Cavitation behavior of an Al−Cu eutectic alloy during superplastic deformation
01 Mar 1989-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer-Verlag)-Vol. 20, Iss: 3, pp 453-462
TL;DR: In this article, the cavities were spherical in most cases, which was attributed to the diffusion-controlled cavity growth mechanism and its modification when the cavity size reaches the size of a grain.
Abstract: Cavitation behavior upon deformation of an Al−Cu eutectic alloy was studied by densitometry and quantitative microscopy. Tensile specimens were strained to different strain levels at constant strain rates and temperatures over the range of 10−5 to 10−2 s−1 and 400° to 540 °C, respectively. The cavity volume increased with increasing strain and strain rate but decreased with increasing temperature. The increase in cavity volume occurred through an increase in both the number and size of cavities. The cavities were spherical in most of the cases, which was attributed to the diffusion-controlled cavity growth mechanism and its modification when the cavity size reaches the size of a grain. The number and volume of cavities were used to evaluate the nature of the cavity nucleation rate and the level of pre-existing cavities.
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TL;DR: In this paper, the tensile ductility of superplastic ceramics and metallic alloys was investigated and the authors showed that tensile deformation is not only a function of the strain-rate-sensitivity exponent, but also a factor of the parameter ⋗e exp (Qc/RT), where Qc is the steady-state strain rate and RT is the activation energy for super-plastic flow.
Abstract: Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-rate-sensitivity exponent, m, is high (m⩾0.5). The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminium, nickel and titanium alloys) is primarily a function of the strain-rate-sensitivity exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia-alumina composites and iron carbide) is not only a function of the strain-rate-sensitivity exponent, but also a function of the parameter ⋗e exp (Qc/RT) where ⋗e is the steady-state strain rate and Qc is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase in ⋗e exp (Qc/RT). This trend in tensile elongation is explained based on a “fracture-mechanics” model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase in the parameter (2γs−γgb), where γs is the surface energy and γgb is the grain boundary energy. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramics deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.
92 citations
15 Dec 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a relatively coarse-grained AZ61 alloy deformed under two conditions for which grain-boundary sliding (GBS) creep controlled plastic flow and which produced the same flow stress of 10MPa.
Abstract: Cavitation behavior has been investigated in a relatively coarse-grained AZ61 alloy deformed under two conditions for which grain-boundary sliding (GBS) creep controls plastic flow and which produce the same flow stress of 10 MPa. At a strain rate of 10−5 s−1 and a temperature of 573 K, GBS creep is rate controlled by grain-boundary diffusion, DGB. At a strain rate of 2 × 10−4 s−1 and a temperature of 648 K, GBS creep is rate controlled by lattice diffusion, DL. Tensile elongation is slightly greater when DGB accommodates GBS deformation. Despite accommodation of GBS by different diffusion mechanisms, cavity evolution under both deformation conditions is quite similar. Cavity volume percent increases similarly with strain under both conditions, as does the radius of the largest cavities. Cavity areal number density distributions are similar between the different deformation conditions when strain is a constant. All the features observed for cavitation indicate that cavity growth is plasticity controlled under both deformation conditions. The theory of plasticity-controlled cavity growth is in very good agreement with experimental data produced for this investigation.
20 citations
TL;DR: In this article, the size, shape, and configuration of internal cavities in superplastic metals and ceramics after deformation at high temperatures were investigated using a quantitative metallographic procedure and scanning video images.
Abstract: It is now well established that cavities are often formed during superplastic deformation. However, experimental investigations suggest important differences in the nature of the cavitation in typical superplastic metals and ceramics. These differences are demonstrated with reference to a superplastic Cu-based alloy and yttria-stabilized tetragonal zirconia (Y-TZP). By using a quantitative metallographic procedure and scanning video images, measurements are presented showing the size, shape, and configuration of internal cavities in these two materials after deformation at high temperatures.
11 citations
TL;DR: In this paper, the authors investigated the rate of cavitation with superplastic strain for a super-plastic AZ61 magnesium alloy at a strain rate of 2 × 10 - 4 s - 1 and temperature of 648 K, under the conditions of which an elongation of more than 250% has been found.
Abstract: The rate of cavitation with superplastic strain was investigated for a superplastic AZ61 magnesium alloy at a strain rate of 2 × 10 - 4 s - 1 and temperature of 648 K, under the conditions of which an elongation of more than 250% has been found. Cavities initiated at grain boundaries. The cavitation showed a growth perpendicular to the applied stress direction after the initial strains. The subsequent growth and coalescence of cavities invariably leads to failure of the material. The experimental growth rates are in good agreement with the rate predicted by the plasticity-controlled growth mechanism.
8 citations
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
7 citations
References
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TL;DR: In this paper, the authors investigated intergranular and interphase cavitation in binary alpha/beta brass in tension at 600°C under conditions of superplastic deformation and found that cavities nucleate preferentially at α-β interfaces.
Abstract: Intergranular and interphase cavitation in binary alpha/beta brass has been investigated in tension at 600° C under conditions of superplastic deformation. The sites for nucleation of cavities has been studied by quantitative metallography and the cavities are observed to nucleate preferentially atα-β interfaces. The process of cavitation is associated with grain boundary sliding and cavity nucleation occurs at points of stress concentrations in the sliding interfaces. Measurements of grain and phase boundary sliding at various interfaces demonstrate that sliding occurred onα-β boundaries more readily than onα-α andβ-gb interfaces. The predominance ofα-β interface cavitation is believed to be as a result of greater sliding at theα-β boundary and of an unbalanced accommodation of sliding adjacent to this type of boundary.
57 citations
TL;DR: In this article, the texture changes can be interpreted in terms of grain boundary sliding, dislocation motion and diffusion creep in the Al-33 wt% Cu eectic alloy.
55 citations
TL;DR: In this article, a study of the superplastic behavior during tensile straining of two α/β Cu-Ni-Zn alloys (nickel silvers) was made using metallographic and density techniques.
Abstract: A study has been made of the superplastic behavior during tensile straining of two α/β Cu-Ni-Zn alloys (nickel silvers). Cavitation occurred during deformation and has been studied using metallographic and density techniques. Cavities nucleated at α/β boundaries and triple points involving two phases, and cavity growth and interlinkage led to brittle superplastic fracture. Density studies showed that the volume of cavities increased with increasing strain, but was relatively independent of strain rate and temperature. The results were consistent with a high rate of cavity nucleation in the early stages of deformation, followed by a grain boundary sliding mechanism of growth.
54 citations
TL;DR: In this article, a study of cavitation during superplastic tensile straining of two microduplex steels has been made using density measurements and quantitative optical metallography.
Abstract: A study of cavitation during superplastic tensile straining of two microduplex steels has been made using density measurements and quantitative optical metallography. The steels were of basically similar composition with the exception of a trace addition of boron made to one alloy. During deformation cavities formedα/γ boundaries and matrix-carbide interfaces; the growth and coalescence of these cavities led to failure. Density measurements showed that the extent of cavitation increased with increasing strain and decreasing strain-rate, but the level of cavitation was reduced by the presence of boron. A time dependence of overall void volume of 1.4 to 2.0 was observed. Quantitative metallographic studies of the nucleation and growth contributions to the overall rate of void formation showed that boron inhibited each of these processeS. However, both the nucleation rate and the magnitude of the time exponent of void volume increase suggested that a substantial number of voids grew from pre-existing nuclei which were probably present as non-coherent carbide-matrix interfaces.
51 citations
TL;DR: In this paper, the authors measured the rate of migration of a triple junction formed between a sub-boundary in the Al and the lamellar interface and found that the interface diffusion coefficient was 1.1 × 10 3 exp [−(23,300/ RT )] between 350 and 500°C.
45 citations