Grain growth behaviour of the Al-Cu eutectic alloy during superplastic deformation
01 Sep 1991-Journal of Materials Science (Kluwer Academic Publishers-Plenum Publishers)-Vol. 26, Iss: 17, pp 4657-4662
TL;DR: Grain growth behavior of the Al-Cu eutectic alloy was investigated as a function of strain (e), strain rate and deformation temperature (T) over as discussed by the authors, where grain size increases with increase in strain and temperature.
Abstract: Grain growth behaviour of the Al-Cu eutectic alloy was investigated as a function of strain (e), strain rate
$$(\dot \varepsilon )$$
and deformation temperature (T) over
$$\dot \varepsilon $$
= 10−2 s−1 and T=400 to 540°C The grain size increases with increase in strain and temperature Upon deformation to a fixed strain, the grain growth is generally seen to be more at lower strain rates The rates of overall grain growth
$$(\dot d_{\varepsilon ,t} )$$
and due to deformation alone
$$(\dot d_\varepsilon )$$
, however, increase with increasing strain rate according to
$$\dot d_{\varepsilon ,t} \propto \dot \varepsilon ^{086} $$
and
$$\dot d_{\varepsilon ,t} \propto \dot \varepsilon ^{064} $$
, respectively The increase in the grain growth rate with strain rate is attributed primarily to the shorter time involved at higher strain rate for reaching a fixed strain The activation energy for grain growth under superplastic conditions is estimated to be 79 kJ mol−1
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TL;DR: In this article, the role of grain boundary sliding (GBS), intragranular deformation and the change of microstructure during superplastic deformation have been investigated for ultrafine-grained Al-Mg alloy with a grain size of less than 1 μm using Multi-Axial Alternative Forging (MAF) technique.
Abstract: In practical application, an appearance of low temperature superplasticity (LSTP) is one of necessaries conditions. In this paper, to estimate an appearance and deformation mechanisms of this superplasticity, the role of grain boundary sliding (GBS), intragranular deformation and the change of microstructure during superplastic deformation have been investigated for ultrafine-grained Al-Mg alloy with a grain size of less than 1 μm using Multi-Axial Alternative Forging (MAF) technique. In these materials, it shows that the elongation and strain rate sensitivity (m-value) were 340% and 0.39, respectively, at 473 K under a strain rate of 2.8 x 10 -3 s -1 . These results show that superplastic appearance is possible at 473 K. The void formed at 473 K elongated in parallel to the tensile direction, with a length of 15 μm and a width of 5 μm. The intragranular deformation contribution was estimated from the aspect ratio of the grains after deformation and its contribution ratio was about 33.5 %. Therefore, for the appearance of lower temperature superplasticity with large elongation and m-value, the role of intragranular deformation was the most important factor together with GBS under these conditions. As described above, the MAF technique is one of the most effective methods to produce ultrafine-grained material and appearance of lower temperature superplasticity.
49 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
01 Jun 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the superplastic behavior of an Al-12.7mass%Si−0.7 mass%Mg alloy was investigated under different conditions and a maximum elongation to failure of 379% was demonstrated with a strain rate sensitivity, m, of 0.52 and an activation energy for flow, Q, of 156.7 KJ/mol at 793 K at an initial strain rate of 1.67×10 −4 ǫs −1, which is close to the lattice diffusion activation energy of aluminum.
Abstract: The superplastic behavior of an Al–12.7mass%Si–0.7mass%Mg alloy was investigated under different conditions. Reasonable superplastic elongations were achieved in the fine-grained (9.1 μm) Al–Si–Mg alloy at temperatures ranging from 733 to 793 K at initial strain rates ranging from 1.67×10 –4 to 1.67×10 –3 s −1 . A maximum elongation to failure of 379% was demonstrated with a strain rate sensitivity, m , of 0.52 and an activation energy for flow, Q , of 156.7 KJ/mol at 793 K at an initial strain rate of 1.67×10 –4 s −1 , which is close to the lattice diffusion activation energy of aluminum. The dislocation activity within Al grains indicated that intragranular slip is the accommodation mechanism of grain boundary sliding. EBSD (Electron Backscatter Diffraction) results revealed that most grain boundaries were high angle boundaries and therefore indicated that boundary sliding and grain rotation occurred during deformation. A deformation mechanism map was plotted for the Al–Si–Mg alloy at 793 K and it is shown that the experimental datum points are in excellent agreement with the predictions of the map. Most cavities were formed around silicon particles and the cavity formation mechanism was proposed. The observation on the fracture surface revealed the presence of filaments. The filament quantity or density increased with increasing testing temperature, which can be interpreted by the transition of dislocation viscous glide creep to grain boundary sliding mechanism at elevated temperatures. The formation of filaments was related to the deformation mechanisms and the lattice diffusion at elevated temperatures. The superplastic fracture in the Al–Si–Mg alloy exhibited a diffuse necking and was a pseudo-brittle fracture. The fracture mechanism was intergranular fracture.
27 citations
TL;DR: Of a particular interest are results related to behaviour of CuAl2 in superplastic Al‐33wt%Cu during deformation, including several problems with the use of EBSD in this alloy.
Abstract: The effect of hot deformation on fully recrystallized aluminium-copper alloys (Al-4wt%Cu and Al-33wt%Cu) with different volume fractions of CuAl(2) has been studied. The alloys are Zener pinned systems with different superplastic properties. Strain-induced grain growth, observed in both alloys, was quantitatively estimated by means of electron microscopy and EBSD and compared with the rate of static grain growth. Surface marker observations and in situ hot-deformation experiments combined with EBSD were aimed at clarifying the mechanisms responsible for the changes in the deformed microstructures. A sequence of secondary and backscattered electron images and EBSD maps was obtained during in situ SEM deformation with different testing conditions. Overlaying EBSD maps for the Al-4wt%Cu with channelling contrast images showed that grain boundary motion occurred during deformation, creating a layered structure and leading to an increase in size of some grains and shrinkage of others. Of a particular interest are results related to behaviour of CuAl(2) in superplastic Al-33wt%Cu during deformation, including several problems with the use of EBSD in this alloy.
16 citations
Cites background from "Grain growth behaviour of the Al-Cu..."
...early works on superplasticity (Stowell et al., 1969; Kashyap, 1991) reported an increase in the average grain size in this alloy during deformation; however, all measurements were performed manually and often without distinguishing between the two phases....
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...…Journal compilation C© 2009 The Royal Microscopical Society, Journal of Microscopy, 233, 432–441 early works on superplasticity (Stowell et al., 1969; Kashyap, 1991) reported an increase in the average grain size in this alloy during deformation; however, all measurements were performed manually…...
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02 Jan 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of hydrogen on high temperature flow behavior of VT20, a near α-Ti alloy, was studied using differential strain rate compression tests, and the results indicated that the deformation mechanism is the grain boundary sliding accommodated by lattice diffusion.
Abstract: The effect of hydrogen on high temperature flow behavior of VT20, a near α-Ti alloy, was studied using differential strain rate compression tests. Hydrogen level was varied from 0.0015 to 0.36 wt%. Strain rate jump tests were carried out over the strain rate and temperature ranges of 10−3–10−1 s−1 and 600–947 °C, respectively. The addition of hydrogen increased the volume fraction of β phase, decreased the grain size and lowered the flow stress up to test temperature of 900 °C. The values of apparent strain rate sensitivity (m) and activation energy for deformation (Q) were found to vary from 0.03 to 0.46 and 176–382 kJ/mol, respectively, depending on strain rate, test temperature and hydrogen level. With increasing hydrogen content the peak strain rate sensitivity shifted to lower temperatures. The values obtained for m (≥0.30) and Q (~176 kJ/mol) suggested that the deformation mechanism is the grain boundary sliding accommodated by lattice diffusion. The lower values of m (0.20–0.25) suggested dislocation climb as the deformation mechanism and the further decrease in m and increase in Q suggested power law breakdown.
12 citations
References
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TL;DR: In this paper, it was shown that the stress-strain curves rapidly attain a steady-state value at strain rates below ′10-4 s-1, and there is a sigmoidal relationship between stress and strain rate which may be obtained using several different testing procedures.
Abstract: Experiments were conducted to determine the mechanical properties of the superplastic Al-33 Pct Cu eutectic alloy at temperatures from 673 to 723 K. Specimens were tested in a well-annealed condition and there was no evidence for grain growth even at the lowest experimental strain rate of 6.7 × 1(10-7 s-1. It is shown that the stress-strain curves rapidly attain a steady-state value at strain rates below ′10-4 s-1, and there is a sigmoidal relationship between stress and strain rate which may be obtained using several different testing procedures. The maximum elongation to failure recorded in these experiments was 1475 Pct at an initial strain rate of 1.3 × 10-5 s-1. The true activation energy for plastic flow is 175 ±11 kJ mol-1 in the superplastic region II, but it increases to 299 ± 18 kJ mol-1 at low strain rates in region I. The exponent of the inverse grain size is 2.1 ±0.3 in region II. These results show that, when the grains size is stable, there is a genuine region I in the Al-33 Pct Cu alloy at initial strain rates below ∼10-5 s-1.
28 citations
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
26 citations
TL;DR: In this paper, a microduplex stainless steel was investigated to examine grain growth during static annealing and superplastic deformation at 1000° C. The grain size at a constant strain rate of 1×10−4 sec−1 increases according to d∼8t 0.19e0.49 where d is the grain size and t is the time involved in deformation.
Abstract: A microduplex stainless steel (25.7 wt% Cr-6.6 wt% Ni) was investigated to examine grain growth during static annealing and superplastic deformation at 1000° C. The grain size at a constant strain rate of 1×10−4 sec−1 increases according to d∼8t
0.49 where d is the grain size and t is the time (in min) involved in deformation. Under the present test condition, the contribution of both static (time, t
S) and dynamic (strain, e) annealing appear to be significant and can be expressed by d∞
0.19e0.29. While the exponent of the first term is constant, the exponent of the second term may depend on the strain rate. Strain rate sensitivities were evaluated from differential strain rate tests for different initial grain sizes. Both strain rate sensitivity and grain size were noticed to increase with deformation.
22 citations
TL;DR: In this paper, the compressive response of superplastic Al-CuAl2 eutectic alloy has been experimentally evaluated and it was concluded that the super-plastic al-cuAl2 is isotropic in its response to compressive forces.
Abstract: The compressive response of superplastic Al-CuAl2 eutectic alloy has been experimentally evaluated. The deformation is viscous and requires an initial time interval for the onset of steady-state deformation. At all test temperatures the strain at which the steady state is reached is an increasing function of the strain rate. In the steady-state region, the observed stress is a linear function of the diameter-to-height ratio, d/h, so long as d/h is less than or approximately equal to 2.0. When d/h is >2.0, end effects introduce nonlinearity. Basic curves derived in compression agree very well with earlier results in tension. Activation-energy values are also reported and their equivocal nature explained. It is concluded that the superplastic Al-CuAl2 eutectic alloy is isotropic in its response to compressive forces. Additional experiments reveal that the purity of raw materials does not have a significant effect on behaviour during superplastic compression.
17 citations
TL;DR: In this paper, the authors define a vitesse de deformation differentielle entre 440 and 540 C. La sensibilite a la vitez de deformations pendant la deformation superplastique est de 0,59, elle ne depend pas de maniere significative de la temperature.
16 citations