• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.3 s.22
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• pp.51-55
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• 2005

In this paper, a near net shape technology using superplasticity and diffusion bonding characteristics was presented for application to various components of aircraft and missiles. Due to these special characteristics of some aerospace alloys, it is possible to produce complex components to shape very near final dimension with enhanced design freedom, reduced material usage, and overall saving of weight and cost. The high pressure vessel for a space launcher was fabricated with Ti-6Al-4V alloy by superplastic forming and diffusion bonding process and the failure characteristics are compared with conventionally fabricated vessel spin formed and TIG welded. The structural integrity of the superplastic forming and diffusion bonding process was successfully demonstrated.

• Journal of the KSME
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• v.33 no.7
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• pp.628-635
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• 1993

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.132-139
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• 1995

Tnermomechanical treatment consisting of homogenizing, hot and warm rolling were introduced to Al-MgCu-Mn alloys for obtaining superplasticity. The factors affecting the superplasticity of the alloys were investigated by optical and transmission electron microscopy. Large particles which had not been decomposed during homogenizing treatments remained stable in the hot and warm rolling processes. These particles were a source of cavitation and poor elongation in superplastic deformation. On the other hand, fine precipitates were produced during thermomechanical processing, and resulted in improvement of superplasticity by stabilizing microstructure. Two-step homogenizing and air cooling process was more effective than onestep homogenizing and furance cooling process in removing microsegregations and producing fine particles.

• Defense and Technology
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• no.10 s.92
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• pp.11-17
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• 1986

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.76-79
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• 2009

The current understanding for phase/grain boundary sliding and low-temperature/high-strain rate superplasticity of two-phase titanium alloys is summarized. The quantitative analysis on boundary sliding revealed increased sliding resistance on the order of $\alpha/\beta\;\ll\;\alpha/\alpha\;\approx\;\beta/\beta$ boundary, hence, led to the conclusion that approximately 50% alpha(or beta) volume fraction and/or grain refinement is beneficial for obtaining large superplastic elongation at low temperature and/or high strain rate. To predict the temperature for 50% alpha volume in various alpha/beta Ti, artificial neural network was applied. Finally, much enhanced superplasticity was achieved through grain refinement utilizing dynamic globularization.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.5-10
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• 2010

The current understanding for phase/grain boundary sliding and low-temperature/high-strain rate superplasticity of two-phase titanium alloys is summarized. The quantitative analysis on boundary sliding revealed increased sliding resistance on the order of ${\alpha}/{\beta}\;\ll\;{\alpha}/{\alpha}\;{\approx}\;{\beta}/{\beta}$ boundary, hence, led to the conclusion that approximately 50% alpha(or beta) volume fraction and/or grain refinement is beneficial for obtaining large superplastic elongation at low temperature and/or high strain rate. To predict the temperature for 50% alpha volume in various alpha/beta Ti, artificial neural network was applied. Finally, much enhanced superplasticity was achieved through grain refinement utilizing dynamic globularization.

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.05a
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• pp.107-108
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• 1996

• Korean Journal of Materials Research
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• v.11 no.7
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• pp.585-589
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• 2001

Many experimental results have revealed that the development of cavitaition during tensile deformation is limited by the Presence of liquid phases. However, the presence of liquid phases does not always lead to high-strain-rate superplasticity, because too much liquid causes intergranular decohesion at grain boundaries/interfaces in metal-matrix composites. Thus, it is important to examine the nature of interfaces of superplastic composites in order to understand the origin of superplastic flow related to liquid grain boundaries during high-strain-rate superplastic deformation. This study shows that a large elongation is obtained at the temperature, that is close to the onset temperature for partial melting in the superplastic composites, but the elongation significantly decreases at slightly higher temperatures, which are close to the end temperature fur partial melting. This indicates that there is an optimum amount of the liquid phase for obtaining high-strain-rate superplasticity in these materials.

• Korean Journal of Materials Research
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• v.27 no.1
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• pp.53-61
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• 2017

Magnesium alloys are of emerging interest in the automotive, aerospace and electronic industries due to their light weight, high specific strength, damping capacity, etc. However, practical applications are limited because magnesium alloys have poor formability at room temperature due to the lack of slip systems and the formation of basal texture, both of which characteristics are attributed to the hcp crystal structure. Fortunately, many magnesium alloys, even commercialized AZ or ZK series alloys, exhibit superplastic behavior and show very large tensile ductility, which means that these materials have potential application to superplastic forming (SPF) of magnesium alloy sheets. The SPF technique offers many advantages such as near net shaping, design flexibility, simple process and low die cost. Superplasticity occurs in materials having very small grain sizes of less than $10{\mu}m$ and these small grains in magnesium alloys can be achieved by thermomechanical treatment in conventional rolling or extrusion processes. Moreover, some coarse-grained magnesium alloys are reported to have superplasticity when grain refinement occurs through recrystallization during deformation in the initial stage. This report reviews the characteristics of superplastic magnesium alloys with high-strain rate and coarse grains. Finally, some examples of SPF application are suggested.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.187-188
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• 2008