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Journal ArticleDOI

Microtextural evolution during superplastic deformation of AA 8090 Al–Li alloy

01 Mar 2001-Materials Science and Technology (Taylor & Francis)-Vol. 17, Iss: 3, pp 237-248
TL;DR: In this article, the results of a microtextural evolution study on AA 8090 Al-Li alloy were presented, showing that the surface layer was dominated by S {011}〈634〉 type texture, whereas the mid-thickness layer dominated by brass {011]〈211-type texture.
Abstract: A brief review of orientation imaging microscopy and an overview of the results of investigations related to textural evolution during superplastic deformation of a recent series of superplastic grade aluminium alloys, and specifically the results of the authors' study on microtextural evolution in AA 8090 Al–Li alloy, are presented. It was observed that the surface layer of the AA 8090 alloy sheet was dominated by S {011}〈634〉 type texture, whereas the midthickness layer was dominated by brass {011}〈211〉 type texture. In the course of superplastic deformation, textural weakening occurred, the rate and extent of which were different in the surface and centre regions, depending upon whether the two layers were deformed separately or as a composite in the full thickness tensile specimen. Textural weakening was generally more extensive at higher test temperatures and lower strain rates. Based on textural evolution and the presence of a large proportion of low angle boundaries, and their near eliminat...
Citations
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Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution during tensile deformation of an AZ31 alloy with grain size ranging from 17 to 40 µm, at intermediate temperatures, has been studied using electron backscattered diffraction (EBSD) and optical microscopy (OM) as the main characterization tools.
Abstract: The microstructural evolution during tensile deformation of an AZ31 alloy with grain size ranging from 17 to 40 µm, at intermediate temperatures, has been studied using electron backscattered diffraction (EBSD) and optical microscopy (OM) as the main characterization tools. Two deformation regimes could be distinguished. In the high-strain-rate regime, the stress exponent was found to be about 6, and the activation energy is close to that for Mg self-diffusion. These values are indicative of climb-controlled creep. In the lower strain rate range, elongations higher than 300 pct were measured. In this range, significant dynamic grain growth takes place during the test, and thus, the predominant deformation mechanisms have been investigated by means of strain-rate-change tests. It was found that the stress exponent varied during the test between 1.7 and 2.5, while the activation energy remains close to that for grain-boundary diffusion. The EBSD analysis revealed, additionally, the appearance of low to moderately misoriented boundaries that tend to lay perpendicular to the tensile axis. The enhanced ductility of this AZ31 alloy in this regime is attributed to the operation of a sequence of deformation mechanisms. Initially, grain-boundary sliding governs deformation; once dynamic grain growth occurs, dislocation slip becomes gradually more important. Dislocation interaction gives rise to the appearance of new interfaces by continuous dynamic recrystallization (CDRX).

151 citations

Journal ArticleDOI
TL;DR: In this paper, the hot deformation behavior of spray formed HIPed Al-Li (UL40) alloy was studied using processing map technique, where the map has been interpreted in terms of the microstructural processes occurring in situ with deformation, based on the values of a dimensionless parameter η which is an efficiency index of energy dissipation through micro structural processes.

54 citations

Journal ArticleDOI
M. Geetha1, U. Kamachi Mudali1, N. D. Pandey1, R. Asokamani1, Baldev Raj1 
TL;DR: In this paper, the microstructure, hardness, surface roughness, phases formed and corrosion behaviour of laser nitrided Ti-13Nb-13Zr biomedical alloy were reported.
Abstract: The present paper reports on the microstructure, hardness, surface roughness, phases formed and corrosion behaviour of laser nitrided Ti-13Nb-13Zr biomedical alloy. Surface melting and nitriding of the alloy were carried out using a Nd:YAG laser in pulsed mode under dilute and pure nitrogen environments. Laser nitriding of the alloy resulted in a hardness of 1600 HV and 650 HV, respectively, for pure N2 and dilute N2+ Ar environments. Cracks were not observed either on the surface or in the vertical cross-section of the samples nitrided in both environments. X-ray diffraction analysis of the sample nitrided in a pure nitrogen environment confirmed the formation of TiN, TiN0.3, alpha and beta phases along with ZrN. Quantitative analysis using electron probe microanalysis (EPMA) showed the enrichment of Zr and Ti in the dendrites. Corrosion resistance of the laser nitrided samples in a simulated body environment (Ringer's solution) was evaluated using the potentiodynamic polarisation method, and was...

40 citations

Journal ArticleDOI
TL;DR: In this paper, the superplastic deformation behaviors and the evolution processes of the microstructures of an Al-Mg-Li alloy with initial banded grains were studied by means of SEM, EBSD, TEM and FIB techniques.
Abstract: The superplastic deformation behaviors and the evolution processes of the microstructures of an Al–Mg–Li alloy with initial banded grains were studied by means of SEM, EBSD, TEM and FIB techniques. Furthermore, the contribution of GBS and IDS of true strain from 0.21 to 0.74 was quantitatively calculated. The results showed that during the stretching process, the initial banded grains were transformed into equiaxed grains, accompanied by dynamic recrystallization. Dynamic recrystallization refined the grain size, increased the high-angle grain boundaries and reduced the texture. The true stress-strain curve showed work hardening and strain softening. At the initial stage of superplastic deformation, dislocations accumulated obviously, which counteracted the softening effect caused by dynamic recrystallization. Moreover, in this stage, the IDS was the dominant deformation mechanism, with a maximum contribution of 62.3%. In the strain softening stage, the change of m value showed that GBS was the dominant deformation mechanism, and DC and IDS were accommodation mechanisms.

18 citations

Journal ArticleDOI
Xinming Zhang1, Lingying Ye1, Ying-wei Liu1, Yu-xuan Du1, Zhi-hui Luo1 
TL;DR: In this paper, the formation mechanism of the gradient particles was discussed and the results showed that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer(SL) are distributed homogeneously, whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction, and the volume fraction of the particles of the SL is higher than that in the CL.
Abstract: Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization. The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness. The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffractometry(XRD). The formation mechanism of the gradient particles was discussed. The results show that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer(SL) are distributed homogeneously, whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction, and the volume fraction of the particles in the SL is higher than that in the CL. Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL, which is the main reason for the formation of layered grain structure along the thickness in the sheets.

12 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a new microscopy called orientation imaging microscopy is described, which is based on precise measurements of local lattice orientation facilitated by backscattered Kikuchi diffraction.
Abstract: A new microscopy, called orientation imaging microscopy, is described. Imaging results from precise measurements of local lattice orientation facilitated by backscattered Kikuchi diffraction. The hardware configuration of the microscope is described, and a formal description of image formation is developed. Application of the method to several cubic materials and material conditions is described. Emphasis is given to those areas of application where new insight into polycrystalline microstructures has begun to emerge.

851 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: In this paper, an effective fully automated technique for determining crystallographic orientation from electron backscatter diffraction patterns (EBSPs) is described, where the most probable orientation is then found using the angles between the detected bands.
Abstract: The ability to measure lattice orientation in individual crystallites enables a more complete characterization of microstructure by combining lattice orientation with morphological features. Lattice orientation can be obtained by analyzing electron backscatter diffraction patterns (EBSPs). However, current computer-aided EBSP analysis techniques make it impractical to obtain the number of measurements needed for statistically reliable characterizations of microstructure. An effective fully automated technique for determining crystallographic orientation from EBSPs is described. Bands are identified by linear regions of correlation in the image intensity gradient direction. The most probable orientation is then found using the angles between the detected bands. The reliability of the technique was tested using a set of 1000 patterns obtained from annealed oxygen-free electrical grade (OFEC) copper. The orientation of each test pattern found using automatic indexing was checked against the corresponding orientation as determined by manual indexing. Ninety-nine percent of auto-indexed orientations were found to lie within 5 deg of the misorientation angle of the manual-indexed orientations. By simulating noise in the test patterns, it was found that image quality has a strong effect on the reliability of the technique. An image quality parameter is described which allows the reliability of the technique to be predicted for a pattern of given quality.

231 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: An overview of electron backscatter diffraction is presented in this paper, where experimental procedures are reviewed together with a basic theoretical description of the mechanism of pattern generation Manual and automated indexing procedures are described.
Abstract: An overview of electron backscatter diffraction is presented in which experimental procedures are reviewed together with a basic theoretical description of the mechanism of pattern generation Manual and automated indexing procedures are described The new technique of orientation imaging microscopy is presented, with examples from recrystallised AI-Mg alloy, deformed superplastic material, and fractured nickel base alloy

106 citations