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Published: 01 January 2006
Fig. 21 Nabarro-Herring creep results from a higher vacancy concentration in regions of a material experiencing a tensile stress vis-à-vis regions subject to a compressive stress. (a) This results in a vacancy flux from the former to the latter areas, and a mass flux in the opposite direction
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Image
Published: 01 January 2005
Fig. 21 Nabarro-Herring creep results from a higher vacancy concentration in regions of a material experiencing a tensile stress vis-à-vis regions subject to a compressive stress. (a) This results in a vacancy flux from the former to the latter areas, and a mass flux in the opposite direction
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Series: ASM Handbook
Volume: 14A
Publisher: ASM International
Published: 01 January 2005
DOI: 10.31399/asm.hb.v14a.a0004020
EISBN: 978-1-62708-185-6
..., followed by the models of constitutive behavior. It provides a discussion on creep mechanisms involving dislocation and diffusional flow, such as the Nabarro-Herring creep and the Coble creep. The equations for the several creep rates are also presented. Research on the mechanism of the superplastic flow...
Abstract
The constitutive relations for metalworking include elements of behavior at ambient temperature as well as high-temperature response. This article presents equations for strain hardening and strain-rate-sensitive flow, with alternate sections on empirically determined properties, followed by the models of constitutive behavior. It provides a discussion on creep mechanisms involving dislocation and diffusional flow, such as the Nabarro-Herring creep and the Coble creep. The equations for the several creep rates are also presented. Research on the mechanism of the superplastic flow in fine-grain metals has encompassed many ideas, such as the diffusional creep, dislocation creep with diffusional accommodation at grain boundaries, and concepts of grain-mantle deformation. The article concludes with information on the kinetics of superplastic deformation processes, including low stress behavior, concurrent grain growth, and high stress behavior.
Image
Published: 01 December 2009
Fig. 8 Schematic showing the flow of atoms from compressive boundaries to tensile boundaries during diffusional Nabarro-Herring creep. Vacancy flow occurs in the direction opposite to that of the atom flow.
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Series: ASM Handbook
Volume: 14B
Publisher: ASM International
Published: 01 January 2006
DOI: 10.31399/asm.hb.v14b.a0005183
EISBN: 978-1-62708-186-3
... creep mechanisms that are useful for illustrating the strong stress dependence of dislocation and diffusional flow. ambient temperature Isothermal constitutive modeling physical models strain hardening strain-rate-sensitive flow superplastic flow CONSTITUTIVE RELATIONS for metalworking...
Abstract
Constitutive relations for metal-working include elements of behavior at ambient temperature as well as high-temperature response. This article presents the equations for the strain hardening and strain-rate-sensitive flow, with alternate sections on empirically determined properties, followed by models of constitutive behavior. These models include the isothermal constitutive model and the physical model for superplastic flow. A formal description of the superposition of the operative mechanisms for dynamic recovery at hot-working strain rates is also provided. The article describes creep mechanisms that are useful for illustrating the strong stress dependence of dislocation and diffusional flow.
Series: ASM Handbook
Volume: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005404
EISBN: 978-1-62708-196-2
... to be controlled by lattice diffusion. The problem of diffusional creep was first addressed by Nabarro and Herring ( Ref 16 ). Creep deformation occurs as a result of coordinated atom movement between different interfaces that results in a macroscopic shape change. Intrinsically, this is an extremely slow...
Abstract
This article, to develop an understanding of the underlying mechanisms governing deformation at elevated temperatures, discusses the phenomenological effects resulting from temperature-induced thermodynamic and kinetic changes. It describes the deformation behavior of engineering materials using expressions known as constitutive equations that relate the dependence of stress, temperature, and microstructure on deformation. The article reviews the characteristics of creep deformation and mechanisms of creep, such as power-law creep, low temperature creep, power-law breakdown, diffusional creep, twinning during creep deformation, and deformation mechanism maps. It discusses the creep-strengthening mechanisms for most structural engineering components. The article provides a description of the microstructural modeling of creep in engineering alloys.
Series: ASM Handbook
Volume: 8
Publisher: ASM International
Published: 01 January 2000
DOI: 10.31399/asm.hb.v08.a0003287
EISBN: 978-1-62708-176-4
... through the grain interiors provides the most rapid path, then the diffusivity, D , is equal to the lattice or bulk self-diffusion coefficient. This process is known as Nabarro-Herring creep. Alternatively, diffusion may be more rapid through the grain boundaries, in which case D in Eq 4 is replaced...
Abstract
Creep deformation is normally studied by applying either a constant load or a constant true stress to a material at a sufficiently high homologous temperature so that a measurable amount of creep strain occurs in a reasonable time. This article provides the phenomenological descriptions of creep and explains the testing and mechanism of creep in crystalline solids. It also presents information on the creep response of crystalline and amorphous solids.
Series: ASM Handbook
Volume: 24
Publisher: ASM International
Published: 15 June 2020
DOI: 10.31399/asm.hb.v24.a0006557
EISBN: 978-1-62708-290-7
... such as argon, nitrogen, and helium are often used in the processing environments for metal components. There are four main mechanisms by which pores are eliminated by HIP: plastic flow, power-law creep, Coble (grain-boundary) creep, and Nabarro-Herring (lattice) creep ( Ref 30 ). In sum, all mechanisms...
Abstract
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.
Series: ASM Handbook
Volume: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005433
EISBN: 978-1-62708-196-2
... and accommodation by dislocations. Diffusional Accommodation Models During the later part of 1960s, there were attempts to explain region II in Fig. 1 (the superplastic regime) using diffusional creep models ( Ref 18 , 19 ). Both Nabarro-Herring ( Ref 20 , 21 ) and Coble creep ( Ref 22 ) were also...
Abstract
This article presents a mechanical description of superplasticity and discusses constitutive equations that are essential for simulating superplastic forming processes, applicable to structural superplasticity. It presents the phenomenological constitutive equations of superplasticity and classical physical constitutive equations. The article also reviews the accommodation mechanisms that are divided into two major groups, namely, diffusional accommodation and accommodation by dislocations.
Series: ASM Handbook
Volume: 20
Publisher: ASM International
Published: 01 January 1997
DOI: 10.31399/asm.hb.v20.a0002460
EISBN: 978-1-62708-194-8
Abstract
This article focuses on the relationships among material properties and material structure. It summarizes the fundamental characteristics of metals, ceramics, and polymers. The article provides information on the crystal structure, the atomic coordination, and crystalline defects. It discusses the relevance of the properties to design. The article describes the common means for increasing low-temperature strength and presents an example that shows structure-property relationships in nickel-base superalloys for high-temperature applications. The relationships of microstructure with low-temperature fracture, high-temperature fracture, and fatigue failure are also discussed.
Book: Casting
Series: ASM Handbook
Volume: 15
Publisher: ASM International
Published: 01 December 2008
DOI: 10.31399/asm.hb.v15.a0005293
EISBN: 978-1-62708-187-0
... 247, René 125) 1185 2165 175 25 4 Mechanisms of Pore Closure during HIP There are four main mechanisms by which pores are eliminated during HIP: Plastic flow Power law creep Coble (grain-boundary) creep Nabarro-Herring (lattice) creep Given appropriate temperature...
Abstract
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.
Series: ASM Handbook
Volume: 24
Publisher: ASM International
Published: 15 June 2020
DOI: 10.31399/asm.hb.v24.a0006552
EISBN: 978-1-62708-290-7
... densifying mechanism until more diffusion-based creep processes take over, such as Nabarro-Herring creep, or bulk creep, and Coble creep, or grain-boundary creep ( Ref 4 , 5 ). With these densification mechanisms and a sufficiently long soak time at HIP conditions, internal defects can be completely erased...
Abstract
Hot isostatic pressing (HIP) is widely used within the additive manufacturing (AM) industry to improve material performance and ensure quality. This article is a detailed account of the HIP process, providing information on its equipment set up and discussing the applications, economics, and advantages of the process. The discussion also covers the use of HIP for additively manufactured material to eliminate internal defects, the HIP parameters required to eliminate internal defects, and the influence of HIP on the microstructure and properties of HIP additively manufactured material.
Book Chapter
Series: ASM Handbook
Volume: 8
Publisher: ASM International
Published: 01 January 2000
DOI: 10.31399/asm.hb.v08.a0003288
EISBN: 978-1-62708-176-4
... ). Fortunately, all these mechanisms can be fitted into two basic categories: diffusional creep and dislocation creep. In diffusional creep, diffusion of single atoms or ions either by bulk transport (Nabarro-Herring creep) or by grain-boundary transport (Coble creep) leads to a Newtonian viscous type...
Abstract
This article reviews the basic equipment and methods for creep and creep rupture testing. It begins with a discussion on the creep properties, including stress and temperature dependence, as well as of the extrapolation techniques that permit estimation of the long-term creep and rupture strengths of materials. The article describes the different types of equipment for determination of creep characteristics, including test stands, furnaces, and extensometers. It also discusses the different testing methods for creep rupture: constant-load testing and constant-stress testing. The article presents other testing considerations and concludes with information on stress relaxation testing.
Book: Powder Metallurgy
Series: ASM Handbook
Volume: 7
Publisher: ASM International
Published: 30 September 2015
DOI: 10.31399/asm.hb.v07.a0006042
EISBN: 978-1-62708-175-7
...-dependent densification mechanisms take over. Power-law creep becomes the dominant mechanism for a short period of time until Nabarro-Herring creep and Coble creep diffusion mechanisms take over. Professor Michael Ashby and his research group at Cambridge University, United Kingdom, provided an extensive...
Abstract
This article discusses metal powder processing via hot isostatic pressing (HIP) and HIP cladding when metal powders are being employed in the cladding process. It traces the history of the process and details the equipment, pressing cycle, and densification mechanisms for HIP. The article describes the available process routes for fabricating products using HIP and the steps involved in the production of a part via direct HIP of encapsulated gas-atomized spherical powder. It concludes with information on the microstructures of 316L stainless steel HIP powder metallurgy valve body and a list of the mechanical properties of several powder metallurgy alloys.
Series: ASM Handbook
Volume: 13A
Publisher: ASM International
Published: 01 January 2003
DOI: 10.31399/asm.hb.v13a.a0003590
EISBN: 978-1-62708-182-5
..., at which creep mechanisms become operative. The three important creep mechanisms in oxides are grain- boundary sliding, Herring-Nabarro creep, and climb. Grain-boundary sliding allows relative motion along the inherently weak boundaries. Herring-Nabarro creep allows grain elongation by diffusion of ions...
Abstract
This article examines the characteristics and behavior of scale produced by various types of oxidation. The basic models, concepts, processes, and open questions for high-temperature gaseous corrosion are presented. The article describes the development of geometrically induced growth stresses, transformation stresses, and thermal stresses in oxide scales. It discusses the ways in which stresses can be relieved. The article provides information on catastrophic oxidation, internal oxidation, sulfidation, alloy oxidation, selective oxidation, and concurrent oxidation. It illustrates the relationships between scale morphologies on binary alloys and concludes with a discussion on metal dusting and chlorine corrosion.
Book: Composites
Series: ASM Handbook
Volume: 21
Publisher: ASM International
Published: 01 January 2001
DOI: 10.31399/asm.hb.v21.a0003448
EISBN: 978-1-62708-195-5
... in nature to Nabarro-Herring creep and is associated with atomic transport in the matrix around the reinforcement phase, incorporating the stress carried by the reinforcement phase, size of the reinforcement, and parameters related to the mass transport in the vicinity of the interface (e.g., boundary...
Abstract
Metal-matrix composites (MMCs) are used in structural applications, and in applications requiring wear resistance, thermal management, and weight savings. This article summarizes the mechanical and thermal properties of discontinuously reinforced aluminum MMCs, laminated metallic composites, and continuously aligned fiber reinforced MMCs.
Series: ASM Handbook
Volume: 20
Publisher: ASM International
Published: 01 January 1997
DOI: 10.31399/asm.hb.v20.a0002472
EISBN: 978-1-62708-194-8
... and strain components associated with creep processes; stress and temperature dependence; fracture at elevated temperatures; and environmental effects. The article describes the basic presentation and analysis methods for creep rupture. It provides information on the application of these methods to materials...
Abstract
This article reviews the basic mechanisms of elevated-temperature behavior and associated design considerations, with an emphasis on metals. It discusses the key concepts of elevated-temperature design. These include plastic instability at elevated temperatures; deformation mechanisms and strain components associated with creep processes; stress and temperature dependence; fracture at elevated temperatures; and environmental effects. The article describes the basic presentation and analysis methods for creep rupture. It provides information on the application of these methods to materials selection and the setting of basic design rules. The article examines the limitations of high-temperature components as well as the alternative design approaches and tests for most high-temperature components.
Book: Fractography
Series: ASM Handbook
Volume: 12
Publisher: ASM International
Published: 01 June 2024
DOI: 10.31399/asm.hb.v12.a0006843
EISBN: 978-1-62708-387-4
... coalescence (MVC), cleavage, or intergranular decohesion (when creep processes are not activated). When overload is the principal cause of fracture, most common structural alloys fail by MVC. These microvoids nucleate at regions of localized strain discontinuity, such as those associated with second-phase...
Abstract
This article presents the concept of fracture mechanisms in general terms in order to impart a practical understanding as well as enable readers to develop the ability to identify the basic fracture mechanisms correctly based on microscope observations. The key microscopic features of fracture surfaces are described and illustrated for the important types of fracture mechanisms. It provides a detailed discussion on environmentally assisted crack initiation and growth.
Book: Fractography
Series: ASM Handbook
Volume: 12
Publisher: ASM International
Published: 01 June 2024
DOI: 10.31399/asm.hb.v12.a0006874
EISBN: 978-1-62708-387-4
... mode (a) Progressive fracture mode Ductile overload Brittle overload Fatigue Creep Visual, 1 to 50× (fracture surface) Necking or distortion in direction consistent with applied loads Dull, fibrous fracture Shear lips Little or no distortion Flat fracture Bright...
Abstract
Identification of the fracture mechanism is one of the principal responsibilities of a failure analyst and is an important component of any root-cause analysis. This article explores the varied mechanisms responsible for metal fracture, particularly regarding fractography. The behavior of engineering materials at fracture is based on a large number of interrelated characteristics from the atomic level to the component level. These characteristics range from ductile to brittle at the microscale and macroscale levels. Fundamental relative ductility results from the type of electronic bonding, the crystal structure, and the broader long-range degree of order. It provides detailed discussion on ductile fracture, brittle fracture, mixed fracture, embrittlement, stress-corrosion cracking.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006787
EISBN: 978-1-62708-295-2
... salts or metals can induce other secondary mechanisms, such as galvanic corrosion, crevice corrosion, and pitting corrosion; creep; and fatigue. Impingement by solid particles can contribute to erosion-corrosion, or it can accelerate corrosion in the various gaseous and molten environments. Primary...
Abstract
High-temperature corrosion can occur in numerous environments and is affected by various parameters such as temperature, alloy and protective coating compositions, stress, time, and gas composition. This article discusses the primary mechanisms of high-temperature corrosion, namely oxidation, carburization, metal dusting, nitridation, carbonitridation, sulfidation, and chloridation. Several other potential degradation processes, namely hot corrosion, hydrogen interactions, molten salts, aging, molten sand, erosion-corrosion, and environmental cracking, are discussed under boiler tube failures, molten salts for energy storage, and degradation and failures in gas turbines. The article describes the effects of environment on aero gas turbine engines and provides an overview of aging, diffusion, and interdiffusion phenomena. It also discusses the processes involved in high-temperature coatings that improve performance of superalloy.
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