for hot-pressing commercial powders. We have been successful in reducing the oxygen content in our alloys to about 310 ppm by weight, as measured by nuclear (d,p) reactions. We report the formation of metastable phases in the mechanically alloyed powders and their characterization by X-ray diffraction and differential thermal analysis. We also report the characterization of the hot-pressed alloys by optical and transmission electron microscopy, and the measurement of high-temperature mechanical properties.

Development of alloy electrocatalysts for phosphoric acid fuel cells (PAFC)

Abstract: One of the great scientific achievements for electrocatalysis in the past ten years has been the ability to reproducibly form microparticles of platinum metals in conductive supports. The dimensions of these crystallites are such that up to 50% of the atom content is at the crystallite surface the are single crystals, and have metallurgical properties that are unlike, bulk metals. These have found application as electrocatalysts in hot phosphoric acid fuel cells (PAFC) for oxygen reduction and hydrogen oxidation. Much of the recent work has been involved with developing various binary and ternary alloy combinations while at the same time, maintaining the crystallite microdimensions. Pt−Co−Cr alloys are one of the most favoured combinations for oxygen reduction and the Pt−Pd alloys are favoured for hydrogen oxidation, especially in the presence of trace, poisons such as carbon monoxide and hydrogen sulphide. Operation of these electrocatalysts is the subject of much investigation, with the present conclusion that the apparent mode of catalytic enhancement with the binary and ternary platinum alloys for oxygen reduction, resides in the leaching of the non-platinum elements from the alloy crystallite surfaces to give a microroughening, and thereby an increased reaction surface area.

XPS study of passive films formed on molybdenum‐implanted austenitic stainless steels

Abstract: Austenitic stainless steels (Fe-19Cr-10Ni (at.%)) have been implanted with molybdenum ions (Mo + , 100 keV, 2.5×10 16 atoms cm -2 ). The implanted material has been characterized by XPS and RBS. The implanted region has a thickness of ∼ 1000 A with a maximum molybdenum concentration of ∼ 9 at.% Mo located at ∼210 A from the surface. The effects of implanted molybdenum on the passivation of the alloy in 0.5 M H 2 SO 4 have been investigated by electrochemistry and XPS

Heat treatable sputter-coated glass systems

Abstract: A heat treatable sputter-coated layer system for glass substrates may be applied before heat treatment if the layer system includes a metallic layer of nickel or a high nickel content alloy covered by a separate layer of metallic silicon or an oxide of nickel or the high nickel content alloy, which in turn is covered by a protective metal oxide such as stoichiometric Sn 02.

Ordering and disordering in alloys

Abstract: Content.- I.- Mechanisms and kinetics in ordering and disordering.- Magnetic properties of disordered Ll2-Ni3Al+Fe.- Kinetic disordering of intermetallic compounds through first- and second-order transitions by rapid solidification.- Kinetic states of order in highly nonequilibrium materials.- Resistivity variations during ordering and disordering.- Calorimetric study of reordering of disordered Ll2,Ni3Al based alloys.- Order parameter and lattice parameter of Ll2 ordered alloys, with special reference to Ni3Al-based alloys.- Ordering kinetics in superalloy type intermetallic compounds in relation with diffusion mechanisms.- Phase transformation and order-disorder in Al-Li observed by high resolution microscopy.- Structural instabilities associated with phase transitions and an electron microscopy study.- Electron microscopy investigation of wetting phenomena in Ll2 alloys.- Long-range ordering kinetics in Ni3Al-based alloys with various ordering energies.- Equilibrium and kinetics of thermal ordering or disordering in Ni3Al.- Investigation of deformation induced disorder and re-ordering by subsequent annealing in Ni3Al+B.- Disordering by plastic deformation of short-range and long-range ordered Ni-based alloys.- Defect recombination phenomena in melt-spun ordered alloys of the Fe-Al system.- Ordering and disordering in CuPt-alloys.- Stochastic description of ordering in driven compounds.- Thermodynamical properties of antiphases in fcc ordered alloys.- CVM treatment of order-disorder transformations.- A Monte Carlo study of the antiphase free energy in fcc ordering transitions.- Interface stability in driven compounds.- Monte Carlo study of the phase stability of ordered fcc phases under irradiation.- LMTO/CVM calculations of partial BCC based phase relations in the system Ni-Al-Ti.- Statistical thermodynamics of ordering systems: an improved quasi-chemical approximation.- Martensitic phase transition in systems with frozen atomic order.- An isothermal calorimetric study of the ordering process in quenched ?-Cu-Zn-Al alloy.- II.- Mechanisms of radiation induced amorphization.- Electron-irradiation-induced crystalline-to-amorphous transition in metallic and non-metallic compounds.- Disordering and amorphization of Zr3Al by 3.8 MeV Zi3+ion bombardment.- Disordering induced by very high energy heavy oins in metallic compounds.- Stability of crystals against melting and vitrification.- On the amorphisation of NiGe alloys by mechanical alloying.- Prediction of metastable alloy formation and phase transformations induced by ion bombardment in binary metal systems.- Investigation of order-disorder in non-crystalline binaries using diffraction methods.- Direct imaging using scanning tunnelling microscopy of the atomic structure in amorphous CO1-xPx.- Computer simulation of glass formation in two dimensional networks.- Crystallization and structural transformations in CoZr2 studied by hydrogen-induced internal friction.- Energetics and statistics of order in alloys with application to oxide superconductors.- Characterization of the mechanical disordering process in the Y-Ba-Cu-O system.- Grain growth and gold tracer diffusion in thin films of nanocrystalline Fe and Fe95Zr5.- Moessbauer study of mechanically alloyed powders.- Mechanical alloying of immiscible elements.- Amorphization induced by ball-milling in some pure elements: Si, Ge.- The effect of concentration gradients on the stability of amorphous layers of ternary alloys.- Thermodynamic aspects of amorphization and deformation in Cu-Ti-TiH2 mixtures.- On the energy transfer mechanism in the ball milling powder processing.- Moessbauer study of Fe-B and (Fe, Co, Ni)-B ultra-fine amorphous powders prepared by chemical reduction.- Temperature dependence of the law of approach to magnetic saturation in nonocrystalline ferromagnets.- Electronic origin of stability of quasicrystals.- Quasicrystals and the concept of interpenetration in m35-approximant crystals with long-range icosahedral atomic clustering.- Application of magic strains to predict new ordered phases: a five-fold coordinated crystal structure for silicon.- Index of contributors.

Synthesis of Si1−yCy alloys by molecular beam epitaxy

Abstract: We have synthesized pseudomorphic Si1−yCy (y≤0.05) alloys and strained layer superlattices on silicon by molecular beam epitaxy using solid sources for carbon and silicon. The introduction of C into substitutional sites in the silicon lattice is kinetically stabilized by low‐temperature growth conditions (500–600 °C) and relatively high Si fluxes, against extremely low C solubility (10−6 at 1420 °C) and the thermodynamically favored silicon carbide phases. Higher temperature growth leads to an islanded morphology. At lower temperatures, disruption of epitaxy occurs via the formation of highly twinned layers or even amorphous growth. The temperature window for alloy growth is reduced as the C concentration is increased. X‐ray diffraction, transmission electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy confirm the growth of pseudomorphic, tetragonally strained alloy layers with no detectable silicon carbide precipitation. These alloy layers allow for the engineering of Si‐based lat...

Electrochemical Impedance Spectra and Deterioration Mechanism of Metal Hydride Electrodes

Abstract: Electrochemical impedance spectrum of a metal hydride electrode was interpreted by an equivalent circuit including a reaction resistance on the alloy surface, a contact resistance between the current collector and the pellet, one related to alloy particle‐to‐particle contact, and a Warburg impedance. According to the interpretation, deterioration of a metal hydride electrode using copper‐coated alloy powder was found to be caused by passivation of the alloy surface only. On the other hand, deterioration of an electrode using uncoated alloy was dominated by increase of the contact resistances.

High-temperature oxidation resistance of sputtered micro-grain superalloy K38G

Abstract: The oxidation of sputtered and cast superalloy K38G specimens was studied. The sputtered alloy was microcrystalline, with an average grain size <0.1 μm. The mass gains of the sputtered alloy were much less than those of the cast alloy at 800, 900, and 1000°C up to 500 hr, and were even less than those of pack aluminide on the cast alloy. K38G is a chromia-forming cast nickel-base superalloy, so the oxide scale formed on it is composed of Cr2O3, TiO2, Al2O3, and a spinel. The oxide scale formed on the sputtered alloy was Al2O3. This scale is thin, compact, and adherent. This result implied that micro crystallization reduced the critical aluminum content necessary to form alumina on the surface of this superalloy. No oxide spoliation, as typically observed for cast of aluminized alloys, occurred on the sputtered superalloy. The reduction of the critical aluminum content for the formation of alumina and the improvement of the spoliation resistance may be attributed to the microcrystalline structure formed during sputtering. The numerous grain boundaries favor outward aluminum grain-boundary diffusion, provide increased nucleation sites, and reduced stresses in the oxide scales.