• Title/Summary/Keyword: Superplasticity

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Nanostructured Bulk Ceramics (Part II. Superplasticity and High Strain Rate Superplasticity)

  • Han, Young-Hwan;Mukherjee, Amiya K.
    • Journal of the Korean Ceramic Society
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    • v.46 no.4
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    • pp.345-349
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    • 2009
  • In Part II, the paper will describe a three-phase alumina-based nanoceramic composite demonstrating superplasticity at a surprisingly lower temperature and higher strain rate. One important factor in the processing of these nanocomposites was the use of the electrical field assisted sintering method, SPS. These improvements in mechanical properties were briefly discussed in the context of the results from the microstructural investigations. SPS forming approach provides a new route for low temperature and high-strain-rate superplasticity for nanostructured materials and should impact and interest a broad range of scientists in materials research and superplastic forming technology.

Low-temperature/high-strain rate superplasticity of two-phase titanium alloys (2상 타이타늄 합금의 저온/고속 초소성)

  • Part, C.H.;Lee, C.S.
    • 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.

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Enhanced Superplasticity of Two-phase Titanium Alloys by Microstructure Control (2상 타이타늄 합금의 미세조직 제어를 통한 초소성 특성 향상)

  • Park, C.H.;Lee, C.S.
    • 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.

Superplasticity of Magnesium Alloys and SPF Applications (마그네슘합금의 초소성 특성과 응용)

  • Shim, Jae-Dong;Byun, Ji-Young
    • 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.

Effect of Processing Variables on the High Temperature Formability of AZ31 Mg alloy (AZ31 Mg 합금의 가공 조건에 따른 고온 성형성 연구)

  • Lee B. H.;Shin K.S.;Lee C.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.05a
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    • pp.80-83
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    • 2004
  • High temperature deformation behavior of AZ31 Mg alloy was investigated in this study on the basis of a processing map $(\varepsilon\approx0.6)$. To construct a processing map, compression tests were carried out at wide range of temperatures and strain rates $(T=250\~500^{\circ}C,\;\varepsilon=10^{-4}\~100/s)$. Two regions of high deformation efficiency $(\eta)$ were identified as: (1) a dynamic recrystalization (DRX) domain at $250^{\circ}C$ and 1/s and (2) a superplasticity domain at $450^{\circ}C$ and $10^{-4}/s$. Possible deformation mechanisms operating at high temperature were discussed in relation to the activation energy. A two-stage deformation method was found to be effective in enhancing the superplasticity of AZ31 Mg alloy. From the two-stage deformation method, tensile elongation of $1200\%$ was obtained at the superplastic domain.

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Development of Aerospace Components Forming Technology using Superplasticity and Diffusion Bonding Characteristic (초소성 및 확산접합을 이용한 우주항공 부품 성형기술 개발)

  • Lee, Ho-Sung;Yoon, Jong-Hoon;Yi, Yeong-Moo
    • 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.

Low-Temperature Superplastic Deformation Behavior of Fine-Grained Ti-6Al-2Sn-4Zr-2Mo-0.1Si Alloy (미세 결정립 Ti-6Al-2Sn-4Zr-2Mo-0.1Si 합금의 저온 초소성 변형 거동)

  • Park, C.H.;Lee, B.;Lee, C.S.
    • Transactions of Materials Processing
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    • v.18 no.7
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    • pp.544-549
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    • 2009
  • This study aimed to elucidate the deformation mechanism during low-temperature superplasticity of fine-grained Ti-6Al-2Sn-4Zr-2Mo-0.1Si alloy in the context of constitutive equation. For this purpose, initial coarse equiaxed microstructure was refined to $2.2{\mu}m$ via dynamic globularization. Globularized microstructure exhibited large superplastic elongations(434-826%) at temperatures of $650-750^{\circ}C$ and strain rate of $10^{-4}s^{-1}$. It was found that the main deformation mechanism of fine-grained material was grain boundary sliding accommodated by dislocation motion with both stress exponent (n) and grain size exponent (p) values of 2. When the alpha grain size, not sub-grain size, was considered to be an effective grain size, the apparent activation energy for low-temperature superplasticity of the present alloy(169kJ/mol) was closed to that of Ti-6Al-4V alloy(160kJ/mol).

Superplastic Deformation Behavior of ECA dressed 7010 Al Alloy (ECAP가공된 7010 Al 합금의 초소성 변형 특성)

  • 김지식
    • Transactions of Materials Processing
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    • v.11 no.3
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    • pp.255-261
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    • 2002
  • The grain size of 7010 Al alloy was refined to submicrometer level by using equal channel angular pressing (ECAP) and additional warm rolling. The mechanisms of grain refinement in ECAP process were fragmentation of coarse grain to ultra fine subgrains after a few passes and continuous recrystallization of the subgrains with the increase o( passes. Because of ultrafine grain size, essentially low temperature and high strain rate superplasticity was observed after ECAP process and warm rolling to form a sheet metal. The maximum elongation of 700% was obtained for an ECA pressed specimen after IS passes without warm rolling at $450^{\circ}C$ with strain rate of 5x$10^{-3}$/sec.