Characteristics of superplasticity domain in the processing map for hot working of an Al alloy 2014---20vol.%Al2O3 metal matrix composite
20 Dec 1994-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing (Elsevier science)-Vol. 189, pp 137-145
TL;DR: In this paper, a hot working of Al alloy 2014-20vol.% Al2O3 particulate-reinforced cast-plus-extruded composite material has been generated covering the temperature range 300-500 degrees C and the strain rate range 0.001-10 s−1.
Abstract: The processing map for hot working of Al alloy 2014-20vol.%Al2O3 particulate-reinforced cast-plus-extruded composite material has been generated covering the temperature range 300-500 degrees C and the strain rate range 0.001-10 s(-1) based on the dynamic materials model. The efficiency eta of power dissipation given by 2m/(m + 1), where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of superplasticity has been identified, with a peak efficiency of 62% occurring at 500 degrees C and 0.001 s(-1). The characteristics of this domain have been studied with the help of microstructural evaluation and hot-ductility measurements. Microstructural instability is predicted at higher strain rates above (ls(-1)) and lower temperatures (less than 350 degrees C).
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TL;DR: In this article, the thermomechanical response of a blended powder metallurgy route was studied with isothermal constant strain-rate hot compression tests in the temperature range 850°C to 1200°C and strain rate range 10−3 to 10s−1.
Abstract: The thermomechanical response of Ti−6A1−4V modified with 29 pct B produced by a blended powder metallurgy route was studied with isothermal constant strain-rate hot compression tests in the temperature range 850°C to 1200°C and strain rate range 10−3 to 10s−1 Detailed analyses of the flow stress data were conducted to identify various microstructural deformation and damage mechanisms during hot working by applying available materials modeling techniques In the α+β phase field, cavitation at the matrix/TiB interfaces and TiB particle fracture occurs at low strain rates (<10−1 s−1), while adiabatic shear banding also occurs at high strain rates At low strain rates, the β phase deforms superplastically due to the stabilization of a fine grain size by the TiB particles Grain boundary and matrix/TiB interface sliding with simultaneous diffusional accommodation are observed to contribute to the β superplasticity The deformation behavior at high strain rates in the β-phase field is similar to that of the α+β phase field, with microstructural manifestations of extensive cavitation at the matrix/TiB interfaces and TiB particle fracture
9 citations
TL;DR: In this article, a simple instability condition is derived following Ziegler's continuum principles for identifying the regions of unstable metal flow during hot deformation in the processing maps, and the optimum hot working conditions are proposed from the identified stable regions (having comparatively high values of workability parameters, namely, strain rate sensitivity parameter and efficiency of power dissipation) in the developed processing maps.
Abstract: A simple instability condition is derived following Ziegler's continuum principles for identifying the regions of unstable metal flow during hot deformation in the processing maps. This criterion is examined by considering the flow stress data on 2124 Al–SiCp metal matrix composites and comparing with the microstructural observations of the deformed compression specimens in the as-vacuum hot pressed condition and vacuum hot pressed and extruded condition. The optimum hot working conditions are proposed from the identified stable regions (having comparatively high values of workability parameters, namely, strain rate sensitivity parameter and efficiency of power dissipation) in the developed processing maps.
5 citations
Cites background or methods from "Characteristics of superplasticity ..."
...Figure 2 shows the processing map for aluminium alloy AA2014–20 vol% Al2O3 generated from the ow stress data of [13] and also marked in it are the microstructures of the deformed specimens....
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...Initially, the instability condition derived in the preceding section is examined on the ow stress data of 6061 Al–10 vol% Al2O3 metal matrix composite [14]....
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...Yeh et al. [17] have conducted forging tests on 6061 Al–10 vol% Al2O3 composite in the temperature range 350–500±C with a compressive strain rate of 0.5 s¡1....
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...Figure 2 shows the processing map for aluminium alloy AA2014–20 vol% Al2O3 generated from the ow stress data of [13] and also marked in it are the microstructures of the deformed specimens....
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...Tezanos et al. [18] have examined the hot deformation behaviour of 2014 Al reinforced with 15 vol% Al2O3 particulates through forging tests at 430±C and 500±C for the strain rates of 0.5, 1.0, 1.5, 2.5 and 5 s¡1....
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17 Sep 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors present the first investigation of cracking by hot compression of any metal matrix composite in zones deforming under triaxial state of stress using synchrotron microtomography (SRμCT).
Abstract: We present the first investigation of cracking by hot compression of any metal matrix composite in zones deforming under tri-axial state of stress using synchrotron microtomography (SRμCT). The task required to reduce the unfavourable manifestations of phase contrast in the reconstructed slices is simplified by developing a Fourier domain based filter for processing of reconstructed slices. As a result for the first time an accurate characterisation of the state of 3-D damage developed by compression at 500 °C and 1 s−1 to strains of ~1 is achieved in the bulge region of a hot worked SiCP/A6061 composite. The composition of the damage is found to predominately consist of acicular shaped large to very large pores and “coalesced” micro-cracks. The quantification of the Fourier domain filtered dataset and the analysis of the spatial proximity of the different types of damage provided the mechanism of cracking in metal matrix composites near regions of tri-axial stress at high compressive strains. The propensity for cracking in bulge region of SiCP/A6061 composite is attributed to the development and growth of acicularly shaped pores facilitated by repeated particle fragmentation. It results in a damage architecture that promotes the coalescence of the closely spaced pores and micro-cracks. This mechanism rationalises the high efficiency of power dissipation observed in hot working of SiCP/A6061composite in the absence of microstructural restoration processes.
2 citations
TL;DR: In this paper, a quantification protocol for a dataset obtained by scanning SiCP/A6061 composite strained upto ∼ 1 at 500°C is presented. But the performance of three different types of filters, namely Box, Gaussian and Butterworth, are compared.
1 citations
References
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TL;DR: In this article, a new method of modeling material behavior which accounts for the dynamic metallurgical processes occurring during hot deformation is presented, which considers the workpiece as a dissipator of power in the total processing system and evaluates the dissipated power co-contentJ = ∫o σ e ⋅dσ from the constitutive equation relating the strain rate (e) to the flow stress (σ).
Abstract: A new method of modeling material behavior which accounts for the dynamic metallurgical processes occurring during hot deformation is presented. The approach in this method is to consider the workpiece as a dissipator of power in the total processing system and to evaluate the dissipated power co-contentJ = ∫o σ e ⋅dσ from the constitutive equation relating the strain rate (e) to the flow stress (σ). The optimum processing conditions of temperature and strain rate are those corresponding to the maximum or peak inJ. It is shown thatJ is related to the strain-rate sensitivity (m) of the material and reaches a maximum value(J max) whenm = 1. The efficiency of the power dissipation(J/J max) through metallurgical processes is shown to be an index of the dynamic behavior of the material and is useful in obtaining a unique combination of temperature and strain rate for processing and also in delineating the regions of internal fracture. In this method of modeling, noa priori knowledge or evaluation of the atomistic mechanisms is required, and the method is effective even when more than one dissipation process occurs, which is particularly advantageous in the hot processing of commercial alloys having complex microstructures. This method has been applied to modeling of the behavior of Ti-6242 during hot forging. The behavior of α+ β andβ preform microstructures has been exam-ined, and the results show that the optimum condition for hot forging of these preforms is obtained at 927 °C (1200 K) and a strain rate of 1CT•3 s•1. Variations in the efficiency of dissipation with temperature and strain rate are correlated with the dynamic microstructural changes occurring in the material.
1,121 citations
TL;DR: In this article, a fracture initiation map is developed which should be useful in fast forming operations at strain rates greater than about 10-3 s-1 at elevated temperatures, and two types of cavitation mechanisms, one pertaining to cavity formation at second phase particles, as in ductile fracture, and the other pertaining to wedge type microcracking at grain boundaries, are considered.
Abstract: A fracture initiation map is developed which should be useful in fast forming operations at strain rates greater than about 10-3 s-1 at elevated temperatures. Two types of cavitation mechanisms, one pertaining to cavity formation at second phase particles, as in ductile fracture, and the other pertaining to wedge type microcracking at grain boundaries, are considered. In addition, dynamic recrystallization and adiabatic heating effects are considered. When these concepts are applied to aluminum, it is shown that there may be an intermediate region in the strain rate and temperature field in which neither of these mechanisms should operate and within which the material would, therefore, be safe from fracture.
313 citations
TL;DR: Mise en evidence, dans un alliage commercial d'aluminium renforce par des whiskers de SiC (SiC/2124 Al) soumis a des traitements thermomecaniques adequats, d'un comportement de type superplastique lors d'une deformation isotherme a des taux de deformation relativement elevees as mentioned in this paper.
205 citations
TL;DR: In this article, a silicon carbide whisker-reinforced aluminum alloy (20% SiC fibers in 2024 aluminum) is shown to exhibit tensile ductilities in the order of 300% when deformed under thermal cycling conditions (100 ⇇ 450° C ) and at low stresses ( σ ⋍ 20 MPa ).
114 citations
TL;DR: In this paper, the superplastic properties of a rapidly solidified, high strength P/M Al alloy and the same alloy reinforced with SiC particulates (SiCp) have been studied.
Abstract: The superplastic properties of a rapidly solidified, high strength P/M Al alloy and the same alloy reinforced with SiC particulates (SiCp) have been studied. To prepare superplastic test materials, a matrix alloy powder of composition 7.2Zn-2.4Mg-2Cu-0.2Zr-0.12Cr-0.2Co (Kaiser PM-64) and the powder mixed with 10 to 20 vol pct SiCp (~5 μm diameter) were thermomechanically processed to very fine equiaxed grain structures of ~6 μm and ~8 μm, respectively. Superplasticity in these materials was evaluated by characterizing (1) high temperature stability, (2) dynamic grain growth, (3) strain rate sensitivity, (4) flow stress behavior, (5) cavitation and cavitation control, and (6) total superplastic strain. It was observed that the PM-64 alloy could achieve a total elongation of over 800 pct, while the SiCp reinforced alloy could attain an elongation greater than 500 pct before failure. Also, it was shown that with the use of hydrostatic pressure during superplastic flow, cavitation could be controlled. Observations were made of the effect SiCp reinforcement particles had on the superplastic flow stress behavior. Interpretations are proposed to explain the role of particulates during superplastic straining.
89 citations