• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.291-293
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• 1997

The effect of strain accumulation on the superplastic deformation behavior has been investigated through a series of load relaxation tests. The experimental results were analyzed using the recently proposed inelastic constitutive theory. The superplastic deformation of fine grained materials is confirmed to consist of grain boundary sliding and accommodating grain matrix deformation. However the flow behavior is changed with the plastic strain. It is believed that the microstructural changes such as grain growth and cavitation affect the superplastic deformation behaviors.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.65-71
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• 1998

The superplastic deformation behaviors of 7075Al alloy have been characterized experimentally and analyzed by the internal variable theory of inelastic deformation. A simple rheological model including the grain boundary sliding has been used to interpret the superplastic deformation behaviors. A series of load relaxation and tensile tests have been carried out for 7075Al alloy at the various temperatures. The superplastic deformation of 7075Al alloy is confirmed to consist of the grain boundary sliding and accommodating grain matrix defprmation.

• Transactions of Materials Processing
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• v.18 no.6
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• pp.448-452
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• 2009

Superplastic deformation behavior and texture evolution after equal channel angular pressing (ECAP) of Zn-0.3Wt%Al alloy were investigated in this study. ECAP was conducted at temperatures from $60^{\circ}C$ to $160^{\circ}C$ on the plate type specimens of 5 mm thickness and 20 mm width. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED, which is called shear texture. Tensile tests were carried out at $100^{\circ}C$ for ECAPed specimens under the strain rate of 0.0002/s. After ECAP of the Zn-0.3Wt%Al alloy, elongation was dramatically increased up to 500% at $100^{\circ}C$. The effect of ECAP on the anisotropy in the superplastic deformation behavior was negligible.

• Journal of the Korean Ceramic Society
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• v.33 no.6
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• pp.718-724
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• 1996

Deformation mechanism map of Langdon-Mohammed type for YBa2Cu3O7-x superconducting ceramic was constructed by considering mechanisms of Nabarro-Herring Coble and powder-law creep and grain boundary sliding (GBS) with an accommodation by grain boundary diffusion. The map was found consistent with experi-mental results not only of the creep the also of the superplastic deformation. It showed the transition from interface reaction-controlled to the grain boundary diffusion-controlled GBS mechanism at about 1 ${\mu}{\textrm}{m}$ grain size and 100 MPa flow stress in agreement with the experimental results.

• Transactions of Materials Processing
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• v.21 no.3
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• pp.151-159
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• 2012

Finite element simulations were conducted to investigate the influence of grain growth in the superplastic blow forming process. A microstructure-based constitutive model considering grain growth effects is proposed and used in the simulations. Also, a grain growth rate equation accounting for both static and dynamic grain growth is implemented. The simulations were made using a 2D plane-strain model for constrained blow forming and an axisymmetric model for free bulging. These two models showed different features during the forming stages. However, the forming pressure-time curve and the thickness distribution obtained by both simulations explained well the deformation hardening induced by the grain growth during superplastic forming. This study shows that grain growth is an important factor in determining the material behavior during superplastic deformation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.228-231
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• 1997

A series of load relaxation tests was performed to determine stress-strain rate curves at high temperatures. Constitutive parameters of GBS and GMD were evaluated from the curves using the recently proposed inelastic deformation theory. Tensile tests and Microsturcture investigations showed deformation behavior as the relaxation test results predicted.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.421-424
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• 2009

Superplastic deformation behavior and texture evolution after equal channel angular pressing (ECAP) of Zn-0.3Al alloy were investigated in this study. ECAP was conducted at temperatures from $40^{\circ}C$ to $160^{\circ}C$ on the plate type specimens of 5 mm thickness and 20 mm width. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED. A series of compression and tensile tests was carried out at temperatures from RT to $200^{\circ}C$ under the strain rate from 0.03 to 10/s. After ECAP of the Zn-Al alloy, elongation was dramatically increased up to 1000% at above $60^{\circ}C$. The effects of ECAP on the texture and anisotropy in the superplastic deformation bebavior were found to be negligible.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.129-130
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• 1999

The superplastic deformation characteristics is powder metallurgy(PM) Al-Li alloy has been studied within the framework of a recently proposed internal variable theory of superplasticity(SSP). The flow curves were obtained by performing a series of load relaxation tests at the temperature range from 45$0^{\circ}C$ to 52$0^{\circ}C$ It has been found that the overall flow curves were separated into the grain boundary sliding(GBS) and the accommodating dislocation glide processes/ The tensile curves were also obtained to clarify the superplastic deformation bahavior of PM Al-Li alloy. The microstructural features of PM AL-Li alloy have been examined through the transmission electron microscopy.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.193-200
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• 2007

Micro forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Al5083 superplastic alloy with very small grains has a great advantage in achieving micro deformation under low stress due to its relatively low strength at a specific high temperature range. Micro forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk Metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, the micro formability of Al5083 superplastic alloy and bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$, was investigated with the specially designed micro vibration forming system using pyramid-shape, V-shape and U-shape micro die pattern. With these dies, micro vibration forming was conducted by varying the applied load, time. Micro formability was estimated by comparing the hight of formed shape using non-contact surface profiler system. The vibration load effect to metal flow in the micro die and improve the micro formability of Al5083 superplastic alloy and $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk Metallic glass(BMG).

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.876-886
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• 1994

Process design in superplastic forming to produce a Nickel-base jet engine disk has been carried out using the rigid-viscoplastic finite element method. This study aims at deriving systematic procedures in forging of superalloy engine disk, and develops a simple scheme to control strainrate within a range of superplastic deformation during the forging operation. The new process, a pancake type preform being used, is designed to have less manufacturing time, and more even distribution of effective strain in the final product, while the conventional superplastic forging of an engine disk has been produced from a cylindrical billet. The jet engine company, Pratt & Whitney, provided the basic information on the manufacturing process of superplastic forging of a jet engine disk.