Search Results for line defects

This article defines crystallographic terms and concepts, including crystal structure, unit cell, structure symbols, lattice, space-group notation, and atom position. It schematically illustrates the atom positions, prototypes, structure symbols, space-group notations, and lattice parameters for some of the simple metallic crystals. A table that lists the crystal structures of various metal elements is presented. The crystal structures are described by the Pearson symbols for crystal system, space lattice, total number of atoms per unit cell, and prototype structure. The article tabulates the assorted structure types of metallurgical interest arranged according to Pearson symbol. It also provides information on crystal defects, explaining some significant ones, such as point defects, line defects, stacking faults, and twins.

This article describes crystallographic terms and concepts and illustrates various crystal structures. The crystallographic terms described include crystal structure, unit cell, crystal system, lattice, structure symbols, space-group notation, structure prototype, atom positions, point groups, and equivalent positions. The article presents a table of assorted structure types of metallurgical interest arranged according to the Pearson symbol. It also schematically illustrates atom positions, prototypes, structure symbols, space-group notations, and lattice parameters for some of the simple metallic crystals. The article concludes with a description of some of the most significant crystal defects such as point defects, line defects, and stacking faults.

Crystal structure is the arrangement of atoms or molecules in the solid state that involves consideration of defects, or abnormalities, in idealized atomic/molecular arrangements. The three-dimensional aggregation of unit cells in the crystal forms a space lattice or Bravais lattice. This article provides a brief review of the terms and basic concepts associated with crystal structures. It also discusses some of the significant defects obstructing plastic flow in real crystals, namely point defects, line defects, stacking faults, twins, and cold work. Several tables in the article provide information on the crystal structures and lattice parameters of allotropes of metallic elements.

Materials are selected and used as a result of a match between their properties and the needs dictated by the intended application. This article provides information on how the composition and structure determine the properties of materials. It describes common structural elements that are most important in materials. The article presents a historical perspective of the use of materials and illustrates the evolution of engineering materials.

Plastic deformation can occur in metals from various mechanisms, such as slip, twinning, diffusion creep, grain-boundary sliding, grain rotation, and deformation-induced phase transformations. This article emphasizes on the mechanism of slip and twinning under cold working conditions. It discusses the factors on which the structures developed during plastic deformation depend. These factors include crystal structure, amount of deformation, composition, deformation mode, and deformation temperature and rate. The article illustrates the microstructural features that appear after substantial deformation when revealed through metallographic investigation.

Additive manufacturing produces a change in the shape of a substrate by adding material progressively. This article discusses the simulation of laser deposition and three principal thermomechanical phenomena during the laser deposition process: absorption of laser radiation; heat conduction, convection, and phase change; and elastic-plastic deformation. It provides a description of four sets of data used for modeling and simulation of additive manufacturing processes, namely, material constitutive data, solid model, initial and boundary conditions, and laser deposition process parameters. The article considers three aspects of simulation of additive manufacturing: simulation for initial selection of process parameter setup, simulation for in situ process control, and simulation for ex situ process optimization. It also presents some examples of computational mechanics solutions for automating various components of additive manufacturing simulation.

The corrosion behavior of a metal or alloy is determined by its composition and structural features, the environment and stresses to which it is exposed, and the behavior of any corrosion products generated. This article provides a detailed discussion on the fundamentals of pure metals, impure metals, and alloys. It highlights the ways in which the metallurgical variables, namely, composition and structure, influence the corrosion properties of metals and alloys in aqueous environment.

This article reviews the concepts considered important for an understanding of the processes used for preparing cobalt-chromium alloy implants, the microstructures resulting from this processing, and the resulting material properties. The review includes solidification of alloys, diffusionless (martensitic) phase transformation as occurs with face-centered cubic to hexagonal close-packed transformation in cobalt-chromium alloys, and stacking faults and twins and their role in this transformation. It also discusses the strengthening mechanisms that are responsible for the mechanical properties of cast and wrought cobalt alloys. The article contains tables that list the commonly used cobalt alloys and their biomedical applications and chemical compositions. It discusses the mechanical and corrosion properties of cobalt alloys, and provides a description of the microstructure of cobalt alloys.

Coatings, such as those applied to ships, must be resistant to abrasion, in the case of cargo hold coatings, and cyclic changes of chemicals and tank cleaning, in the case of tank linings. Failures and defects can manifest themselves at various times in the life of a coating. To determine the cause and mechanism of coating failure, all possible contributory factors must be evaluated together with a detailed history from the time of application to the time the failure was first noted. Many coating failures require further evaluation and analysis to be carried out by a qualified chemist or coating specialist, often using specialized laboratory equipment. The article presents examples of coating failures and defects, together with descriptions, probable causes, and suggested preventative measures.

The crucible induction furnace is growing as an alternative melting unit to the cupola furnace due to its low specific power and reduced power consumption during solid melting material. This article details the process engineering features of the crucible induction furnace. It discusses the various processes involved in melting, holding, and pouring of liquid melt in crucible induction furnaces wherein the holding operation is carried out in channel furnace and pouring operation in pressure-actuated pouring furnaces. The article examines the behavior of furnace refractory lining to defects such as erosion, infiltration, crack formation, and clogging, and the corresponding preventive measures to avoid the occurrence of these defects. It elucidates the overall furnace operations, including commissioning, operational procedures, automatic process monitoring, inductor change, and dealing with disturbances.

X-ray topography is the general term for a family of x-ray diffraction imaging techniques capable of providing information on the nature and distribution of imperfections. This article provides a detailed account of x-ray topography techniques, providing information on the historical background and development trends in x-ray diffraction topography. The discussion covers the general principles, components of systems, and applications of x-ray topography techniques, namely conventional X-ray topographic techniques and synchrotron x-ray topographic techniques.

This article provides information on the general structural features and origins of metals. The characteristic structural features of single-phase metals and alloys, such as grain structure and substructure, are discussed. The article also describes the major types of multiphase structures and macrostructure of metals and alloys.

This article discusses the concepts of quality control (QC) and quality assurance (QA), and clarifies the differences and similarities in the roles and responsibilities of QC and QA personnel. It describes the inspection procedures used to verify proper surface preparation and installation of the protective coating/lining system. Prior to beginning surface-preparation operations, many specifications will require a presurface-preparation inspection to verify the correction of fabrication defects and removal of surface contamination such as grease, oil, cutting compounds, lubricants, and chemical contaminants. When inspecting concrete prior to coating installation, three areas of concern exist: surface roughness, moisture content in concrete, and acidity/alkalinity of the surface. The article provides information on the industry standards for assessing surface cleanliness. It details postcoating application quality requirements, including measuring of dry-film thickness, assessing intercoat cleanliness, verifying minimum and maximum recoat intervals, performing holiday/pinhole detection, conducting cure/hardness testing, and assessing adhesion of the applied coating system.