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Journal ArticleDOI

Effects of strain rate and test temperature on flow behaviour and microstructural evolution in AA 8090 Al–Li alloy

01 Apr 2001-Materials Science and Technology (Taylor & Francis)-Vol. 17, Iss: 4, pp 431-438
TL;DR: In this paper, tensile specimens of superplastic forming grade AA 8090 Al-Li alloy were deformed at constant strain rates in the range 1×10-5 −1×10 −2 s −1 and at constant temperatures in the ranges 298 −843 K, to investigate their effects on the nature of stress-strain (cσ-e curves and on the concurrent microstructures, substructures, and microtextures.
Abstract: Tensile specimens of superplastic forming grade AA 8090 Al–Li alloy were deformed at constant strain rates in the range 1×10-5–1×10-2 s-1 and at constant temperatures in the range 298–843 K, to investigate their effects on the nature of stress–strain (cσ–e curves and on the concurrent microstructures, substructures, and microtextures. The σ–e curves exhibited flow hardening in the early part of deformation, the rate of which was found to increase with an increase in strain rate and decrease in temperature. Grain growth, cavitation, dislocation interactions, and texture weakening were observed to occur during superplastic deformation. The early part of deformation involved a substantial dislocation slip contribution to flow hardening and to the mechanism for superplastic flow. However, the microstructural evolution facilitated the conventional mechanism of grain boundary sliding and its accommodation by the diffusional process, as suggested by the strain rate sensitivity index and activation energy...
Citations
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Journal ArticleDOI
TL;DR: In this paper, the development history and applications of Al-Li alloys over the last few years are reviewed, and the main issue of anisotropic behavior of all the alloys is discussed.

360 citations

Journal ArticleDOI
TL;DR: In this article, the strain rate sensitivity of thermoplastic materials namely high density polyethylene (HDPE), homopolymer polypropylene, and high isotactic homopolymers polypropane and concurrent microstructural evolution is investigated.
Abstract: The strain rate sensitivity of thermoplastic materials namely high density polyethylene (HDPE), homopolymer polypropylene, and high isotactic homopolymer polypropylene and concurrent microstructural evolution is investigated. Strain rate sensitivity index followed the sequence, HDPE>homopolymer polypropylene>high isotactic homopolymer polypropylene. The strain rate sensitivity index parameter of the examined polymeric materials is consistent with the micro-mechanisms of deformation and modes of fracture. Deformation processes in HDPE involved fibrillation and craze-tearing, while homopolymer polypropylene and high isotactic polypropylene were predominantly characterized by craze-tearing and brittle modes of fracture.

94 citations

Journal ArticleDOI
TL;DR: In this paper, the response of neat high isotactic polypropylene and talc (iPP-T) and wollastonite reinforced polypropylenes to tensile loading rate and the evolution of microstructure during plastic deformation was described.
Abstract: The paper describes the response of neat high isotactic polypropylene (iPP) and talc (iPP-T) and wollastonite (iPP-W)-reinforced polypropylenes to tensile loading rate and the evolution of microstructure during plastic deformation. Unreinforced and reinforced polypropylene materials exhibit significant sensitivity to tensile loading rate (strain rate) and the change in strain rate sensitivity index parameter with strain signifies a change in the micromechanism of plastic deformation and mode of fracture. Plastic deformation in neat high isotactic polypropylene is characterized by craze-tearing and brittle mode of fracture, while both talc- and wollastonite-reinforced polypropylenes are characterized by wedge, ridge-tearing, fibrillation, and brittle fracture. The brittle fracture is associated with debonding of mineral particles from the polypropylene matrix. However, yield stress of all the three materials exhibit similar dependence to loading rate and similar activation volume that suggests similarity in the onset of plastic deformation process.

57 citations

Journal ArticleDOI
TL;DR: In this article, the strain rate sensitivity of neat polypropylene and wollastonite-mineral filled polypolypropylene (PP-W) and concurrent microstructural evolution is investigated.
Abstract: The strain rate sensitivity of neat polypropylene (PP) and wollastonite-mineral filled polypropylene (PP-W) and concurrent microstructural evolution is investigated. Both the materials are strain rate sensitive and the change in strain rate sensitivity index parameter with strain reflects the change in micromechanisms of deformation and modes of fracture. Deformation processes in neat polypropylene involved craze-tearing and brittle mode of fracture, while wollastonite-filled polypropylene composite was predominantly characterized by wedge, ridge-tearing, fibrillation and brittle fracture. The dependence of yield stress of neat polypropylene (PP) and wollastonite-filled polypropylene (PP-W) with strain rate follows Eyring’s equation and yield similar activation volume implying similarity in the onset of plastic deformation.

44 citations

Journal ArticleDOI
TL;DR: In this paper, a novel Al-3.9Zn-4.25Zr alloy is employed to determine what effects the testing conditions, elemental and phase composition and evolution of grain and sub-grain structure make towards deformation mechanisms.
Abstract: The role of different deformation mechanisms and the contributing factors behind them needs to be clearly defined to develop materials exhibiting high strain rate superplasticity. It is still not fully understood to what extent the deformation conditions and microstructural parameters affect the mechanisms of superplastic deformation. A novel Al–3.9Zn–4.1Mg–0.8Cu–2.8Ni–0.25Zr alloy is employed to determine what effects the testing conditions, elemental and phase composition and evolution of grain and sub-grain structure make towards deformation mechanisms. To analyze the deformation behavior and microstructure evolution, uniaxial tensile tests are performed following two deformation regimes with the different constant strain rates and temperatures: (1) 2 × 10-3 s-1, 480°С and (2) 2 × 10-2 s-1, 440°С. The elongation to failure exceeds 650% and the strain rate sensitivity coefficient m is near 0.5 at both deformation regimes. Electron microscopy and focused ion beam techniques are employed to analyze mechanisms associated with grain boundary sliding and intragranular strain by using the samples in a stable flow. Surface grids indicated that superplastic flow is accompanied by the formation of striated regions on the surface, whereas grain boundary sliding involves grain neighbor switching and grain rotation. Intragranular deformation with increased dislocation density and dynamic recrystallization are also observed. Weaker intergranular and intense intragranular deformation are revealed at high strain rate deformation regime. Solute effect and the presence of two types of secondary phases, nanoprecipitates of L12-Al3Zr and micron-sized eutectic Al3Ni, are discussed in comparison to conventional AA7475 alloy in different aspects of grain growth, dynamic recrystallization and strain-rate sensitivity.

30 citations

References
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Book
01 Jan 1972
TL;DR: Physical Metallurgy Principles as mentioned in this paper is intended for use in an introductory course in physical metallurgy and is designed for all engineering students at the junior or senior level and is largely theoretical, but covers all aspects of physical metelurgy and behavior of metals and alloys.
Abstract: Physical Metallurgy Principles is intended for use in an introductory course in physical metallurgy and is designed for all engineering students at the junior or senior level. The approach is largely theoretical, but covers all aspects of physical metallurgy and behavior of metals and alloys. The treatment used in this textbook is in harmony with a more fundamental approach to engineering education.

2,265 citations

Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: In this paper, texture development during the thermomechanical processing of high strength aluminium alloys is reviewed and the implications of texture development are considered by examining the effects that texture can have on tensile property anisotropy and fatigue and fracture behaviour.
Abstract: Texture development during the thermomechanical processing of high strength aluminium alloys is reviewed. The alloys dealt with include both conventional heat treatable alloys, and unconventional materials such as rapidly quenched alloys and metal-matrix composites. The processing routes considered include hot and cold rolling, extrusion, forging, recrystallisation, and superplastic deformation. The information is presented as (111) pole figures and orientation distribution functions, in order to illustrate the much greater degree of detailed information that can be extracted from the latter method of analysis. The implications of texture development are considered by examining the effects that texture can have on tensile property anisotropy and fatigue and fracture behaviour.MST/1292

61 citations

Journal ArticleDOI
TL;DR: In this paper, the tensile behavior and deformation mechanisms of the 8090 Al-Li alloys were investigated and analyzed over the strain rates range 10−5 to 10−2 s−1.
Abstract: The 8090 Al-Li alloys, after a special thermomechanical process (TMP), exhibited low-temperature superplasticity (LTSP) from 350 °C to 450 °C and behaved differently from the conventional high-temperature superplasticity (HTSP). The LTSP sheets after ~700 pct elongation at 350 °C and 8 × 10−4 s−1 still possessed fine “(sub)grains” 3.7 μm in size and narrow surface Li-depletion zones 11 μm in width, resulting in a post-SP T6 strength of ~500 MPa, significantly higher than that of the 8090 alloys tested at normal superplastic temperature of 525 °C or above. Examination from the movement of surface marker lines in LTSP samples confirmed the role of grain boundary sliding (GBS), coupled with grain rotation and migration. During the initial stage (<150 pct), GBS along certain higher-angled boundaries was proceeded along a plane ±45 deg with respect to the sample surface. With increasing straining, sliding between individual grains or grain groups was observed on other planes, forming a zigzag morphology. Transmission electron microscopy (TEM) observations revealed appreciable dislocation activities, suggesting the involvement of dislocation creep. The tensile behavior and deformation mechanisms of the HTSP and LTSP sheets were investigated and analyzed over the strain rates range 10−5 to 10−2 s−1. The strain-rate sensitivity(m value) for the LTSP and HTSP materials was found to be ~0.33 and 0.50, respectively. The activation energy was extracted to be 92 kJ/mole for the LTSP sheets and to be 141 kJ/mole for the HTSP sheets. Based upon these results, the primary deformation and accommodation mechanisms for the HTSP and LTSP sheets are GBS and dislocation creep, respectively.

54 citations