• 제목/요약/키워드: Superplasticity

검색결과 57건 처리시간 0.026초

Application of Pseud-superplastic PM Process to Ti-Al Intermetallic Compound for MEMS Parts

  • Miyano, Naoki;Kumagai, Yusuke;Yoshimoto, Masayoshi;Nishimura, Yuta;Tanaka, Shigeo;Ameyama, Kei
    • 한국분말야금학회:학술대회논문집
    • /
    • 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
    • /
    • pp.1292-1293
    • /
    • 2006
  • A non-equilibrium powder metallurgy processing such as an MA/SPS (Mechanical Alloying / Spark Plasma Sintering) process is examined in a Ti-48moll%Al. TiAl intermetallic compound is a potential light-weight/high-temperature structural material. One of the major problems, however, limiting the practical use of the material is its poor workability. From this point, the powder metallurgy (PM) processing route has been attractive alternative of the conventional processing for such material The MA/SPS process is able to apply to a LIGA process. Optimization of the pseudo-superplasticity enables to fabricate micro-parts made of fine grained ceramics composites of TiAl by the LIGA process.

  • PDF

Y-TZP의 燒結性 및 相 安定性에 대한 CuO添加의 影響 (Influence of CuO Dopants on the Sintering Ability and Phase Stability of Yttria-Stabilized Tetragonal Zirconia Polycrystals)

  • 피재환;김윤해
    • 한국해양공학회지
    • /
    • 제13권2호통권32호
    • /
    • pp.35-40
    • /
    • 1999
  • Effects of CuO addition on the sintering ability and the phase stability of Y-TZP. (Yttria doped Tetragonal Zirconia Polycrystals) were studied. The CuO dopants were found to be quite effective in reducing the sintering temperature to obtain full density and refining the grain size. The maximum allowable concentration of the dopants was limited to 0.3%mol% for CuO to maintain fully tetragonal phase. With the addition of these dopants, the flexual strength decreased by 20% in comparison with the undoped specimen but the fracture toughness increased by 15%.

  • PDF

AZ31 합금의 온간 부풀림 성형시 결정립 변화에 관한 연구 (Grain Evolution during Bulge Blow forming of AZ31 Alloy)

  • 백성규;이영선;이정환;권용남
    • 한국소성가공학회:학술대회논문집
    • /
    • 한국소성가공학회 2008년도 추계학술대회 논문집
    • /
    • pp.452-455
    • /
    • 2008
  • In the present study, blow forming characteristics of commercially roiled AZ31 alloy sheets were investigated. Two different kinds of AZ31 sheets were originally fabricated by using direct casting and strip casting methods respectively. Both sheets have similar grain sizes of about $7{\mu}m$ with a relatively equiaxed structure after rolling. A series of tensile tests were carried out to get flow behavior in terms of temperature and strain rate. Also, grain size effect was investigated by annealing as-received sheet at elevated temperatures. Elongation increased with temperature increment as well expected. However, the differences in tensile test condition did not give much difference in elongation even at the temperature range where a large elongation would be expected with such as fine grain of $7{\mu}m$. Blow forming experiments showed that forming condition did not result in higher difference in dome height. However, the interesting feature from this study was that formability of this AZ31 alloy got different with stress condition. Firstly, biaxial stress condition might result in lower temperature and strain rate dependencies compared to uniaxial tension results for both DC and SC sheets. Secondly, DC showed slower grain growth in uniaxial tension than in biaxial stress state while SC has much higher grain growth rage in uniaxial tension than in bulging.

  • PDF

구형 압력용기의 초소성 성형 공정에서 두께변화 예측에 관한 이론해석

  • 윤종훈;이호성;장영순;이영무
    • 항공우주기술
    • /
    • 제2권2호
    • /
    • pp.133-141
    • /
    • 2003
  • 초소성 공정을 이용하여 구형 압력용기를 제작하는 경우 두께와 구형의 형상은 일정하지 않고 성형공정이 진행함에 따라 변하게 된다. 본 연구에서는 공정과정 동안 발생하는 초기 블랭크의 두께변화 예측을 이론적으로 해석하였다. 두께변화 예측을 위한 이론적인 모델은 Kuglov 등이 적용한 박막이론을 사용하였으며 요구되는 최종 두께를 얻기 위한 초기 블랭크의 두께, 블랭크의 균일한 변형을 얻기 위한 시간에 따른 압력 프로파일, 각 성형단계에서 위치에 따른 두께분포 및 시간에 따른 두께분포를 결정하였다. 공정 단계 전반에 걸쳐서 적용 모델 및 해석 프로그램의 적합성을 문헌의 시험 결과와 비교하여 검증하였다.

  • PDF

Al-Cu-Zr 합금 초소성 성형품의 기계적 성질 (mechanical properties of Al-Cu-Zr alloy parts by superplastic forming)

  • 이영선
    • 한국소성가공학회:학술대회논문집
    • /
    • 한국소성가공학회 1999년도 춘계학술대회논문집
    • /
    • pp.163-170
    • /
    • 1999
  • Although the bulge forming technique is currently employed in commercial superplastic forming processes, the uniaxial tensile test is still the most commonly used method for the evaluation of the superplasticity of materials due to its simplicity in testing. However, the results obtained from the uniaxial tensile test can not be applied in analyzing the characteristics of the real parts formed in multi-axial stress state. In this paper, using the tensile test specimen obtained from the square cup manufactured by superplastic forming, tensile strength and elongation have been investigated according to the strain and cavity volume fraction. From the result of experiment, tensile strength and elongation are decreased according to the strain and cavity in Al-6%Cu-0.4%Zr alloy. On condition of uniaxial stress, cavity volume fraction is increased on linear according to the increasement of thickness strain. However, on condition of biaxial stress there are critical point( E t=1.5-1.6) that the slope, the ratio of cavity volume fraction and strain, have been changed. Therefore, cavity volume fraction is different with respect to stress condition, although the same strain.

  • PDF

저온 분사 코팅 공정에서 충돌속도에 따른 CuNiTiZr 벌크 비정질 소재의 활성화 에너지와 결정화 거동 분석 (Effects of Impact Velocity on Crystallization and Activation Energy of Cu-based Bulk Metallic Glasses in Kinetic Spray Coating)

  • 윤상훈;배규열;김정환;이창희
    • 한국표면공학회지
    • /
    • 제41권6호
    • /
    • pp.301-307
    • /
    • 2008
  • In this paper, nanocrystallization of CuNiTiZr bulk metallic glass (BMG) subjecting to a kinetic spraying, dependent on impact velocity, was investigated by numerical and experimental approaches. The crystallization fraction and nucleation activation energy of initial feedstock and as-deposited coating were estimated by DSC and Kissinger method, respectively. The results of numerical modeling and experiment showed that the crystalline fraction and nucleation activation energy in BMG coatings were depended on kinetic energy of incident particle. Upon impact, the conversion of particle kinetic energy leads to not only decreasing free energy barrier but also increasing the driving force for an amorphous to crystalline phase transformation. The nanocrystallization of BMGs is associated with the strain energy delivered by a plastic deformation with a high strain rate.

Al-Mg합금의 압연변수에 다른 미세구조의 변화와 고온인장특성 (The effects of rolling process on microstructures and high temperature tensile properties of Al-Mg alloy)

  • 김태규;전채홍;권숙인;박종우
    • 열처리공학회지
    • /
    • 제10권2호
    • /
    • pp.81-92
    • /
    • 1997
  • The effect of alloying elements, precipitate size, its distribution, and dislocation substructure resulted from warm rolling or cold rolling in the superplastic Al-Mg alloy system was investigated. One of the major requirements for fine structure superplasticity is that the grain size should be very small. Fine grain structure is controlled by the dislocation substructure and the dynamic recrystallization during hot or warm working. The recovery of Al-Mg base alloys was constrained resulting in relatively high dislocation density when the alloys were warm rolled. In particular, Al-Mg-Zr alloy exhibited the smallest sub-grain size among Al-Mg alloys containing Mn, Cu, Zr as a third element. The Al-Mg-Mn alloy cold rolled 80% after hot rolling showed the maximun strain rate sensitivity exponent, m, of 0.75 under strain rate of $7.1{\times}10^{-4}/s$ at $500^{\circ}C$. The elongation of the alloys was limited in spite of high m values due to large dispersoids containing appreciable amount of Fe impurities.

  • PDF

ECAP가공에 의한 초미세립 소재의 기계적 물성 (Mechanical Properties of Ultrafine Grained Materials via Equal-Channel Angular Pressing)

  • 고영건;김우겸;안정용;박경태;이종수;신동혁
    • 소성∙가공
    • /
    • 제15권2호
    • /
    • pp.105-111
    • /
    • 2006
  • A study was made to investigate the microstructure and the mechanical properties of low-carbon steel, Al-Mg alloy and Ti-6Al-4V alloy each representing bcc, fcc and hcp crystal structures, respectively fabricated by equal-channel angular(ECA) pressing. After a series of ECA pressings was performed, most grains were significantly refined below ${\mu}m$ in diameter with high mis-orientation of grain boundaries irrespective of different crystal structure used. Regarding the strain hardening capability, tensile tests of ultrafine grain (UFG) dual-phase (ferrite/martensite) steel which was different from UFG ferrite-pearlite steel were carried out at ambient temperature, and corresponding mechanical properties were discussed in relation to modified C-J analysis. Low-temperature and/or high strain-rate superplasticity of the UFG Al-Mg alloy and UFG Ti-6Al-4V alloy were also studied. Based on the analysis used in this study, it was concluded that UFG alloys exhibited the enhanced mechanical properties as compared to coarse-grained (CG) counterparts.

고온에서 $Zr_{55}Al_{10}Ni_5Cu_{30}$ 벌크 유리금속의 변형거동 (Deformation Behavior of a $Zr_{55}Al_{10}Ni_5Cu_{30}$ Bulk Metallic Glass at High Temperatures)

  • 정영진;김기현;오상엽;신형섭
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2004년도 춘계학술대회
    • /
    • pp.342-347
    • /
    • 2004
  • The deformation behavior of a $Zr_{55}Al_{10}Ni_5Cu_{30}$ bulk metallic glass under tensile loading at different range of strain rates and temperatures between 680 K and 740 K were investigated. The variation in the deformation behavior of $Zr_{55}Al_{10}Ni_5Cu_{30}$ bulk metallic glass which resulted from the crystallization induced during testing was reported. The$Zr_{55}Al_{10}Ni_5Cu_{30}$ bulk metallic glass has showed either homogeneous or inhomogeneous deformation depending on test condition. It exhibited a maximum elongation of about 560 % at the condition of $407^{\circ}C{\times}\;10^{-4}/s$. The flow behavior exhibited three different types and the flow stress became lower at higher temperatures and lower strain rates. The increase of the time elapsed during heating resulted in the partial crystallization of bulk metallic glass phase and eventually strain hardening and brittle fracture.

  • PDF

과냉각 구간에서 Cu-계 아몰퍼스 복합재의 변형거동 (Deformation behavior of Copper Amorphous Composites in Super Cooled Liquid Region)

  • 박은수;김지수;김휘준;배정찬;허무영
    • 한국소성가공학회:학술대회논문집
    • /
    • 한국소성가공학회 2005년도 춘계학술대회 논문집
    • /
    • pp.279-282
    • /
    • 2005
  • Composites comprising various volume fractions of crystalline nickel and bulk amorphous (BA) were produced by means of electroless coating of nickel on BA powder of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ and subsequent spark plasma sintering (SPS) of coated BA powder. The flow curves of composites at various temperatures in the supercooled liquid region were determined by the uniaxial compression test with various strain rates. During compression at $450^{\circ}C$ with $\dot{\varepsilon}=2\times10^{-3}$, the monolithic BA sample and crystalline-BA composites displayed the superplastic deformation with $\varepsilon>1.4$. At temperatures above $460^{\circ}C$, the stress-strain curve of the monolithic BA sample depicted a sharp peak stress and a fellowing stress drop due to cracking, while those of the crystalline-BA composites displayed work-hardening up to the imposed strain. FEM analysis indicated that a fairly homogeneous strain state prevailed throughout the composite, while a higher level of stress was obtained in a harder BA.

  • PDF