Superplastic behaviour of annealed AA 8090 Al-Li alloy
TL;DR: In this paper, high temperature flow behavior and microstructural evolution were investigated in an annealed AA 8090 Al-Li alloy over the temperature range 623 - 803 K and strain rate range ~ 6 × 106 - 3 × 102 s-1.
Abstract: High temperature flow behaviour and microstructural evolution were investigated in an annealed AA 8090 Al - Li alloy over the temperature range 623 - 803 K and strain rate range ~ 6 × 106 - 3 × 102 s-1. Stress - strain rate data, obtained using a differential strain rate test technique and plotted in log - log scale, exhibited three regions I, II, and III, with increasing strain rate. In these regions, the values of strain rate sensitivity index m and the activation energy for deformation were determined to be 0.17, 0.43, and 0.17; and 758.8, 93.3, and 184.3 kJ mol-1, respectively. The stress - strain curves obtained from constant strain rate tests exhibited flow hardening at lower strain rates and higher temperatures whereas flow softening occurred at higher strain rates and lower temperatures. The microstructural evolution revealed the dominance of grain growth under the former conditions and dynamic recrystallisation under the latter conditions. Ductility and m were found to increase with temp...
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TL;DR: The tensile superplasticity of a Ni/Si3N4 composite synthesized by electrodeposition was characterized for the first time in this article, where a maximum elongation of 635% was obtained at a temperature of 713 K and a strain rate of 1.5 s−1.
29 citations
15 Sep 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the low-temperature superplasticity of Si3N4/Ni-Co nanocomposite was investigated for the first time at temperatures ranging from 673 to 823 K and at constant strain rates from 1.5 to 1.6 s−1.
Abstract: In this paper, the low-temperature superplasticity of the electrodeposited Si3N4/Ni–Co nanocomposite was investigated for the first time at temperatures ranging from 673 to 823 K and at constant strain rates from 1 × 10−3 to 1 × 10−2 s−1. A maximum elongation of 692% was obtained at a temperature of 723 K and a strain rate of 5 × 10−3 s−1. High-strain rate superplasticity with an elongation of 371% was realized at a temperature of 723 K. It was found that the Si3N4 nanoparticles play an important role in the stability of the microstructure of the Si3N4/Ni–Co nanocomposite. The relatively large superplasticity of the nanocomposite compared to the Ni–Co alloy is discussed. Deformed microstructure, fracture and surface morphology are examined and the deformation mechanism of the composite is discussed.
13 citations
TL;DR: In this article, the cavities were arranged in a straight line parallel to the tensile axis in the centre of the sample, and a more appropriate cavity growth equation considering the critical strain was proposed to describe the cavitation behaviour.
Abstract: Cavitation behaviour has been investigated in an Al–Zn–Mg–Cu alloy with an average grain size of 10 µm during superplastic deformation. The superplastic tensile tests were interrupted at different true strains at 530°C and 3 × 10−4 s−1. The results showed that cavity nucleation occurred above a critical strain in the optimum loading condition. It was easy for cavities to form at the triple junction due to the stress concentration caused by cooperative grain boundary sliding. Since the tensile stress was higher in the middle of the sample, the cavities were arranged in a straight line parallel to the tensile axis in the centre of the sample. A more appropriate cavity growth equation considering the critical strain was proposed to describe the cavitation behaviour.
4 citations
TL;DR: In this paper, nanocomposites of Al2O3/NiCo prepared using Al 2O3 of various particle sizes were fabricated by pulse current electrodeposition, and their superplastic tensile deformation was investigated at strain rates of 833-10−4-s−1 and 167 -10−3 -s−3 1 and temperatures of 723-823 -k.
3 citations
References
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06 Nov 2008
TL;DR: A balanced mechanics-materials approach and coverage of the latest developments in biomaterials and electronic materials, the new edition of this popular text is the most thorough and modern book available for upper-level undergraduate courses on the mechanical behavior of materials as discussed by the authors.
Abstract: A balanced mechanics-materials approach and coverage of the latest developments in biomaterials and electronic materials, the new edition of this popular text is the most thorough and modern book available for upper-level undergraduate courses on the mechanical behavior of materials To ensure that the student gains a thorough understanding the authors present the fundamental mechanisms that operate at micro- and nano-meter level across a wide-range of materials, in a way that is mathematically simple and requires no extensive knowledge of materials This integrated approach provides a conceptual presentation that shows how the microstructure of a material controls its mechanical behavior, and this is reinforced through extensive use of micrographs and illustrations New worked examples and exercises help the student test their understanding Further resources for this title, including lecture slides of select illustrations and solutions for exercises, are available online at wwwcambridgeorg/97800521866758
2,905 citations
Journal Article•
TL;DR: A general survey of plastic deformation can be found in this article, where Orowan and Bailey-Orowan equations are used to define deformation mechanism maps for pure metals.
Abstract: 1. Deformation and Creep. Deformation. Definition of creep. Time dependence of creep strain. Creep Curve. Mechanisms of plastic deformation: A general survey. Mechanical equation of state. Creep test compared with tensile test at constant strain rate and constant loading rate. Creep tests at constant load and constant stress. 2. Motion of Dislocations. Dynamic Recovery. Motion of dislocations. Free, mobile and moving dislocations. Dynamic recovery. 3. Temperature Dependence of Creep Rate. Activation energy of creep. Methods of determination of activation energy of creep. Correction of experimentally determined activation energy of creep for temperature dependence of elastic modulus. Activation energy or creep and activation enthalpy of diffusion. 4. Applied Stress Dependence of Creep Rate. Initial creep rate. Steady-state creep. Transient creep. 5. Influence of Grain Size and Stacking Fault Energy. Grain size. Stacking fault energy. 6. Orowan and Bailey-Orowan Equations. Orowan equation. Bailey-Orowan equation. Relation between Orowan equation and Bailey-Orowan equations. A consequence of the equivalence of Orowan and Bailey-Orowan equations. Experimental verification of Bailey-Orowan equation. Experimental determination of quantities r and h. Incubation period and ``Frictional'' stress. 7. Back Stress. Internal, threshold and frictional stress. Internal and effective stress. Concept of internal and effective stress and the mechanical equation of state. Definitions of experimental parameters. Interpretation of experimental parameters. 8. Dislocation Structure. Development of dislocation structure during creep. Basic quantitative characteristics of dislocation structure. Subgrain structure. Subgrain structure and long-range internal stress. Behaviour of sub-boundaries. Interaction of dislocations with sub-boundaries. Generation of dislocations. Structural steady state. Concept of hard and soft regions and measured internal stress. 9. Dislocation Creep in Pure Metals. Creep controlled by recovery. Creep controlled by dislocation glide. Models based on thermally activated glide and diffusion controlled recovery. Relation between constants A and n in the dorn creep equation and the natural third power law. Harper-Dorn creep. 10. Creep in Solid Solution Alloys. Introduction. Mechanisms of creep strengthening in solid solutions. Creep controlled by viscous dislocation glide. 11. Creep in Precipitation and Dispersion Strengthened Alloys. Models of Ansell and Weertman. Back stress concept. 12. Diffusional Creep. Nabarro-Herring and Coble creep. Subgrain boundaries as sources and sinks for vacancies. Diffusional creep and grain boundary sliding. Reactions on grain boundaries. Diffusional caritational creep. 13. Deformation Mechanism Maps. Equations used for construction of deformation mechanism maps. Examples of deformation mechanism maps. ``Generalized'' deformation mechanism map for pure metals. 14. Grain Boundary Sliding.
499 citations
TL;DR: The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitive at intermediate strain rate (region II) where the material exhibits optimal super-plasticity as discussed by the authors.
Abstract: The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitivity at intermediate strain rates (region II) where the material exhibits optimal superplasticity This relationship is examined in detail, with reference both to the conflicting results reported for the Zn-22 pct Al eutectoid alloy and to the significance of the three regions of flow
378 citations
TL;DR: In this article, the deformation behavior of a superplastic Ti-6A1-4V alloy at 927°C has been characterized by means of constant strain-rate tensile tests up to large plastic strain.
Abstract: The deformation behavior of a superplastic Ti-6A1-4V alloy at 927°C has been characterized by means of constant strain-rate tensile tests up to large plastic strain. Significant hardening has been recorded in the course of deformation. Microstructural studies on deformed samples indicate the occurrence of simultaneous strain-rate induced grain growth, which explains nearly all of the hardening. A small amount of hardening may also be expected from grain elongation or grain clustering effects. As a result of concurrent grain growth, the strain-rate sensitivity is found to decrease with strain, thus indicating that stress-strain rate behavior determined initially may not be applicable after large amounts of plastic strain. The stressJstrain-rate data obtained from step strain-rate test for a variety of grain sizes, together with the grain growth kinetics plots, provide a means for developing a constitutive description for this material at large strains.
250 citations