Nucleation of cavities at second phase particles in grain boundaries
TL;DR: In this paper, a kinetic approach is used to explain the nucleation of cavities in grain boundaries at elevated temperature, under the influence of a tensile stress, vacancies cluster together and form cavities.
About: This article is published in Acta Metallurgica.The article was published on 1978-06-01. It has received 237 citations till now. The article focuses on the topics: Nucleation & Grain boundary strengthening.
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TL;DR: In this article, the authors present a methodology that relates the kinetics of material failure on the microstructural level to continuum mechanics, by introducing micro-structural descriptions of damage into the continuum constitutive relations as internal state variables.
666 citations
TL;DR: A review of superplasticity in polycrystalline materials can be found in this article, where the authors present an overview of these new developments using the established behavior of conventional metallic alloys as a standard for comparison with the mechanical properties of new materials.
Abstract: The ability to achieve a high tensile ductility in a polycrystalline material is of interest both from a scientific point of view and also because of potential applications in the materials forming industry. The superplasticity of conventional metallic alloys is now well-documented and understood reasonably well. However, the field of superplasticity has expanded recently beyond the traditional metallic alloys to include evidence of superplastic-like behavior in a very wide range of new and advanced materials. To date, superplasticity has been reported in mechanically alloyed metals, metal matrix composites, ceramics, ceramic matrix composites and intermetallic compounds. This review presents an overview of these new developments using the established behavior of conventional metallic alloys as a standard for comparison with the mechanical properties of these new materials. As well be demonstrated, the new materials often exhibit significant differences in their flow characteristics in comparison with the traditional superplastic metallic alloys. The successful utilization of superplastic materials in forming applications requires an understanding of the failure processes occurring in the materials in terms of both the localization of external flow and the accumulation of internal damage through the nucleation and growth of cavities. These problems are also addressed in this review.
427 citations
TL;DR: In this article, two specially developed techniques were used to study the nucleation and growth of grain-boundary cavities in 304 stainless steel at 0.5 Tm and found that cavities nucleated heterogeneously throughout the creep history and those observed were well in their growth stage.
180 citations
TL;DR: In this paper, a model of cavity nucleation based on the stochastic nature of transgranular creep deformation is presented, and a quantitative assessment of the likely errors of measurement is presented.
170 citations
25 Aug 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of precipitation on grain boundary tortuosity and sliding, and its influence on ductility-dip cracking resistance is discussed in the context of current theories of high temperature creep.
Abstract: The ductility dip cracking susceptibility of two Ni-base filler metals, Filler Metal 52 (59%Ni–29%Cr–9%Fe–1%Mn–1%Al) and Filler Metal 82 (72%Ni–20%Cr–1%Fe–3%Mn–3%Nb) was evaluated using the strain-to-fracture test The analysis of these results and detailed weld metal microstructural characterization (SEM and TEM) was presented in Part I Part II of this work provides new insight into the creep-like, grain boundary sliding mechanism that leads to elevated temperature intergranular cracking in these weld deposits The effect of precipitation on grain boundary tortuosity and sliding, and its influence on ductility-dip cracking resistance is discussed in the context of current theories of high temperature creep Finally, the effect of composition, including both precipitate forming elements and impurity elements, on ductility-dip cracking is discussed
158 citations
References
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01 Apr 1971
TL;DR: In this paper, the problem of sliding at a nonplanar grain boundary is considered in detail, and the results give solutions to the following problems: 1) How much sliding occurs in a polycrystal when neither diffusive flow nor dislocation motion is possible? 2) What is the sliding rate at a wavy or stepped grain boundary when diffusional flow of matter occurs? 3) How is the rate of diffusional creep in polycrystals in which grain boundaries slide? 4) how is this creep rate affected by grain shape, and grain boundary migration? 5)
Abstract: The problem of sliding at a nonplanar grain boundary is considered in detail. The stress field, and sliding displacement and velocity can be calculated at a boundary with a shape which is periodic in the sliding direction (a wavy or stepped grain boundary): a) when deformation within the crystals which meet at the boundary is purely elastic, b) when diffusional flow of matter from point to point on the boundary is permitted. The results give solutions to the following problems. 1) How much sliding occurs in a polycrystal when neither diffusive flow nor dislocation motion is possible? 2) What is the sliding rate at a wavy or stepped grain boundary when diffusional flow of matter occurs? 3) What is the rate of diffusional creep in a polycrystal in which grain boundaries slide? 4) How is this creep rate affected by grain shape, and grain boundary migration? 5) How does an array of discrete particles influence the sliding rate at a grain boundary and the diffusional creep rate of a polycrystal? The results are compared with published solutions to some of these problems.
1,101 citations
TL;DR: Deformations-mechanism maps as discussed by the authors display the fields of stress and temperature in which a particular mechanism of plastic flow is dominant, i.e., dislocation glide, diffusional flow and dislocation creep.
924 citations
TL;DR: In this paper, the authors analyzed the kinetic problem of intergranular fracture at elevated temperatures by the nucleation and growth of voids in the grain boundary and calculated the time-to-fracture.
777 citations
TL;DR: In this article, the authors examined the conditions for cavity formation from equiaxed inclusions in ductile fracture and found that critical local elastic energy conditions are necessary but not sufficient for cavities formation.
Abstract: The previously proposed conditions for cavity formation from equiaxed inclusions in ductile fracture have been examined. Critical local elastic energy conditions are found to be necessary but not sufficient for cavity formation. The interfacial strength must also be reached on part of the boundary. For inclusions larger than about 100A the energy condition is always satisfied when the interfacial strength is reached and cavities form by a critical interfacial stress condition. For smaller cavities the stored elastic energy is insufficient to open up interfacial cavities spontaneously. Approximate continuum analyses for extreme idealizations of matrix behavior furnish relatively close limits for the interfacial stress concentration for strain hardening matrices flowing around rigid non-yielding equiaxed inclusions. Such analyses give that in pure shear loading the maximum interfacial stress is very nearly equal to the equivalent flow stress in tension for the given state of plastic strain. Previously proposed models based on a local dissipation of deformation incompatibilities by the punching of dislocation loops lead to rather similar results for interfacial stress concentration when local plastic relaxation is allowed inside the loops. At very small volume fractions of second phase the inclusions do not interact for very substantial amounts of plastic strain. In this regime the interfacial stress is independent of inclusion size. At larger volume fractions of second phase, inclusions begin to interact after moderate amounts of plastic strain, and the interfacial stress concentration becomes dependent on second phase volume fraction. Some of the many reported instances of inclusion size effect in cavity formation can thus be satisfactorily explained by variations of volume fraction of second phase from point to point.
757 citations