Search Results for slowest-diffusing elements

Homogenization heat treatment can be useful for improving the performance and life of an alloy while in service or for improving the processability during fabrication and hot working. This article describes the identification of incipient melt point, slowest-diffusing elements, and microstructural scale for homogenization of metal alloys. It also discusses the CALPHAD software to optimize the homogenization heat treatment and the Scheil module of the commercial thermodynamic modeling software.

This article provides information on the heat-source model, conduction heat-transfer model of parts and fixtures, and the radiation heat-transfer and convection heat-transfer models in a furnace. It describes the two types of furnaces used for heat treating: batch furnaces and continuous furnaces. The heating methods, such as direct-fired heating, radiant-tube heating, and electrical heating, are also discussed. Furnace temperature control is essential to ensure quality heat treatment. The article explains the operating procedure of the automatic temperature controllers used in most furnace operations. Heating simulations can be validated by comparison with measured results in full-scale furnaces. The article also presents several case studies to illustrate the use of the simulations.

When metal is exposed to an oxidizing gas at elevated temperature, corrosion can occur by direct reaction with the gas, without the need for the presence of a liquid electrolyte. This type of corrosion is referred to as high-temperature gaseous corrosion. This article describes the various forms of high-temperature gaseous corrosion, namely, high-temperature oxidation, sulfidation, carburization, corrosion by hydrogen, and hot corrosion.

Cast nickel-base alloys are used extensively in corrosive-media and high-temperature applications. This article briefly reviews the common types of heat treatments of nickel alloy castings: homogenization, stress relieving, in-process annealing, full annealing, solution annealing, quenching, coating diffusion, and precipitation. It describes the three general strengthening mechanisms, namely, solid-solution hardening, age hardening, and carbide precipitation. The article summarizes the typical heat treatment of the general families of nickel-base castings used in industrial applications. It focuses on the solution treatment and age hardening of cast nickel-base superalloys and the heat treatment of cast solid-solution alloys for corrosion-resisting applications. The article also discusses the typical types of atmospheres used in annealing or solution treating: exothermic, endothermic, dry hydrogen, dry argon, and vacuum.

This article discusses the three different modeling approaches for grain structures formed during solidification of metallic alloys: direct modeling of dendritic structure, direct modeling of grain structure, and indirect modeling of grain structure. The main construction bases, the scale at which it applies, and the mathematical background are presented for each modeling approach. The article concludes with a table that presents a comparison of the main inputs/outputs, approximations, numerical methods, kinetics laws, and applications for the three approaches to modeling of dendritic grain solidification.

This article discusses the various methods for evaluating the quench sensitivity of aluminum alloys, namely, time-temperature-property diagrams, the quench factor analysis, the Jominy end-quench method, and continuous-cooling precipitation diagrams. It briefly describes the procedures, applications, advantages, and limitations of these methods.

Alloys intended for use in high-temperature environments rely on the formation of a continuous, compact, slow-growing oxide layer for oxidation, and hot corrosion resistance. This article focuses on the issues related to high-temperature oxidation of superalloys used in gas turbine engine applications. It discusses the general methodologies used to evaluate oxidation resistance of materials. The article describes the performance characteristics of superalloys, single-crystal superalloys, and other high-temperature materials such as refractory metals and ceramics. It discusses hot corrosion of superalloys and airfoil degradation due to deposits resulting from ingested particles or sand. The article concludes with a discussion on the limitations of testing techniques and life prediction.

Analytical transmission electron microscopy (ATEM) is unique among materials characterization techniques as it enables essentially the simultaneous examination of microstructural features through high-resolution imaging and the acquisition of chemical and crystallographic information from small regions of the specimen. This article illustrates the effectiveness of the technique in solving materials problems. The first section of the article provides information on analytical electron microscope (AEM) and its basic operational characteristics as well as on electron optics, electron beam/specimen interactions and the generation of a signal, signal detectors, electron diffraction, imaging, x-ray microanalysis, electron energy loss spectroscopy, and sample preparation. The second section consists of 12 examples, each illustrating a specific type of materials problem that can be solved, at least in part, with AEM.

Hot isostatic pressing (HIP) is used to eliminate porosity in castings. This article provides a history and an overview of the HIP system. It illustrates the reasons for using HIP and discusses the criteria for selecting HIP process parameters. The main mechanisms by which pores are eliminated during HIP are reviewed. The article describes the effect of HIP on the mechanical properties, shape, and structure of castings as well as the effect of inclusions on as-HIPed properties. It examines the problems encountered in HIP and their solution. The article concludes with information on the economics of HIP processing.

Hardening and depth of hardening of steel is a critically important material and process design parameter. This article presents a selective overview of experimental and predictive procedures to determine steel hardenability. It also covers the breadth of steel hardenability, ranging from shallow, to very difficult to harden, to air-hardening steels.

This article provides a detailed discussion on the heat treatment processes for titanium and titanium alloys. These processes are age hardening, solution treatment, aging, and annealing. The article illustrates the characteristics of equilibrium phase diagrams that are important for understanding the heat treatment of titanium alloys. It explains the types of metastable phases encountered in titanium alloys. The article also provides information on the equilibrium phase relationships and properties of titanium alloys.

The formation of defects within additive-manufactured (AM) components is a major concern for critical structural and cyclic load applications. Thus, understanding the mechanisms of defect formation in fusion-based processes is important for prescribing the appropriate process parameters specific to the alloy system and selected processing technique. This article discusses the formation of defects within metal additive manufacturing, namely fusion-based processes and solid-state/sintering processes. Defects observed in fusion-based processes include lack of fusion, keyhole collapse, gas porosity, solidification cracking, solid-state cracking, and surface-connected porosity. The types of defects in solid-state/sintering processes are sintering porosity and improper binder burnout. The article also discusses defect-mitigation strategies, such as postprocess machining, surface treatment, and postprocessing HIP to eliminate defects detrimental to properties from the as-built condition. The use of noncontact thermal, optical, and ultrasound techniques for inspecting AM components are also considered. The final section summarizes the knowledge gap in our understanding of the defects observed within AM components.

This article provides a discussion on the analytical modeling and simulation of residual stress states developed in steel parts and the reasons for these varied final stress states. It illustrates how the metallurgical phase transformation of steel alloys can be applied in the simulation of induction hardening processes and the role of these phase transformations in affecting stress and distortion. Emphasis is placed on induction surface hardening, which is the main application of induction heating in steel heat treatment. The article concludes with examples of induction surface-hardened shafts and through-hardened shafts made of plain carbon steel, alloy steel, and limited hardenability steel.

This article examines the understanding of persistent material changes produced in stainless alloys during light water reactor (LWR) irradiation based on the fundamentals of radiation damage and existing experimental measurements. It summarizes the overall trends and correlations for irradiation-assisted stress-corrosion cracking. The article addresses the effects of various radiation factors on corrosion. These include radiation-induced segregation at grain boundaries, radiation hardening, mode of deformation, radiation creep relaxation, and radiolysis. The article discusses a variety of approaches for mitigating stress-corrosion cracking in LWRs, in categories of water chemistry, operating guidelines, new alloys, design issues, and stress mitigation. It concludes with a discussion on the irradiation effects of irradiation on corrosion of zirconium alloys in LWR environments.

Submerged arc welding (SAW) is suited for applications involving long, continuous welds. This article describes the operating principle, application, advantages, limitations, power source, equipment, and fluxes in SAW. It reviews three different types of electrodes manufactured for SAW: solid, cored, and strip. The article highlights the factors to be considered for controlling the welding process, including fit-up of work, travel speed, and flux depth. It also evaluates the defects that occur in SAW: lack of fusion, slag entrapment, solidification cracking, and hydrogen cracking. Finally, the article provides information on the safety measures to be followed in this process.

This article discusses the mechanics of chip formation and reviews the analytical modeling of the chip formation process by high-speed machining within the framework of continuum mechanics. It examines the relationship between the various high-speed machining parameters. The article describes the cutting tool systems for aluminum alloys, steel, superalloys, and titanium alloys and provides an overview of the alternative cutting tool geometries for increasing tool life. It highlights the factors considered by companies planning to employ high-speed machining systems and concludes with information on the applications of high-speed machining.

This article presents an outline of the physical metallurgical principles that are associated with heat treating of steels. It describes the iron-carbon phase diagram and various types of transformation diagrams, including isothermal transformation diagrams, continuous heating transformation diagrams, and continuous cooling transformation diagrams. The primary design criteria for heat treating of steels this article covers are the minimization of distortion and undesirable residual stresses. The article presents the theoretical and empirical guidelines to understand sources of common heat-treating defects and how they can be controlled. It also presents an example to demonstrate how thermal and transformation-induced strains cause dimensional changes and residual stresses.

This article describes the general categories and metallurgy of heat treatable aluminum alloys. It briefly reviews the key impurities and each of the principal alloying elements in aluminum alloys, namely, copper, magnesium, manganese, silicon, zinc, iron, lithium, titanium, boron, zirconium, chromium, vanadium, scandium, nickel, tin, and bismuth. The article discusses the secondary phases in aluminum alloys, namely, nonmetallic inclusions, porosity, primary particles, constituent particles, dispersoids, precipitates, grain and dislocation structure, and crystallographic texture. It also discusses the mechanisms used for strengthening aluminum alloys, including solid-solution hardening, grain-size strengthening, work or strain hardening, and precipitation hardening. The process of precipitation hardening involves solution heat treatment, quenching, and subsequent aging of the as-quenched supersaturated solid solution. The article briefly discusses these processes of precipitation hardening. It also reviews precipitation in various alloy systems, including 2xxx, 6xxx, 7xxx, aluminum-lithium, and Al-Mg-Li systems.

This article describes the fundamental concepts of heat treatment simulation, including the physical events and their interactions, the heat treatment simulation software, and the commonly used simulation strategies. It summarizes material data needed for heat treatment simulations and discusses reliable data sources as well as experimental and computational methods for material data acquisition. The article provides information on the process data needed for accurate heat treatment simulation and the methods for their determination. Methods for validating heat treatment simulations are also discussed with an emphasis on the underlying philosophy for the selection and design of validation tests. The article also discusses the applications, capabilities, and limitations of heat treatment simulations via selected industrial case studies for a better understanding of the effect of microstructure, distortion, residual stress, and cracking in gears, shafts, and bearing rings.

This article discusses the basic principles of inductively coupled plasma mass spectrometry (ICP-MS), covering different instruments used for performing ICP-MS analysis. The instruments covered include the sample-introduction system, ICP ion source, mass analyzer, and ion detector. Emphasis is placed on ICP-MS applications in the semiconductor, photovoltaic, materials science, and other electronics and high-technology areas.