On the contribution of concurrent grain growth to strain sensitive flow of a superplastic Al-Cu eutectic alloy
01 Apr 1987-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer-Verlag)-Vol. 18, Iss: 3, pp 417-424
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
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TL;DR: The characteristics of fracture by cavitation in superplastic materials are reviewed in this paper, with particular attention paid to the theoretical developmental aspects of cavity nucleation, cavity growth and cavity interlinkage.
Abstract: The characteristics of fracture by cavitation in superplastic materials are reviewed. Particular attention is paid to the theoretical developmental aspects of cavity nucleation, cavity growth and cavity interlinkage. Various factors, including grain boundary sliding, impurity atoms or particles, phase proportion, deformation temperature, strain rate, strain and grain size, are discussed. Finally, methods for controlling cavitation during superplastic deformation are summarized, and problems which require further work are also presented.
70 citations
TL;DR: In this article, the role of grain size on tensile ductility is discussed in high-temperature plastic flow of high-purity A1 2 O 3 and MgO-doped A 1 2 O3 in a temperature range 1300 ∼ 1450°C.
Abstract: High-temperature plastic flow of high-purity A1 2 O 3 and MgO-doped A1 2 O 3 has been examined in a temperature range 1300 ∼ 1450°C. High-purity A1 2 O 3 with an initial grain size of about 0.9 μm is characterized by large strain-hardening rate and small tensile ductility up to 20%. The addition of 0.1 wt% MgO into A1 2 O 3 results in a decrease of strain-hardening rate and improves tensile ductility. The tensile elongation up to 70% is obtained in MgO-doped A1 2 O 3 . The difference in plastic flow behavior between pure and MgO-doped A1 2 O 3 is caused by the difference in grain growth during high-temperature deformation between the two materials. The grain growth inhibition caused by the MgO addition is very important to improve the tensile ductility. The tensile ductility of MgO-doped A1 2 O 3 is slightly but further improved in a temperature-increasing test. The role of grain size on tensile ductility is discussed in this paper.
68 citations
TL;DR: In this article, the superplastic Zn-22% Al eutectoid alloy was tested over a range of strain rates at 503 K using specimens machined with the rolling direction perpendicular to the tensile axis.
55 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
References
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TL;DR: In this article, the high temperature steady state deformation behavior of PbSn eutectic alloy was investigated over wide ranges of grain size (9.7 − 32.0 μm), temperature (298 − 443 K) and strain rate (10 −7 − 10 −2 s −1 ), after stability of microstructure and strength had been achieved through prior tensile deformation.
149 citations
TL;DR: In this paper, the shape of the log stress-log strain rate curve for the Al-33 wt pct Cu eutectic alloy was examined and the inherent grain growth of the very fine grains which occurs during deformation, and the strain dependence of m at low strains, were shown to be the causes of the familiar shape of log stresslog strain curve for Al-Cu alloy.
Abstract: The usual method of measuring the strain rate sensitive ‘m’ values of superplastic materials through differential cross-head speed is found to result in improperly definedm values;m is found to depend strongly on the strain to which the material is subjected, especially at low strains. In this connection, the shape of the log stress-log strain rate curve is examined for the Al-33 wt pct Cu eutectic alloy. The inherent grain growth of the very fine grains which occurs during deformation, and the strain dependence ofm at low strains, are shown to be the causes of the familiarS shape of the log stress-log strain rate curves for the Al-Cu alloy. At high strains (15 to 20 pct and higher) where the stress is no longer importantly strain sensitive, the log stress-log strain rate curve is a straight line of slope near 0.5. The elongation at fracture also does not go through a maximum but continues to increase slowly to the lowest strain rate examined: 10-7 per s.
138 citations
TL;DR: The microstructural aspects of the superplastic phenomenon are reviewed in this article, where experimental results of a very large number of investigations are critically analysed in the context of: grain shape and size; grain growth; grain boundary sliding and migration, grain rotation and rearrangement; diffusion and dislocation activity.
Abstract: The microstructural aspects of the superplastic phenomenon are reviewed. The experimental results of a very large number of investigations are critically analysed in the context of: grain shape and size; grain growth; grain boundary sliding and migration, grain rotation and rearrangement; diffusion and dislocation activity. It is shown, that in spite of often conflicting evidence in the literature, a common pattern of microstructural behaviour emerges for all the materials and conditions investigated to date.
124 citations
TL;DR: Stress-strain curves have been obtained for the superplastically deformed Al-Cu eutectic tested in tension under constant true strain-rate conditions and it is shown that constant flow stress conditions do not obtain and that, after an initial transient, the flow stress is linearly related to natural tensile strain this article.
Abstract: Stress-strain curves have been obtained for the superplastically deformed Al-Cu eutectic tested in tension under constant true strain-rate conditions. It is shown that constant flow stress conditions do not obtain and that, after an initial transient, the flow stress is linearly related to natural tensile strain. Optical metallography has been employed to follow the variation of both inter-phase particle separation and α-Al grain size with strain and it is concluded that the observed strain hardening is due mainly to grain coarsening.
89 citations