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diffusional creep
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in Fundamental Structure-Property Relationships in Engineering Materials
> Materials Selection and Design
Published: 01 January 1997
Fig. 29 Diffusional creep results from a higher vacancy concentration in regions of a material that experience a tensile stress compared to regions that do not. This results in a vacancy flux from the former to the latter areas, and a mass flux in the opposite direction. This extends
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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.
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
..., 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. creep deformation...
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: 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: 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: 8
Publisher: ASM International
Published: 01 January 2000
DOI: 10.31399/asm.hb.v08.a0003287
EISBN: 978-1-62708-176-4
... of stress and temperature for a given material. Accordingly, the stress and temperature dependencies of the creep rate can be used to identify the relevant creep mechanisms. Diffusional Creep Mechanistically, diffusional creep leads to deformation of grains when the transport of atomic vacancies...
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.
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.
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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in Failures from Various Mechanisms and Related Environmental Factors
> Metals Handbook Desk Edition
Published: 01 December 1998
Fig. 45 Deformation-mechanism maps for (a) thoria-dispersed nickel and (b) type 316 stainless steel. Diffusional flow is a type of creep that occurs at very high temperatures and very low stresses.
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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
... are subject to thermally activated processes that can produce continuous plastic deformation (creep) with the application of a constant stress. For metals, various mechanisms are used to explain creep deformation, but all the mechanisms can fall into two basic categories: diffusional creep and dislocation...
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: 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.
Series: ASM Handbook
Volume: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005458
EISBN: 978-1-62708-196-2
... In early theories of cavitation in metallic materials, several key ideas were developed for creep deformation and then applied to superplastic and conventional hot deformation. In these approaches, creep at low stresses and the diffusional contribution to cavity enlargement were considered the most...
Abstract
Any model that describes the early stage of cavitation must therefore address experimental observations of continuous nucleation, cracklike interface cavities, cavity growth from nanometer-scale sizes, and debonding at particle interfaces and formation of large-faceted cavities. This article summarizes the microstructural details of the early stages of cavitation in metals for understanding the interface-constrained plasticity cavitation model. It discusses formulation, predictions and implications, involved in analysis of cavitation under constrained conditions.
Series: ASM Handbook
Volume: 24A
Publisher: ASM International
Published: 30 June 2023
DOI: 10.31399/asm.hb.v24A.a0006964
EISBN: 978-1-62708-439-0
... with diffusional creep—becomes relevant. For example, obvious grain-boundary sliding has been observed in an AM Al-Mg-Zr alloy at 260 °C (500 °F) ( Ref 8 ). In an AM Inconel 738LC (IN738LC), grain growth from 24 to 100 μm can lead to ~3× longer creep lifetime at 850 °C (1560 °F) ( Ref 6 ). During creep...
Abstract
This article briefly introduces the concept of creep properties of additively manufactured (AM) alloys, with a focus on the effects of the characteristic microstructure of AM alloys on creep performance. Relevant postprocessing treatment also is discussed, in relation to improved creep performance based on the improvement of AM initial microstructure.
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
... the yield stress of the material, and that subsequently, bonding continues by various diffusional processes (including creep). The next qualitative model was proposed by King and Owczarksi ( Ref 4 ), who suggested that bonding takes place in three stages. The first two stages were as described...
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: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005425
EISBN: 978-1-62708-196-2
... transformations based on classical nucleation theory and diffusional growth, and grain growth, among others, in the 1940s to1960s. Beginning in the 1980s, the incorporation of the fundamental concepts of thermodynamics and thermal physics (due to, for example, Gibbs, Ising, and others) led to a great expansion...
Abstract
This article provides a brief historical perspective, a classification of metallurgical processes, basic model development efforts, and an overview of the potential future directions for the modeling of metals processing. It describes the classification of material behavior models, which can be grouped broadly into three classes: statistical, phenomenological, and mechanistic models. The article also presents an overview of the potential directions for the modeling of metals processing.
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 Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003546
EISBN: 978-1-62708-180-1
..., during straight and level flight, aircraft jet engines have essentially constant temperatures and imposed loads, where steady-state creep (and the environment) are the primary damage mechanisms. During takeoff and landing, however, the transient demand for more power output induces load and temperature...
Abstract
Thermomechanical fatigue (TMF) refers to the process of fatigue damage under simultaneous changes in temperature and mechanical strain. This article reviews the process of TMF with a practical example of life assessment. It describes TMF damages caused due to two possible types of loading: in-phase and out-of-phase cycling. The article illustrates the ways in which damage can interact at high and low temperatures and the development of microstructurally based models in parametric form. It presents a case study of the prediction of residual life in a turbine casing of a ship through stress analysis and fracture mechanics analyses of the casing.
Series: ASM Handbook
Volume: 14B
Publisher: ASM International
Published: 01 January 2006
DOI: 10.31399/asm.hb.v14b.a0005147
EISBN: 978-1-62708-186-3
... and strain rate, the value of the m -peak is typically in the range of 0.7 to 0.9 and increases with decreasing grain size. The value of m also exhibits a maximum as a function of temperature. The effects of grain size and temperature are closely tied to the diffusional creep contribution during...
Abstract
This article discusses many of the processes and related considerations involved in the forming of superplastic sheet metal parts. It reviews the requirements for superplasticity and describes the characteristics of superplastic metals. The characterization of superplastic behavior includes the characterization of plastic flow, internal cavitation, and fracture behavior. Processing variables needed for the overall characterization of superplastic behavior are summarized. The article discusses the superplastic forming methods, namely, blow forming, vacuum forming, thermoforming, deep drawing, superplastic forming/diffusion bonding, forging, extrusion, and dieless drawing. It provides information on superelastic forming equipment and tooling. The article explains the thinning characteristics and quick plastic forming and its technological elements. It describes the manufacturing practice of the process. The article concludes with a discussion on the superplastic behavior in iron-base alloys.
Book: Fatigue and Fracture
Series: ASM Handbook
Volume: 19
Publisher: ASM International
Published: 01 January 1996
DOI: 10.31399/asm.hb.v19.a0002410
EISBN: 978-1-62708-193-1
... Abstract This article discusses fracture, fatigue, and creep of nickel-base superalloys with additional emphasis on directionally solidified and single-crystal applications. It analyzes the physical metallurgy of these alloys. The effects of grain boundary and grain size on failure...
Abstract
This article discusses fracture, fatigue, and creep of nickel-base superalloys with additional emphasis on directionally solidified and single-crystal applications. It analyzes the physical metallurgy of these alloys. The effects of grain boundary and grain size on failure are summarized. The article also discusses the effects of microstructure and extrinsic parameters on fatigue crack propagation (FCP). It details the modeling of FCP rates and creep and creep-fatigue crack growth rates.
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