Search Results for interatomic bonds

This chapter explains how the principles of chemical thermodynamics are used in the construction and interpretation of phase diagrams. After a brief review of the laws of thermodynamics, it describes the concept of Gibbs free energy and its application to transformations that occur in single-component and binary solid solutions. It then examines the relationship between the free energy of a solution and the chemical potentials of the individual components. It also explains how to account for the heat of mixing using quasi-chemical models, discusses the effect of interatomic bond energies and chemical potentials, and shows how the equilibrium state of an alloy can be obtained from free-energy curves.

This chapter familiarizes readers with the basic theory of molecular dynamics and its application in the study of materials. It explains how material properties and behaviors are determined through the iterative calculation of motion equations for a collection of atoms under a given set of conditions. It also provides a walk-through on the use of LAMMPS, an open-source molecular dynamics simulator, discussing the selections and inputs of relevance to practical materials problems.

The appendix contains detailed simulation examples through which readers learn how to format and analyze problems using the LAMMPS molecular dynamics simulator. By means of simulation, readers will determine the thermal expansion coefficient of copper, generate stress-strain plots for aluminum at different temperatures, calculate the surface energy of copper for different crystal orientations, investigate diffusion effects in BCC iron, estimate the sliding friction between graphene layers, compare the stacking fault energy of silver and aluminum, and analyze the properties and behaviors of liquids and gases. All examples employ a systematic problem-solving approach and include necessary input code.

Many scientific-technological advances depend critically on solid-state elastic properties, their magnitudes, and their responses to variables like stress and temperature. This chapter provides the definitions and descriptions of elastic constants and emphasizes five aspects of engineering-material solid-state elastic constants: general properties; interrelationships; relationships, especially thermodynamic to other physical properties; changes during cooling from ambient to near-zero temperature; and near-zero-temperature behavior.

Joining comprises a large number of processes used to assemble individual parts into a larger, more complex component or assembly. The selection of an appropriate design to join parts is based on several considerations related to both the product and the joining process. Many product design departments now improve the ease with which products are assembled by using design for assembly (DFA) techniques, which seek to ensure ease of assembly by developing designs that are easy to assemble. This chapter discusses the general guidelines for DFA and concurrent engineering rules before examining the various joining processes, namely fusion welding, solid-state welding, brazing, soldering, mechanical fastening, and adhesive bonding. In addition, it provides information on several design considerations related to the joining process and selection of the appropriate process for joining.

This appendix provides a detailed overview of the crystal structure of metals. It describes primary bonding mechanisms, space lattices and crystal systems, unit cell parameters, slip systems, and crystallographic planes and directions as well as plastic deformation mechanisms, crystalline imperfections, and the formation of surface or planar defects. It also discusses the use of X-ray diffraction for determining crystal structure.

This chapter introduces many of the key concepts on which metallurgy is based. It begins with an overview of the atomic nature of matter and the forces that link atoms together in crystal lattice structures. It discusses the types of imperfections (or defects) that occur in the crystal structure of metals and their role in mechanical deformation, annealing, precipitation, and diffusion. It describes the concept of solid solutions and the effect of temperature on solubility and phase transformations. The chapter also discusses the formation of solidification structures, the use of equilibrium phase diagrams, the role of enthalpy and Gibb’s free energy in chemical reactions, and a method for determining phase compositions along the solidus and liquidus lines.

This chapter discusses the composition, properties, and uses of crystalline ceramics, glasses, clay, and concrete mixes. It also discusses the carbon structure of diamond, graphite, fullerenes, and nanotubes.

Soldering and brazing represent one of several types of methods for joining solid materials. These methods may be classified as mechanical fastening, adhesive bonding, soldering and brazing, welding, and solid-state joining. This chapter summarizes the principal characteristics of these joining methods. It presents a comparison between solders and brazes. Further details on pressure welding and diffusion bonding are also provided. Key parameters of soldering are discussed, including surface energy and surface tension, wetting and contact angle, fluid flow, filler spreading characteristics, surface roughness of components, dissolution of parent materials and intermetallic growth, significance of the joint gap, and the strength of metals. The chapter also examines the principal aspects related to the design and application of soldering processes.

Brazing and soldering jointly represent one of several methods for joining solid materials. This chapter summarizes the principal characteristics of the various joining methods. It then discusses key parameters of brazing including surface energy and tension, wetting and contact angle, fluid flow, filler spreading characteristics, surface roughness of components, dissolution of parent materials, new phase formations, significance of the joint gap, and the strength of metals. The chapter also describes issues in processing aspects that must be considered when designing a joint, and the health, safety, and environmental aspects of brazing.

In a perfect crystalline structure, there is an orderly repetition of the lattice in every direction in space. Real crystals contain a considerable number of imperfections, or defects, that affect their physical, chemical, mechanical, and electronic properties. Defects play an important role in processes such as deformation, annealing, precipitation, diffusion, and sintering. All defects and imperfections can be conveniently classified under four main divisions: point defects, line defects, planar defects, and volume defects. This chapter provides a detailed discussion on the causes, nature, and impact of these defects in metals. It also describes the mechanisms that cause plastic deformation in metals.

Solid-state welding processes are those that produce coalescence of the faying surfaces at temperatures below the melting point of the base metals being joined without the addition of brazing or solder filler metal. This chapter discusses solid-state welding processes such as diffusion welding, forge welding, roll welding, coextrusion welding, cold welding, friction welding, friction stir welding, explosion welding, and ultrasonic welding.

This chapter describes the processes involved in the fabrication of wrought and cast metal products. It discusses deformation processes including bending and forming, material removal processes such as milling, cutting, and grinding, and joining methods including welding, soldering, and brazing. It also discusses powder consolidation, rolling, drawing and extrusion, and common forging methods.

This chapter covers the different types of wear encountered in metalworking processes. It discusses the mechanisms involved in adhesive, abrasive, chemical, and fatigue wear and key contributing factors, including the composition and structure of tool and workpiece materials, the characteristics of contact surfaces, and loading forces imposed by the process. It describes the nature of metal transfer between tool and workpiece surfaces and the role of lubricants, coatings, and textures. It also discusses the use of wear maps, the effects of adhesion, and material-lubricant interactions.

After the fault-tree, a failure-cause identification method has identified potential failure causes and the failure analysis team has prepared a failure mode assessment and assignment (FMA&A). The team knows specifically what to search for when examining components and subassemblies from the failed system. There are numerous techniques and technologies available for examining and analyzing components and subassemblies, which are categorized as follows: optical approaches, dimensional inspection and related approaches, nondestructive test approaches, mechanical and environmental approaches, and chemical and composition analysis for assessing material characteristics. This chapter is a detailed account of the working principle and the steps involved in these techniques and technologies.