Showing papers on "Microstructure published in 1986"

The microstructure of sputter-deposited coatings

Abstract: Microstructure is a critical consideration when polycrystalline or amorphous thin films are used for applications such as microcircuit metallization layers and diffusion barriers. The trend in device fabrication toward lower processing temperatures means that such coatings must often be deposited at substrate temperatures T that are low relative to the coating material melting point Tm. The structure of vapor deposited coatings grown under these conditions consists typically of a columnar growth structure, defined by voided open boundaries, which is superimposed on a microstructure which may be polycrystalline (defined by metallurgical grain boundaries) or amorphous. The voided growth structure is clearly undesirable for most applications. Its occurrence is a fundamental consequence of atomic shadowing acting in concert with the low adatom mobilities that characterize low T/Tm deposition, and its formation can be enhanced by the surface irregularities which are common to microcircuit fabrication. This pap...

An in situ HVEM study of dislocation generation at Al/SiC interfaces in metal matrix composites

Abstract: ANNEALED aluminum/silicon carbide (Al/SiC) composites exhibit a relatively high density of dislocations, which are frequently decorated with fine precipitates, in the Al matrix. This high dislocation density is the major reason for the unexpected strength of these composite materials. The large difference (10:1) between the coefficients of thermal expansion (CTE) of Al and SiC results in sufficient stress to generate dislocations at the Al/SiC interface during cooling. In thisin situ investigation, we observed this dislocation generation process during cooling from annealing temperatures using a High Voltage Electron Microscope (HVEM) equipped with a double tilt heating stage. Two types of bulk annealed composites were examined: one with SiC of discontinuous whisker morphology and one of platelet morphology. In addition, control samples with zero volume percent were examined. Both types of composites showed the generation of dislocations at the Al/SiC interface resulting in densities of at least 1013 m-2. One sample viewed end-on to the whiskers showed only a rearrangement of dislocations, whereas, the same material when sectioned so that the lengths of whiskers were in the plane of the foil, showed the generation of dislocations at the ends of the whiskers on cooling. The control samples did not show the generation of dislocations on cooling except at a few large precipitate particles. The results support the hypothesis that the high dislocation density observed in annealed composite materials is a result of differential thermal contraction of Al and SiC. The SiC particles act as dislocation sources during cooling from annealing temperatures resulting in high dislocation densities which strengthen the material.

Morphology and microstructure in electrochemical deposition of zinc

Abstract: We report an experiment in the Ohmically-limited electrochemical deposition of zinc which explicitly probes the link between microscopic structure and macroscopic morphology in the development of interfacial patterns far from equilibrium. We report a previously unrecognized transition region between diffusion-limited aggregation and dendritic growth; analysis of the microstructure suggests mechanisms for the macroscopic expression of crystalline anisotropy. We also report the discovery of a metastable crystalline form of zinc produced during electrodeposition.

The influence of Fe and Cr on the microstructure of cast Al-Si-Mg alloys

Abstract: The detailed microstructure of cast aluminum alloys based on Al-7 pct Si-0.3 pct Mg (A356) has been investigated as a function of Fe and Cr content and solidification rate. It was found that the coarse β phase (FeSiAl5) platelets, which form during solidification of alloys containing Fe, are replaced by “Chinese script” α(bcc) [(Cr, Fe)4Si4Al13] dendritic particles when Cr is added. Coarse π (FeMg3Si6Al8) phase and fine α(bcc) precipitates were found in all of the investigated alloys. Quantitative metallography showed that the length of β phase platelets and the arm length of α(bcc) dendrites increased with decreasing solidification rate and increased Fe content. The T6 heat treatment resulted in the dissolution of π phase and the uniform fine scale precipitation of β′(Mg2Si) in the aluminum rich phase.

Surface Engineering of Titanium with Nitrogen

Abstract: The possibilities for surface hardening of titanium alloys by alloying with nitrogen are reviewed. Alloying has been carried out in the solid state by plasma nitriding and in the liquid state by laser melting in nitrogen. Microstructure, hardness profiles, and fatigue and wear properties have been examined. Wear resistance was found to be greatly improved by both techniques, although at the expense of a drop in fatigue properties. Case depths of 0.1 mm were produced by plasma nitriding, while 0.5 mm case depths and a maximum hardness of 1400 HV0.1 were achieved by laser alloying.

Tailoring Multiphase and Composite Ceramics

Abstract: Processing and Fabrication of Multiphase Ceramics.- Sintering of Multiphase Ceramics.- The Morphological Stability of Continuous Intergranular Phases.- Role of Shear in the Sintering of Composites.- HIP of Liquid Phase Sintered Ceramic Composites.- Sinterable Yttria-Doped Zirconia Powders Chemically Coprecipitated in Non-Aqueous Medium.- Microstructural and Chemical Aspects of a Strontia Sintering Aid on Mg-PSZ.- Phase Relationships in Y-Si-A1-O-N Ceramics.- The Fabrication of Composite O'-B' Sialon Ceramics.- Ceramic Eutectic Composites.- Nickel Oxide-Based Aligned Eutectics.- Imperfections in the Directionally Solidified Structure of NiO-CaO Eutectic.- CVD-Processing of Ceramic-Ceramic Composite Materials.- CVD Fabrication of In-situ Composites of Non-oxide Ceramics.- Preparation of Boron Nitride/Boron Carbide Ceramics by Pyrolysis of Boric Acid-Glycerin Condensation Product.- Porous and Dense Composites for Sol-Gel.- Non-Equilibrium Surface Conditions and Microstructural Changes Following Pulsed Laser Irradiation and Ion Beam Mixing of Ni Overlayers on Sintered Alpha-SiC.- Structure-Property Relations in Multiphase Ceramics.- Quantitative Microstructural Characterization and Description of Multiphase Ceramics.- Displacive Transformation Mechanisms in Zirconia Ceramics and Other Non-Metals.- On Precipitate Morphology in ZrO2 ?-Al2O3, FeTiO3 Matrices.- Particle Toughening in Partially Stabilized Zirconia Influence of Thermal History.- Fabrication and Properties of Transformation-Toughened Sodium Beta"-Alumina.- Phase Transformation and Toughening in MgO Dispersed with ZrO2.- Effect of Impurities on Microstructure and Mechanical Properties of Si3N4-TiC Composites.- On the Microstructure and Hardness Characteristics of Composite Ceramics for Tool Applications.- Mechanical Properties and Wear Resistance of Silicon Nitride-Titanium Carbide Composites.- The Structure and Properties of Interfaces in Reaction-Bonded Silicon Carbides.- Some Factors Affecting Mechanical and Microstructural Anisotropy in Reaction-Bonded Silicon Carbides.- Microstructure-Mechanical Property Relationships in 94% Alumina Ceramics.- New Low Expansion Magnetic Materials-A Composite Approach.- Multiphase Electroceramics.- Electroceramic Composites.- Finite Element/Difference Modeling of Electroceramics.- Multiphase Interaction for Seeking Exotic Phenomena.- Processing of Heterogeneous Ceramics for Dielectric Applications.- Dielectric and Electrical Properties of BaTiO3 Composites.- Composite Piezoelectric Sensors.- Wave Absorption in Piezoceramic-Polymer Composites.- Structured Macrovoids in Ceramic PZT.- Composite Thermistors.- Grain Resistivity and Conduction in Metal Oxide Varistors.- Influence of Microstructure and Chemistry on the Electrical Characteristic of ZnO Varistors.- Influence of Chemical Composition on the Barrier Height in Zn Varistors.- Polycrystalline H3O+-?/?" Alumina: A Designed Composite for Steam Electrolysis.- Fiber and Whisker Reinforced Composites.- The Development of Fiber Reinforced Glasses and Glass Ceramics.- Interfacial Characterization of Glass and Glass-Ceramic Matrix/Nicalon SiC Fiber Composites.- Fatigue Behavior of Silicon Carbide Fiber Reinforced Lithium-Alumino-Silicate Glass-Ceramics.- Fiber Reinforced Composites Via the Sol/Gel Route.- Fiber-Matrix Interactions in Carbon Fiber/Cement Matrix Composites.- Morphological and Mechanical Characterization of Ceramic Composite Materials.- Toughness Anisotropy of a SiC/SiC Laminar Composite.- Whisker Reinforced Ceramic Composites.- Whisker-Reinforced Zirconia-Toughened Ceramics.- Si3N4-SiC Whisker Composite Material.- Mechanical Properties of SiC Fiber-Reinforced Reaction-Bonded Si3N4 Composites.- Surface Energy as an Indicator of Interfacial Mechanical Response.- High Temperature Multiphase Ceramics.- Prospects for Ultra-High-Temperature Ceramic Composites.- Microstructural Engineering of Ceramics for High-Temperature Application.- Tailoring of the Thermal Transport Properties and Thermal Shock Resistance of Structural Ceramics.- Creep Rupture of Siliconized Silicon Carbide.- High Temperature Mechanical Properties of Siliconized Silicon Carbide Composites.- Contributors.

Mechanical properties of toughened ZrO2-Y2O3 Ceramics

Abstract: Tetragonal zirconia polycrystals were produced from high purity powders containing 1.5 to 5.0 mol% Y/sub 2/O/sub 3/ by cold isostatic pressing and sintering, hot-pressing, and hot isostatic pressing. The mechanical properties and microstructures of these resulting materials were examined, with emphasis on the relation between strength and fracture toughness.

Simulation of Microstructure Development During the Hydration of a Cement Compound

Abstract: A mathematical model which simulates the development of microstructure during the hydration of tricalcium silicate (C3S) is described. It is part of a program to develop a model which will quantitatively connect variables associated with different observable characteristics in cement-based systems, from the time of mixing onwards. The core of the model is a mathematical description of all significant aspects of a selected volume of hydrating material. Output is either a numerical description of some aspect of the system or a graphic representation of the microstructure. The model is versatile and interactive and provides the ability to test the consequences of individual hypotheses in a system which has complex interconnected cause-effect relationships. It has the potential for predicting microstructure and bulk properties resulting from a wide variety of hydration conditions. It might also serve as a prototype for other materials which are formed through reaction bonding of powder compacts, including fired ceramics, chemically bonded ceramics, and products of powder metallurgy.

Mechanical properties and thermal stability of CeO/sub 2/ containing tetragonal zirconia polycrystals

Abstract: The strength and fracture toughness of cerium oxide containing tetragonal zirconia polycrystals (Ce-TZP) were studied. The thermal stability of Ce-TZP was also studied by low temperature thermal cycling and aging tests in air and in hot aqueous solution. Ce-TZP (12 mol% cerium oxide) showed very high fracture toughness and inelastic fracture behavior and was resistant to phase transformation during low temperature aging.

Microstructural development in mild and low-alloy steel weld metals

Abstract: The conditions for acicular ferrite formation and the overall transformation behaviour of mild and low-alloy steel weld metals are discussed in terms of deoxidation and alloying practice, solidification microstructure, and operational conditions. Selected weld metal microstructure and composition data are critically reviewed, and new semi-empirical correlations for predictions of the final mechanical properties of the weldment under various welding conditions are presented. The results of this review provide a systematic basis for future research which is required if a sound theoretical treatment of weld metal microstructure development is to be obtained.

An analysis of the microstructure of rapidly solidified Al-8 wt pct Fe powder

Abstract: Rapidly solidified powders of Al-8 wt pct Fe exhibit four distinct microstructures with increasing particle diameter in the size range of 5 μm to 45 μm: microcellular α-Al; cellular α-Al; a-Al + Al6Fe eutectic; and Al3Fe primary intermetallic structure. Small powder particles (~10 μm or less) undercool significantly prior to solidification and typically exhibit a two-zone microcellular-cellular structure in individual powder particles. In the two-zone microstructure, there is a transition from solidification dominated by internal heat flow during recalescence with high growth rates (microcellular) to solidification dominated by external heat flow and slower growth rates (cellular). The origin of the two-zone microstructure from an initially cellular or dendritic structure is interpreted on the basis of growth controlled primarily by solute redistribution. Larger particles experience little or no initial undercooling prior to solidification and do not exhibit the two-zone structure. The larger particles contain cellular, eutectic, or primary intermetallic structures that are consistent with growth rates controlled by heat extraction through the particle surface (external heat flow).

Microstructure studies of AuNiGe Ohmic contacts to n‐type GaAs

Abstract: Microstructure analysis and contact resistance measurements of alloyed AuNiGe contacts to GaAs were performed to assist in the development of low resistance Ohmic contacts for metal–semiconductor field‐effect transistor (MESFET) devices. The contact metals were prepared by sequential deposition of 100 nm of Au–27 at. % Ge, 35 nm Ni, and 50 nm Au onto sputter‐cleaned GaAs wafers in which conducting channels were formed by Si doping to a level of about 1×1018 cm−3. The contact resistances were determined by the transmission line method. Analysis of the substrate and the film microstructure was carried out by x‐ray diffraction, Auger electron spectroscopy (AES), and x‐ray photoelectron spectroscopy (XPS). A strong correlation between the contact resistance and the film microstructure was observed. Low resistances were observed when NiAs compounds containing Ge were in contact with GaAs and the β‐AuGa phase was concentrated near the top of the contact. High resistances were measured when free Au, the α‐AuGa p...

Erosive wear of polymer surfaces by steel ball blasting

Abstract: The erosion behaviour of a variety of polymeric materials has been studied using steel balls at 57 m sec−1 in an air-blast rig. It is shown that the softer polymers (polyethylene, polypropylene, polybutene-1) exhibit an incubation period prior to stabilizing to a linear erosion rate, here defined as reduction in thickness per testing time. The more brittle polymer, polystyrene, on the other hand, shows no incubation time and possesses the highest erosion rate. Further effects can arise from the morphology of semicrystalline polymers. In particular, it was found that a coarse spherulitic microstructure in polypropylene wears much faster than a fine spherulitic one. A decrease in testing temperature generally increases the wear rate. The individual mechanisms of erosive wear are illustrated by SEM micrographs of the worn surfaces. It is suggested that a “brittleness index” of the form (hardnessH/fracture energyG Ic) is a good indicator for the erosion resistance of polymeric materials.

Effect of microstructure on strength and toughness of heat-treated low alloy structural steels

Abstract: Several low alloy structural steels with different levels of Ni, Cr, and Mo and carbon contents ranging from 0.12 to 0.42 wt pct have been studied to determine the effect of transformation structures on strength and toughness. The strength and toughness were, respectively, evaluated with the yield stress (0.2 pct proof stress) in tensile tests under ambient temperature and ductile-brittle transition temperature (DBTT) in Charpy impact tests. The significant conclusions are as follows: well-defined packets are observed in martensitic and lower bainitic structures, and in this case the packet diameter is the primary microstructural parameter controlling the yield stress and DBTT. The mechanical properties are also improved to a lesser degree with decreasing width of the lath present within the packet. If the steel has an upper bainitic structure, the packet is composed of well-defined blocks, and the block size controls the yield stress and DBTT.

Monte Carlo calculation for structural modifications in ion‐assisted thin film deposition due to thermal spikes

Abstract: The microstructure of an ion‐assisted two‐dimensional film, grown from the vapor phase, is modeled by a computer simulation. The inert gas ions, impinging during the vapor deposition, are assumed to create thermal spikes slightly below the film surface. The modification of the microstructure due to atomic hopping, which is induced by the quickly expanding temperature pulse of the spike, is studied. It is demonstrated that as the ratio of the current densities of ions to vapor is increased, the porous columnar microstructure of the film becomes destroyed. Instead of long cavities between the parallel columns, large elongated closed voids are formed.

Grain growth phenomena in films: A Monte Carlo approach

Abstract: A statistical model of microstructural evolution is developed for the evolution of grain structure during deposition. In cases where the atomic mobility on the surface greatly exceeds that in the bulk of the film, the bulk microstructure may be viewed as static while all of the evolution is controlled by the free surface. This leads naturally to a two‐dimensional model of microstructural evolution. Since the surface is advancing at a constant rate during deposition there is a linear relationship between time in the two‐dimensional model and depth in the film. A Monte Carlo computer simulation technique is described which models the evolution of microstructure in this way. Various driving forces are included. Simulated microstructures in the plane of the film and in the plane perpendicular to the free surface are shown.

Method for diffusion bonding of alloys having low solubility oxides

Abstract: Diffusion bonding of surface layers of an alloy, such as an aluminum alloy, having surface oxides of low solubility in the alloy includes treating the surface layers to be bonded to remove existing surface oxide coatings, and diffusion bonding the surface layers to one another by placing the alloy to be bonded under sufficient pressure to cause disruption of the oxide coatings by localized surface deformation of the alloy, enhanced by a superplastic microstructure, without substantial deformation of the alloy, i.e., macroscopic deformation approaching zero percent, while heating the alloy in a non-oxidizing atmosphere for a time sufficient for diffusion bonding to occur. The alloy may be treated so that at least the surface layers thereof have a fine grain structure of the type associated with superplastic forming properties. Components may be formed by diffusion bonding and superplastic forming.

Alloy Microstructures in Cast Metal Matrix Composites

Abstract: This article provides some insight into an area that has here-to-fore been ignored, namely, the matrix microstructure of cast metal matrix composites (MMC). Using the Al-4.5% Cu alloy as a model matrix alloy, the factors influencing the cast microstructure are explored on samples reinforced with several types of fibers. The nature of the fibers, their diameter and distribution along with conventional solidification parameters have a profound influence on the matrix microstructure. A full exploration of the relationships between properties, microstructures and processing parameters is required for the optimization of this class of materials.

Factors influencing as-deposited strength, microstructure, and toughness of manual metal arc welds suitable for C-Mn steel fabrications

Abstract: Published work relating to the influence of several important elements on the strength, toughness, and microstructure of as-deposited weld metal is reviewed Published data for manual metal arc (MMA) welds has been supplemented by the incorporation of pertinent data for other welding processes The factors affecting the strength of as-deposited weld metal include the influence of alloying (where the effects are larger than can be accounted for by solid solution hardening alone) and of grain size Beginning in 1976, considerable advances have been made in understanding the key role which oxygen-containing inclusions play in as-deposited weld metal It is now recognized that large inclusions can initiate cleavage fracture, so that a low weld metal oxygen (and inclusion) content is important for high toughness However, it is also recognized that oxygen-containing inclusions can have a strong influence on as-deposited microstructure, and thus on toughness, since they provide nucleation sites for the

Microstructural Development, Microstructural Characterization and Relation to Mechanical Properties of Dense Silicon Nitride

Abstract: Microstructural development during liquid-phase assisted densification of Si3N4 powder compacts is a function of powder properties, type and amount of additives as well as of processing conditions (time, temperature, pressure). Varying these parameters results in—besides different densities and phase compositions—a different mean grain size and especially grain morphology of the β-grains. These characteristics mainly determine the mechanical properties at temperatures >1000°C. In order to optimize dense Si3N4 materials by correlating microstructural characteristics with mechanical properties, quantitative analysis of the grain structure is necessary. Thus, a method has been developed to quantify microstructures consisting of elongated, rod-like β-grains. By means of these characteristics it is possible to discuss the interdependence between starting composition, processing conditions, microstructure and resulting mechanical properties of dense Si3N4 materials. This leads to a model for the microstructural development during liquid- phase assisted sintering of Si3N4 and the relation between microstructural characteristics and mechanical properties.

The structure and properties of a nickel-base superalloy produced by osprey atomization-deposition

Abstract: The production of a nickel-base superalloy, Rene* 80, by the Osprey atomization-deposition process has been investigated. Dense (>99 pct) material with a fine-grained equiaxed microstructure was deposited using either argon or nitrogen as the atomizing gas. Defects present in the material included a chill region at the collector plate interface, entrapped recirculated particles, porosity, and ceramic particles from the melting and dispensing system. In contrast to other rapid solidification techniques, low oxygen pick-ups are noted in the current technique. Tensile strengths above those displayed by castings are found in both nitrogen and argon atomized material, and in both the as-deposited and heat treated conditions. In addition, no profound mid-temperature ductility loss is displayed by this low oxygen material, in contrast to results on other rapidly solidified material with high oxygen contents. These results are explained in terms of oxygen embrittlement. In view of the excellent properties measured, the attractive economics of the process, and the fact that fine control of the gas/metal flow ratio is shown to be unnecessary, it is concluded that atomization-deposition presents an attractive potential production route for advanced alloys.

The use of new PHACOMP in understanding the solidification microstructure of nickel base alloy weld metal

Abstract: The weld metal microstructures of five commercial nickel base alloys (HASTELLOYS* C-4, C-22, and C-276, and INCONELS* 625 and 718) have been examined by electron probe microanalysis and analytical electron microscopy. It has been found that solidification terminates in many of these alloys with the formation of a constituent containing a topologically-close-packed (TCP) intermetallic phase(i.e., σ, P, Laves). Electron microprobe examination of gas-tungsten-arc welds revealed a solidification segregation pattern of Ni depletion and solute enrichment in interdendritic volumes. New PHACOMP calculations performed on these segregation profiles revealed a pattern of increasingM d (metal-d levels) in traversing from a dendrite core to an adjacent interdendritic volume. In alloys forming a terminal solidification TCP constituent, the calculatedM d values in interdendritic regions were greater than the criticalM d values for formation ofσ as stated by Morinagaet al. Implications of the correlation between TCP phase formation andM d in the prediction of weld metal solidification microstructure, prediction of potential hot-cracking behavior, and applications in future alloy design endeavors are discussed.