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diffusion creep
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Book Chapter
Series: ASM Handbook
Volume: 14A
Publisher: ASM International
Published: 01 January 2005
DOI: 10.31399/asm.hb.v14a.a0004018
EISBN: 978-1-62708-185-6
...Abstract Abstract 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...
Abstract
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.
Series: ASM Handbook
Volume: 22B
Publisher: ASM International
Published: 01 November 2010
DOI: 10.31399/asm.hb.v22b.a0005512
EISBN: 978-1-62708-197-9
... also depends on the properties (yield stress, creep behavior, diffusion constants) of the materials being joined and on the condition of the two faying surfaces. Typically, the two surfaces to be bonded are far from smooth on the atomic scale, and the initial contact area between the two surfaces...
Abstract
The goals of modeling diffusion bonding can be regarded as twofold: to optimize the selection of the process variables for a given material and to provide an understanding of the mechanisms by which bonding is achieved. This article describes the existing models of diffusion bonding with an assumption that the surfaces to be joined are free of contaminants and oxide, that bonding occurs between similar materials, and that the materials are single-phase metals. It discusses the mechanisms considered for diffusion bonding and limitations of existing models.
Series: ASM Handbook
Volume: 14B
Publisher: ASM International
Published: 01 January 2006
DOI: 10.31399/asm.hb.v14b.a0005146
EISBN: 978-1-62708-186-3
... (shear) spinning, rubber-pad forming, stretch forming, contour roll forming, creep forming, vacuum forming, drop hammer forming, joggling, and explosive forming. alpha alloys alpha-beta alloys Bauschinger effect cold forming contour roll forming creep forming diffusion bonding drop hammer...
Abstract
This article describes different types of titanium alloys, including alloy Ti-6Al-4V, alpha and near-alpha alloys, and alpha-beta alloys. It explains the formability of titanium alloys with an emphasis on the Bauschinger effect. The article provides information on the tool materials and lubricants used in the forming process. It provides information on the cold and hot forming, superplastic forming, and combination of superplastic forming/diffusion bonding. The article discusses the various forming processes of these titanium alloys, including press-brake forming, power (shear) spinning, rubber-pad forming, stretch forming, contour roll forming, creep forming, vacuum forming, drop hammer forming, joggling, and explosive forming.
Series: ASM Handbook
Volume: 8
Publisher: ASM International
Published: 01 January 2000
DOI: 10.31399/asm.hb.v08.a0003266
EISBN: 978-1-62708-176-4
... creep ( Ref 10 ). In diffusional creep, diffusion of single atoms or ions, either by bulk transport (Nebarro-Herring creep) or by grain-boundary transport (Coble creep) leads to Newtonian viscous flow. In this type of creep, steady-state creep rates vary linearly. At low stresses, diffusional creep...
Abstract
This article emphasizes short-term tension and compression testing of metals at high temperatures. It describes the effect of temperature on deformation and strain hardening, occurrence of high-temperature creep in structural alloys, and the performing of mechanical testing for high-temperature structural alloys. The article discusses hot tension testing and measurements of temperature and strain in the hot tension testing. It also provides an overview of hot compression testing.
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
..., including low stress behavior, concurrent grain growth, and high stress behavior. ambient temperature creep mechanisms diffusion creep diffusional flow dislocation creep Nabarro-Herring creep strain hardening CONSTITUTIVE RELATIONS for metalworking include elements of behavior at ambient...
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.
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
..., by characterizing the stress and temperature dependence of the creep rate, it is often possible to identify the rate-controlling mechanism for a particular material. Commonly, it is observed that the activation energy for creep is the same as that for diffusion; hence, the term exp − Q c / kT 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: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005411
EISBN: 978-1-62708-196-2
... coalesce to advance the crack. Such crack growth is dominantly intergranular. The kinetics of cavity growth have been modeled as either diffusive growth or as growth constrained by the deformation of the surrounding grains. These have led to models for rationalizing the correlation between creep crack...
Abstract
The overarching goal of life-prediction research is to develop models for the various types of time dependencies in the crack-tip damage accumulation that occur in materials subjected to elevated temperatures. This article focuses on describing the models based on creep, oxidation kinetics, evolution of crack-tip stress fields due to creep, oxygen ingress, and change in the microstructure. It also provides a summary of creep-fatigue modeling approaches.
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
.... Diffusional creep models do not involve grain rotations that are topologically observed in superplasticity. Ashby and Verrall ( Ref 24 ) proposed a model that explains superplasticity as a transition region between a diffusion-accommodated flow at low strain rates and a diffusion-controlled dislocation...
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.
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.
Series: ASM Handbook
Volume: 6
Publisher: ASM International
Published: 01 January 1993
DOI: 10.31399/asm.hb.v06.a0001352
EISBN: 978-1-62708-173-3
... stresses from fabrication. The loading may be continually increasing, as with a conventional tensile test, or static, as with creep tests. Again, these behaviors are quite different. Additionally, some interlayer/base-metal interfaces have been shown to be susceptible to stress-corrosion cracking when...
Abstract
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.
Series: ASM Handbook
Volume: 6A
Publisher: ASM International
Published: 31 October 2011
DOI: 10.31399/asm.hb.v06a.a0005556
EISBN: 978-1-62708-174-0
... because these types of welds are, mechanically, quite anisotropic. This includes the case where interlayers may be subjected to residual stresses from fabrication. The loading may be continually increasing, as with a conventional tensile test, or static, as with creep tests. Again, these behaviors...
Abstract
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.
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
... describes 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...
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: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006787
EISBN: 978-1-62708-295-2
.... Appl. Phys. , Vol 21 , 1950 , p 437 – 445 10.1063/1.1699681 126. Coble R.L. , A Model for Boundary Diffusion Controlled Creep in Polycrystalline Materials , J. Appl. Phys. , Vol 34 , 1963 , p 1679 – 1682 10.1063/1.1702656 127. Weertman J. , Theory of Steady-State...
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.
Book Chapter
Series: ASM Handbook
Volume: 6A
Publisher: ASM International
Published: 31 October 2011
DOI: 10.31399/asm.hb.v06a.a0005606
EISBN: 978-1-62708-174-0
... contact: limited to a few asperities (room temperature). (b) First stage: deformation of surface asperities by plastic flow and creep. (c) Second stage: grain-boundary diffusion of atoms to the voids and grain-boundary migration. (d) Third stage: volume diffusion of atoms to the voids During...
Abstract
This article provides a qualitative summary of the theory of diffusion bonding, as distinguished from the mechanisms of other solid-state welding processes. Diffusion bonding can be achieved for materials with adherent surface oxides, but the resultant interface strengths of these materials are considerably less than that measured for the parent material. The article describes three stages of diffusion bonding: microasperity deformation, diffusion-controlled mass transport, and interface migration. It concludes with information on diffusion bonding with interface aids.
Series: ASM Handbook
Volume: 6
Publisher: ASM International
Published: 01 January 1993
DOI: 10.31399/asm.hb.v06.a0001350
EISBN: 978-1-62708-173-3
... bonding process. (a) Initial contact: limited to a few asperities (room temperature). (b) First stage: deformation of surface asperities by plastic flow and creep. (c) Second stage: grain boundary diffusion of atoms to the voids and grain boundary migration. (d) Third stage: volume diffusion of atoms...
Abstract
Diffusion bonding is only one of many solid-state joining processes wherein joining is accomplished without the need for a liquid interface (brazing) or the creation of a cast product via melting and resolidification. This article offers a qualitative summary of the theory of diffusion bonding. It discusses factors that affect the relative difficulty of diffusion bonding oxide-bearing surfaces. These include surface roughness prior to welding, mechanical properties of the oxide, relative hardness of the metal and its oxide film, and prestraining or work hardening of the material. The article describes the mechanism of diffusion bonding in terms of microasperity deformation, diffusion-controlled mass transport, and interface migration. It concludes with a discussion on diffusion bonding with interface aids.
Series: ASM Handbook
Volume: 8
Publisher: ASM International
Published: 01 January 2000
DOI: 10.31399/asm.hb.v08.a0003292
EISBN: 978-1-62708-176-4
... 0 exp ( − Q R T ) where γ ˙ is the shear creep, k is Boltzmann's constant, T is the absolute temperature, D is the diffusion coefficient that characterizes the creep process, G is the shear modulus, b is the Burgers vector, A is a dimensionless constant, d...
Abstract
Studies on mechanical behavior of superplasticity at or above 50" of the melting point lead to the understanding of superplasticity as a creep phenomenon. This article provides a discussion on the four relationships that define the basic deformation characteristics associated with a creep process: the stress and strain rate, strain rate or stress and temperature, strain rate or stress and grain size, and strain contributed by boundary sliding and total strain. The article describes the deformation characteristics and mechanisms of low-stress region, intermediate-stress region, and high-stress region. It also discusses the effect of impurities on superplastic flow and concludes with information on grain growth during testing.
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
... ). These various processes of creep (dislocation controlled as well as diffusion controlled) may be represented on a deformation mechanism map to highlight regimes of stress and temperature where each mechanism, based on current theories, may be operating ( Ref 17 ). However, such maps are only as good...
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.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006781
EISBN: 978-1-62708-295-2
... thermomechanical fatigue testing. Image shows surface oxidation at bottom and oxide spike forming in the center of the specimen. Chemical etchant used highlights aluminum in the microstructure. Microstructure shown as white in image is depleted of aluminum as a result of aluminum diffusion to surface. Source: Ref...
Abstract
Thermomechanical fatigue (TMF) is the general term given to the material damage accumulation process that occurs with simultaneous changes in temperature and mechanical loading. TMF may couple cyclic inelastic deformation accumulation, temperature-assisted diffusion within the material, temperature-assisted grain-boundary evolution, and temperature-driven surface oxidation, among other things. This article discusses some of the major aspects and challenges of dealing with TMF life prediction. It describes the damage mechanisms of TMF and covers various experimental techniques to promote TMF damage mechanisms and elucidate mechanism coupling interactions. In addition, life modeling in TMF conditions and a practical application of TMF life prediction are presented.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003517
EISBN: 978-1-62708-180-1
..., microstructural evaluations, the creep cavitation damage assessment, the oxide-scale-based life prediction, and high-temperature crack growth methods. coating evaluation creep cavitation damage assessment elevated-temperature failure gas turbine blade hardness testing high-temperature crack growth...
Abstract
This article focuses on the life assessment methods for elevated-temperature failure mechanisms and metallurgical instabilities that reduce life or cause loss of function or operating time of high-temperature components, namely, gas turbine blade, and power plant piping and tubing. The article discusses metallurgical instabilities of steel-based alloys and nickel-base superalloys. It provides information on several life assessment methods, namely, the life fraction rule, parameter-based assessments, the thermal-mechanical fatigue, coating evaluations, hardness testing, microstructural evaluations, the creep cavitation damage assessment, the oxide-scale-based life prediction, and high-temperature crack growth methods.