Search Results for solid-state methods

This article characterizes the physical differences between powder metallurgy (PM) and wrought or cast materials, as they apply to joining. It discusses acceptable joining procedures and techniques, including welding and brazing and solid-state methods. Information on the weldability of various PM materials is presented. The article also describes the effects of porosity on several important properties that affect the welding characteristics.

This article describes low-temperature solid-state welding processes in relation to the interlayer fabrication method, welding method, and welding parameters. The interlayer fabrication method is used to produce vacuum coated interlayers, electrodeposited interlayers, and foil interlayers. The article discusses welding methods, including uniaxial compression and hot isostatic pressing. The article provides information on the effect of base-metal surface finish on the tensile strength of joints solid-state welded using silver interlayers in tabular form and addresses the surface cleaning steps of base-metals.

This article describes the fundamental aspects of three nondestructive evaluation (NDE) methods of solid-state welds in terms of operation principles. These methods are radiography, ultrasound, and eddy current methods. The article provides examples of these NDE techniques performed on various types of flaws resulting from solid-state welding processes.

Rheology is defined as the study of the flow and deformation of matter. This article begins with an examination of flow behavior. It describes the geometries and methods employed for rheological testing of polymers in their molten state. It also discusses materials that are predominantly in the solid state and the methods employed for solids testing. Examples of unidirectional and dynamic oscillatory testing are provided for different mechanical behaviors.

This article discusses the mechanical properties of soft-interlayer solid-state welds and the implications of these behaviors to service stress states and environments. It illustrates the microstructure of as-deposited coatings and solid-state-welded interlayers. The article reviews factors that affect the tensile loading of strength of soft-interlayer welds: the interlayer thickness, the interlayer strain, and the interlayer fabrication method. It also provides information on stress-corrosion cracking of interlayers and stress behavior of these interlayers during shear and multiaxial loading.

Soft-interlayer solid-state welds that join stronger base metals have unique mechanical properties that are of fundamental interest and may be of critical importance to designers. This article discusses the mechanical properties of soft-interlayer solid-state welds and the implications of these behaviors to service stress states and environments. It describes the tensile loading of soft-Interlayer welds in terms of the effect of interlayer thickness on stress, interlayer strain, time-dependent failure, effect of base-metal properties, and effect of interlayer fabrication method. The article concludes with a discussion on multiaxial loading.

Sintering is a thermal treatment process in which a powder or a porous material, already formed into the required shape, is converted into a useful article with the requisite microstructure. Sintering can be classified as solid-state, viscous, liquid-phase, and pressure-assisted (or pressure) sintering. This article provides information on the mechanisms and theoretical analysis of sintering and focuses on the types, mechanisms, process and microstructural variables, computer simulation, stages, and fundamentals of densification and grain growth of solid-state sintering and liquid-phase sintering. It describes the models for viscous sintering and the methods used in pressure-assisted sintering, namely, uniaxial hot pressing, hot isostatic pressing, sinter forging, and spark plasma sintering.

A number of nondestructive evaluation (NDE) methods, such as radiography, ultrasound, and eddy current, are available to detect flaws in solid materials. This article describes the fundamental aspects of these NDE methods in terms of operation principles. It presents some examples of the methods performed on various types of flaws resulting from solid-state welding processes.

This article focuses on wet chemical methods that have stood the test of time in laboratories around the world. It begins with a description of the appropriateness of classical wet methods. This is followed by sections on sampling procedures, basic chemical equilibria, and wet analytical chemistry. Mechanical methods and nonoxidizing acids and/or acid mixtures for dissolving solid samples for wet chemical analysis are then reviewed. Qualitative methods that are used to identify materials by wet chemical reaction are also included. The article provides information on various methods for the separation of chemical mixtures and on the types of gravimetry and titrimetry. Strategies for removing inclusions are also included to aid in their compositional understanding. The article also briefly describes the processes involved in chemical surface studies and partitioning of oxidation states. It ends by presenting some examples of the applications of classical wet methods.

Both hot and cold forgings are batch-type processes in which steady-state conditions are never fully achieved and the initial lubricant supply must perform adequately for the duration of the operation. This article discusses methods to measure lubricant effectiveness and wear. It describes the mixed-film lubrication and solid film lubrication in cold forging, as well as solid film lubrication and thick film lubrication in hot forging. The article reviews the factors affecting abrasive wear: die hardness, workpiece temperature, and lubrication and die temperature. It concludes with information on ways to improve resistance to abrasive wear.

The term isomorphous refers to metals that are completely miscible in each other in both the liquid and solid states. This article discusses the construction of simple phase diagrams by using the appropriate points obtained from time-temperature cooling curves. It describes the two methods to determine a phase diagram with equilibrated alloys: the static method and the dynamic method. The article illustrates the construction of phase boundaries according to the Gibbs' phase rule and describes the calculation methods that allow the prediction of the phases present, the chemical compositions of the phases present, and the amounts of phases present. Phase diagrams provide useful information for understanding alloy solidification. The article provides two simple models that can describe the limiting cases of solidification behavior.

The electronic microcircuit industry has placed severe demands on metal suppliers to provide metals of the highest reproducible purity attainable as a result of the constant quest for the true values of physical and chemical properties of metals. This article describes the commonly used methods for ultrapurification of metals produced by electrolytic processes, including fractional crystallization, zone refining, vacuum melting, distillation, chemical vapor deposition, and solid state refining techniques. In addition, it describes the trace element analysis and resistance-ratio test methods used to characterize purity. Tables list the values for resistance ratios of zone-refined metals and their corresponding chemical compositions, and provide an example of the detection of impurities to concentrations in the parts per billion range, utilizing a combination of the glow discharge mass spectroscopy method and Leco combustion methods.

This article provides a review of metallographic procedures and techniques for analyzing the microstructure of fusion welded joints. It discusses sample preparation, the use of backing plates, and common sectioning methods. It identifies the various types of defects that can occur in arc welded metals, organizing them according to the sectioning method by which they are observed. It describes the relationship between weld bead morphology and sectioning direction and its effect on measurement error. The article examines micrographs from stainless steel, aluminum, and titanium alloy joints, highlighting important details such as solidification and solid-state transformation structures and what they reveal about the welding process. Besides arc welding, it also discusses laser and electron beam welding methods, resistance and spot welding, and the welding of dissimilar metals.

The main objective for the study of combined-stress fatigue is to obtain fatigue data for axles and to find the criterion for fatigue limit under combined stress. This article begins with a description of the stress states of combined stress and stress fields near crack tips. It provides an account of the various biaxial and multiaxial fatigue testing methods, specimen geometries, and stress intensity factors important in the study multiaxial fatigue. Widely used test methods are the torsion-rotating bending fatigue test and biaxial and triaxial fatigue tests. Common specimen geometries include rectangular plate specimens, cruciform specimens, compact tension shear specimens, compact shear specimens, mode II crack growth specimen, circumferentially notched cylindrical specimens, tubular specimens containing a slit, and solid cylindrical specimens containing a small hole or initial crack.

Sintering provides the interparticle bonding that generates the attractive forces needed to hold together the otherwise loose ceramic powder mass. It also improves hardness, strength, transparency, toughness, electrical conductivity, thermal expansion, magnetic saturation, corrosion resistance, and other properties. This article discusses the fundamentals of sintering and its effects on pore structures and particle density. It addresses some of the more common sintering methods, including solid-state, liquid-phase, and gas pressure sintering, and presents alternative processes such as reaction sintering and self-propagating, high-temperature synthesis. It also describes several pressure densification methods, including hot isostatic pressing, gas pressure sintering, molten particle deposition, and sol-gel processing. The article concludes with a section on grain growth that discusses the underlying mechanisms and kinetics and the relationship between grain growth and densification.

Friction welding (FRW) is a solid-state welding process in which the heat for welding is produced by the relative motion of the two interfaces being joined. This article provides an outline of the mechanisms of friction heating and discusses the two principal FRW methods: direct-drive welding and inertia-drive welding. It summarizes the similar and dissimilar metals that can be joined by FRW and discusses the metallurgical considerations that govern the properties of the resulting weld.

This article describes two methods based on rolling of sheet. The first is roll welding, where two or more sheets or plates are stacked together and then passed through rolls until sufficient deformation has occurred to produce solid-state welds. The other is laser roll welding, which is a hybrid process based on a thin-melting interface for a lap joint of dissimilar-metal sheets using a roller and one-sided laser heating. The article discusses the types, advantages, and applications of roll welding and laser roll welding. It also provides a detailed discussion on the laser roll welding of dissimilar metals.

Friction welding (FRW) is a solid-state welding process in which the heat for welding is produced by the relative motion of the two interfaces being joined. This article describes two principal FRW methods: direct-drive welding and inertia-drive welding. The direct-drive FRW uses a motor running at constant speed to input energy to the weld. The inertia-drive FRW uses the energy stored in a flywheel to input energy to the weld. The article summarizes some of the metals that have been joined by FRW and discusses the metallurgical considerations that govern the properties of the resulting weld. It also presents a schematic illustration of the effect of welding parameters on the finished weld nugget obtained when similar metals are welded using inertia-drive FRW equipment.

Diffusion is the process by which molecules, atoms, ions, point defects, or other particle types migrate from a region of higher concentration to one of lower concentration. This article focuses on the diffusivity data and modeling of lattice diffusion in solid-state materials, presenting their diffusion equations. It discusses different methods for evaluating the diffusivity of a material, including the measurement of diffusion coefficients, composition profiles, and layer growth widths. The article reviews the various types of direct and indirect diffusion experiments to extract tracer, intrinsic, and chemical diffusivities. It provides information on the applications of single-phase and multiphase diffusion.

The microstructure that develops during the solidification stage of cast iron largely influences the subsequent solid-state transformations and mechanical properties of the cast components. This article provides a brief introduction of methods that can be used for simulating the solidification microstructure of cast iron. Analytical as well as numerical models describing solidification phenomena at both macroscopic and microscopic scales are presented. The article introduces macroscopic transport equations and presents analytical microscopic models for solidification. These models include the dendrite growth models and the cooperative eutectic growth models. The article provides some solutions using numerical models to simulate the kinetics of microstructure formation in cast iron. It concludes with a discussion on cellular automaton (CA) technique that can handle complex topology changes and reproduce most of the solidification microstructure features observed experimentally.