Activation energy for superplastic deformation of an AlCu eutectic alloy
TL;DR: In this paper, the authors define a vitesse de deformation differentielle entre 440 and 540 C. La sensibilite a la vitez de deformations pendant la deformation superplastique est de 0,59, elle ne depend pas de maniere significative de la temperature.
About: This article is published in Scripta Metallurgica.The article was published on 1985-12-01. It has received 16 citations till now. The article focuses on the topics: Deformation (meteorology) & Superplasticity.
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TL;DR: In this article, the authors evaluated the constitutive relationship for superplastic deformation of IN718 superalloy after prestraining, and the results showed that the s-−strain rate (SRS) data obtained beyond a certain strain level represent a reasonable steadystate condition.
38 citations
20 Jan 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, an Al-33% Cu eutectic alloy was processed by high pressure torsion (HPT) at a pressure of 6.0 GPa for 1/4 to 10 turns, and tensile tests were conducted at a temperature of 723 K on specimens processed through 5 and 10 turns of HPT.
Abstract: An Al–33% Cu eutectic alloy was processed by high-pressure torsion (HPT) at a pressure of 6.0 GPa for 1/4 to 10 turns. Examination after processing showed a gradual evolution to a reasonable level of hardness and microstructural homogeneity after 5 or more turns. Tensile tests were conducted at a temperature of 723 K on specimens processed through 5 and 10 turns of HPT. These specimens exhibited excellent superplastic properties with a maximum elongation of ∼1250% at strain rates lower than 10−3 s−1. The results also showed that the maximum elongation is displaced to a faster strain rate when the HPT processing is conducted to a higher number of turns. An analysis demonstrates that superplastic flow in the Al–Cu alloy processed by HPT is well described by a theoretical relationship that was developed for conventional superplastic materials.
38 citations
TL;DR: The relationship between flow stress and strain rate is sigmoidal with maximum ductilities occurring at intermediate strain rates in the superplastic Region II and the necks are very diffuse in Region II.
Abstract: Experiments were conducted on the Al-33% Cu eutectic alloy in both an annealed and an as-extruded condition. For both conditions, the relationship between flow stress and strain rate is sigmoidal with maximum ductilities occurring at intermediate strain rates in the superplastic Region II. Specimens fail by necking at the faster strain rates in Region III, but the severity of necking is reduced with decreasing strain rate and the necks are very diffuse in Region II. There is extensive internal cavitation in the fractured specimens, especially at lower strain rates and in the vicinity of the fracture tip. It was observed that cavities form preferentially on theα-θ interphase boundaries. It is shown by calculation that the observed change from small rounded cavities to large cavities elongated along the tensile axis is reasonably consistent with the theories of cavity growth in fine-grained superplastic alloys
30 citations
TL;DR: In this paper, it was shown that the stress-strain curves rapidly attain a steady-state value at strain rates below ′10-4 s-1, and there is a sigmoidal relationship between stress and strain rate which may be obtained using several different testing procedures.
Abstract: Experiments were conducted to determine the mechanical properties of the superplastic Al-33 Pct Cu eutectic alloy at temperatures from 673 to 723 K. Specimens were tested in a well-annealed condition and there was no evidence for grain growth even at the lowest experimental strain rate of 6.7 × 1(10-7 s-1. It is shown that the stress-strain curves rapidly attain a steady-state value at strain rates below ′10-4 s-1, and there is a sigmoidal relationship between stress and strain rate which may be obtained using several different testing procedures. The maximum elongation to failure recorded in these experiments was 1475 Pct at an initial strain rate of 1.3 × 10-5 s-1. The true activation energy for plastic flow is 175 ±11 kJ mol-1 in the superplastic region II, but it increases to 299 ± 18 kJ mol-1 at low strain rates in region I. The exponent of the inverse grain size is 2.1 ±0.3 in region II. These results show that, when the grains size is stable, there is a genuine region I in the Al-33 Pct Cu alloy at initial strain rates below ∼10-5 s-1.
28 citations
TL;DR: In this article, the authors investigated flow behavior and micro-structural evolution in an Al-Cu eutectic alloy of equiaxed grains over e ≃ 2× 10−6 to 2 × 10−2 s−1 and T = 400° to 540 °C.
Abstract: Flow behavior and microstructural evolution in an Al-Cu eutectic alloy of equiaxed grains were investigated over e ≃ 2× 10−6 to 2 × 10−2 s−1 andT = 400° to 540 °C Depending on the test conditions, there appeared either strain hardening or strain softening predominantly in the early part of the σ-e curves The microstructural observations showed evidence for grain growth, development of zig-zag boundaries, dislocation interactions, and cavitation The grain growth adequately accounts for the observed strain hardening at higher temperatures and lower strain rates However, at lower temperatures the strain hardening can be only partly accounted for by the observed grain growth; under this condition, some dislocation interactions also contribute to the strain hardening The presence of cavitation causes strain softening predominantly at higher strain rates Therefore, to develop a proper understanding of the superplastic behavior of the Al-Cu eutectic alloy, it is necessary to take into account the influence of dislocation interactions and cavitation along with that of grain growth
26 citations
References
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TL;DR: In this paper, the authors measured the contribution of boundary sliding in the superplastic Zn-22% Al eutectoid alloy at an elongation of 100% and showed that the sliding contribution is a maximum in the region II and a decrease in the less region I and III.
102 citations
TL;DR: In this article, a technique is presented to calculate grain boundary widths and grain boundary diffusion coefficients in metals and nonmetals using grain growth, sintering, diffusion and/or creep data.
Abstract: A technique is presented to calculate grain‐boundary widths and grain‐boundary diffusion coefficients in metals and nonmetals using grain growth, sintering, diffusion and/or creep data. High‐purity metals yield boundary widths of the order of a few atomic diameters, whereas ionic materials yield ``effective boundary widths'' orders‐of‐magnitude wider.
94 citations
50 citations
TL;DR: In this paper, the authors measured the rate of migration of a triple junction formed between a sub-boundary in the Al and the lamellar interface and found that the interface diffusion coefficient was 1.1 × 10 3 exp [−(23,300/ RT )] between 350 and 500°C.
45 citations
TL;DR: In this article, the activation energy at constant stress, Qσ, is not the same as activation energy in constant strain rate, Qϵ, and that they are related by Qσ = (1/m) where m is the strain-rate sensitivity index.
Abstract: The equations of superplastic flow are used to show that for superplastic flow the activation energy at constant stress, Qσ, is not the same as the activation energy at constant strain rate, Qϵ, and that they are related by Qσ = (1/m) Qϵ where m is the strain-rate sensitivity index. Subsequently, it is shown that this predicted relation is in agreement with experimental observations and can account for discrepancies in the interpretation of activation energy measurements on superplastic materials.
Die Gleichungen des superplastischen Fliesens werden benutzt, um zu zeigen, das fur superplastisches Fliesen die Aktivierungsenergie bei konstanter Spannung Qσ nicht gleich der Aktivierungsenergie bei konstanter Dehnungsgeschwindigkeit Qϵ ist und das sie durch Qσ = (1/m) Qϵ verknupft sind, wobei m der Empfindlichkeitskoeffizient der Dehnungsgesenwindigkeit ist. Darauf wird gezeigt, das diese Beziehung in Ubereinstimmung mit experimentellen Beobachtungen ist und die Diskrepanzen bei der Interpretation der Aktivierungsenergiemessungen an superplastischen Materialien erklaren kann.
20 citations