Effect of layered microstructure and its evolution on superplastic behaviour of AA 8090 Al–Li alloy
TL;DR: In this article, a tensile test of AA 8090 Al-Li Alloy was performed at 803 K by tensile testing of specimens taken from the full thickness and the near surface and midthickness layers.
Abstract: Superplastic forming grade sheets of AA 8090 Al–Li alloy were observed to contain layers of different microstructure and microtexture across the thickness cross-section. Superplastic behaviour and its relationship to the concurrent microstructural and microtextural evolution of this sheet were studied at 803 K by tensile testing of specimens taken from the full thickness and the near surface and midthickness layers. Initially, the surface layers contained nearly equiaxed and relatively coarse grains with a strong S {123}〈634〉 type texture, whereas the midthickness section had elongated fine grains and a dominant Bs {011}〈211〉 texture. The stress–strain rate (σ–e) curves exhibited minimum flow stress for the full thickness material. Varying levels of grain growth and texture weakening occurred in the above two layers, the extent of which depended on whether the layers were in separated form or as coexistents in the full thickness material. The maximum values of strain rate sensitivity index for the...
Citations
More filters
20 Jan 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, microstructures required for superplasticity were fabricated by intermittent multipass friction stir processing (FSP) in a 6mm 5086 aluminium alloy plate.
Abstract: Microstructures required for superplasticity were fabricated by intermittent multipass friction stir processing (FSP) in a 6 mm 5086 aluminium alloy plate. Two processing parameters corresponding to two different heat inputs were used. Multipass FSP created a gradient microstructure with fine and coarse grain-depth features on the processed plates. Three sheets of 1.5 mm thickness with different microstructural features were extracted for deformation testing under superplastic conditions: a layer with only fine grains from the nugget layer (NL), a layer with a thermomechanical-/heat-affected layer containing coarse grains (TL), and a composite layer (CL) having both fine and coarse grains in equal proportions. High temperature tensile testing was conducted for different layers between 450–550 °C with strain rates ranging from 5×10−4 s−1 to 1×10−2 s−1 to determine the optimum superplastic conditions. The NL and CL were comparable in terms of ductility with a high m value of 0.44. The maximum ductility values were 325% for NL, 355% for CL and 230% for TL. The high ductility of the composite layers, despite their microstructural inhomogeneity, establishes multipass FSP as an effective bulk processing technique.
38 citations
TL;DR: In this paper, the NaCl-induced hot corrosion behaviors of TiN coatings at 500˚C were investigated, and it was found that NaCl solution infiltrated into the coatings through defects, thus forming NaxTiyOz products inside the coating.
26 citations
23 Feb 2021-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
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
01 Jan 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the influence of heat treatments on microstructure and creep behavior of hot-rolled (HR) Ti-6Al-4V alloy was investigated, and it was shown that the microstructures of HR alloy consists of needle-like β phase distributed within stripe-like α phase.
Abstract: The influence of heat treatments on microstructure and creep behavior of hot rolled (HR) Ti–6Al–4V alloy is investigated. Results show that the microstructure of HR alloy consists of needle-like β phase distributed within stripe-like α phase. After long term aging (LTA), significant amount of particle-like β phase precipitates within α phase. After solution treatment at 940 °C and aging, the microstructure of the alloy consists of the “basket weave” structure with high volume fraction and the equiaxed α phase. Under the condition of the applied stress of 575 MPa at 400 °C, creep lifetimes of HR alloy treated by long term aging and solution treatment at 940 °C increase from 72 h to 230 h and 548 h, respectively. During the creep, deformation mechanism of HR alloy solution treated at 940 °C is significant amount of 〈 a + c 〉 dislocations with wave-like feature activated on pyramidal plane of α phase. Deformation mechanism of HR–LTA alloy is the slip of 〈 c 〉 dislocation with hook-like feature activated on cylindrical plane of α phase, and dense dislocations may be concentrated to form the subgrains due to the occurrence of dynamic recrystallization.
16 citations
25 Jun 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of local strain developed on the microstructural variation along the gauge length of tensile specimens was studied and a model was proposed for cavity nucleation on the basis of inhomogeneity in microstructure and its implication in deformation mechanism.
Abstract: Superplastic deformation of Al–Li 8090 alloy was carried out to study the effect of local strain developed on the microstructural variation along the gauge length of tensile specimens. For this, separate specimens were deformed to failure at a constant temperature of 530 °C and at the strain rates within the superplastic regime. The strain distribution was found to be non-uniform with more deformation towards fracture tip and less towards the shoulder section of specimens. The grain size was found to decrease with increase in local strain whereas cavity size and cavity volume fraction were found to increase. The cavity growth in longitudinal direction is suggested to be controlled by power law but the same in transverse direction is controlled by diffusional process. A model is proposed for cavity nucleation on the basis of inhomogeneity in microstructure and its implication in deformation mechanism.
15 citations
References
More filters
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: 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
TL;DR: In this paper, the deformation of AA8090 Al-Li-Mg-Cu-Zr alloy at elevated temperature and slow strain rates has been investigated in uniaxial tension.
Abstract: The deformation of AA8090 Al-Li-Mg-Cu-Zr alloy at elevated temperature and slow strain rates has been investigated in uniaxial tension. Under suitable conditions, this material exhibited a high strain-rate sensitivity of the flow stress and was superplastic. This superplastic behavior was obtained in material with an initially elongated grain structure combined with a distribution of similarly oriented grains and low-angle grain boundaries that was not conducive to boundary sliding. Observations of the development of microstructure and of the crystallographic preferred orientation indicated that no significant rigid body translation and little rotation of grain interiors occurred up to strains of about 0.4 and that the probability of relative translation of grain interiors up to strains of at least 1 was low. The changes of structure observed could be accounted for by a combination of grain growth and grain rotation. The consequence of these observations on the grain switching and grain boundary sliding mechanisms generally assumed to operate during superplastic deformation is discussed, with the conclusion that those mechanisms may not be wholly appropriate for explaining high rate sensitivity in this material over the range of strain rates investigated.
33 citations
TL;DR: In this article, the plastic anisotropy of AA8090 Al-Li-Cu-Mg alloy sheet has been evaluated by tensile testing and by deep drawing at temperatures in the range 200 °C to 525 °C.
Abstract: The plastic anisotropy of AA8090 Al-Li-Cu-Mg alloy sheet has been evaluated by tensile testing and by deep drawing at temperatures in the range 200 °C to 525 °C. At temperatures of about 500 °C and strain rates of about 10-3 s-1, this material exhibits a high strain-rate sensitivity of flow stress which reduces any tendency to strain localization in stretching and allows so-called superplastic forming of the sheet. Most models of the material behavior in this regime require highly inhomogeneous deformation on the scale of the material’s grain size. The plastic anisotropy measured in the superplastic regime was similar in form, though of reduced magnitude, to that measured under conditions associated with a much smaller strain-rate sensitivity. Homogeneous slip models predict the correct form of anisotropy, and inclusion of slip-rate senitivity can reduce the magnitude of anisotropy predicted but not sufficiently to give good correlation with the experimental results unless very high values are used. The development of the preferred crystallographic orientation in deep drawing has also been examined. The predictions of homogeneous slip models correlate quite well with experimental results at low temperatures, but the situation is more complex in the superplastic regime where, although there is some evidence of texture changes as predicted, there is a general reduction in the intensity of preferred orientation with deformation. However, the results indicate that a greater contribution of homoeneous slip deformation is involved in superplastic deformation than is assumed in some models of superplasticity.
19 citations
TL;DR: In this article, the development of texture and microstructure in a thermomechanically processed quaternary Al-Li-Cu-Mg alloy was investigated using optical microscopy and transmission electron microscopy.
Abstract: The development of texture and microstructure in a thermomechanically processed quaternary Al-Li-Cu-Mg alloy has been investigated. Textures on both the surface (1/8 thickness (T)) and midthickness levels of specimens were measured using the conventional pole figure as well as the orientation distribution function (ODF) method. Microstructural characterization was carried out with the help of optical microscopy and transmission electron microscopy (TEM). The processing schedule involved hot cross rolling, followed by several stages of cold rolling (CR) with intermediate solution treatments (STs). A marked through-thickness texture inhomogeneity developed in the processed sheets during the course of thermo mechanical treatment (TMT). In general, the texture produced at the midthickness level was 2 to 3 times sharper than the texture at the surface.
15 citations