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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: 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.
Image
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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Image
Published: 01 January 2006
Fig. 24 During the intermediate stage of grain switching, grains 1 and 2 (compare with Fig. 23 ) change their shape from that indicated by the solid (initial state) lines to that of the dotted lines. The shape change is provided for by diffusional flow, which can take place by volumetric
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Image
Published: 01 January 2005
Fig. 24 During the intermediate stage of grain switching, grains 1 and 2 (compare with Fig. 23 ) change their shape from that indicated by the solid (initial state) lines to that of the dotted lines. The shape change is provided for by diffusional flow, which can take place by volumetric
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Image
Published: 01 January 1987
), air cool. Sample was tensile tested to failure at 700 °C (1290 °F) and an initial strain rate of 4.4 × 10 −5 /s. Slip lines, smoothened by diffusional flow, are visible on grain boundaries of the elevated-temperature fracture surface. Failure was intergranular and resulted from the nucleation, growth
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Book: Casting
Series: ASM Handbook
Volume: 15
Publisher: ASM International
Published: 01 December 2008
DOI: 10.31399/asm.hb.v15.a0005226
EISBN: 978-1-62708-187-0
..., and the formation of noncrystalline phases. It considers three factors to understand the fundamentals of these changes: heat flow, thermodynamic constraints/conditions at the liquid-solid interfaces, and diffusional kinetics/microsegregation. These factors are described in detail. casting microsegregation...
Abstract
Rapid solidification is a tool for modifying the microstructure of alloys that are obtained by ordinary casting. This article describes the fundamentals of the four microstructural changes, namely, microsegregation, identity of the primary phase, identity of the secondary phase, and the formation of noncrystalline phases. It considers three factors to understand the fundamentals of these changes: heat flow, thermodynamic constraints/conditions at the liquid-solid interfaces, and diffusional kinetics/microsegregation. These factors are described in detail.
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 flow can be derived by first considering the equilibrium concentration of vacancies, C , within a material: (Eq 30) C = C o exp ( − Q f k T ) where Q f is the vacancy formation energy, and C o is the equilibrium vacancy concentration coefficient. Upon...
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.a0005458
EISBN: 978-1-62708-196-2
... it. Subsequently, cavity-growth models were developed; these analyses focused on stress concentrations along the grain boundaries, with diffusional flow relaxing tensile stresses at cavity tips on the grain boundary and higher tensile stresses developing in regions between cavities. This leads to higher vacancy...
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.
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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Image
Published: 01 January 2003
Fig. 9 The Wang-Seigle model for aluminum transport incorporating diffusional flux and viscous flow in the depleted zone. Source: Ref 20
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Image
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: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005433
EISBN: 978-1-62708-196-2
... 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. constitutive model superplastic flow superplasticity phenomenological constitutive equation...
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: 8
Publisher: ASM International
Published: 01 January 2000
DOI: 10.31399/asm.hb.v08.a0003287
EISBN: 978-1-62708-176-4
... present compelling evidence that dislocations interact strongly with particles on a very local scale. Deformation Mechanism Maps The mechanisms of dislocation glide, dislocation climb, and diffusional flow exhibit different stress and temperature dependencies. Thus, the relative contribution...
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
Book: Fractography
Series: ASM Handbook Archive
Volume: 12
Publisher: ASM International
Published: 01 January 1987
DOI: 10.31399/asm.hb.v12.a0000601
EISBN: 978-1-62708-181-8
... cool. Sample was tensile tested to failure at 700 °C (1290 °F) and an initial strain rate of 4.4 × 10 −5 /s. Slip lines, smoothened by diffusional flow, are visible on grain boundaries of the elevated-temperature fracture surface. Failure was intergranular and resulted from the nucleation, growth...
Abstract
This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of pure irons and in identifying and interpreting the morphology of fracture surfaces. The fractographs illustrate the grain-boundary cavitation; slip lines; intergranular fracture; cleavage fracture; notch-impact fracture; oxide inclusions and blowholes; ductile rupture; impact fracture and tensile-test fracture surfaces; fatigue striations; and crack initiation and propagation of pure irons.
Series: ASM Handbook
Volume: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005409
EISBN: 978-1-62708-196-2
... by grain-boundary sliding accommodated by glide/climb of dislocations, m ∼ 0.5 and p ∼ 2. For grain-boundary sliding accommodated by diffusional flow, m ∼ 1 and p ∼ 2 or 3, depending on whether bulk (lattice) or boundary diffusion predominates. It has been shown that superplastic flow in two...
Abstract
This article focuses on the modeling of microstructure evolution during thermomechanical processing in the two-phase field for alpha/beta and beta titanium alloys. It also discusses the mechanisms of spheroidization, the coarsening, particle growth, and phase decomposition in titanium alloys, with their corresponding equations.
Series: ASM Handbook
Volume: 4B
Publisher: ASM International
Published: 30 September 2014
DOI: 10.31399/asm.hb.v04b.a0005966
EISBN: 978-1-62708-166-5
... along a concentration gradient , from higher concentration to lower concentration. If the concentration gradient is maintained or stable, then the flow or flux is maintained. If the diffusional flow reduces the gradient, then the flux diminishes as diffusion proceeds. For a given direction...
Abstract
This article focuses on the mechanisms, models, prevention, correction, and effects associated with decarburization inherited from semi-finished product processing prior to induction heating. It discusses the diffusion of carbon in austenitic iron, which has a face-centered cubic crystal structure that provides an interstitial path for the migration of the relatively small carbon atoms. The article describes the evolution of steel microstructure with progressive decarburization (in air) to a steady-state carbon gradient using an iron-iron carbide phase diagram. It provides useful information on the impact of alloying on vulnerability to decarburization, and the impact of decarburization on the mechanical properties of steels and cast irons. The article also describes the technological operations that potentially cause decarburization and the practical implications for induction hardening.
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
... of this class of material. Research since 1960 has demonstrated only limited diffusion bond properties. Although interface strength can be increased for oxide-bearing materials, it requires considerable surface extension of the faying interfaces to create localized plastic flow of the metal and concurrent oxide...
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
... alloys are prime examples of this class of material. Research since 1960 has demonstrated only limited diffusion bond properties. Although interface strength can be increased for oxide-bearing materials, it requires considerable surface extension of the faying interfaces to create localized plastic flow...
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: 22A
Publisher: ASM International
Published: 01 December 2009
DOI: 10.31399/asm.hb.v22a.a0005425
EISBN: 978-1-62708-196-2
... models that can and are used to predict future applications of the studied process. Figure 1 shows a schematic flow path for the development of models that provide improved understanding of processes, where metallurgical or manufacturing process-based. Fig. 1 Process flow for development...
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.
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