• Title, Summary, Keyword: Mobility of Dislocation

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Evaluation of Internal Stress and Dislocation Velocity in Creep with 25Cr-20Ni Stainless Steels (25Cr-20Ni계 스테인리스강의 크리프 변형중 내부응력과 운동전위밀도의 평가)

  • Park, In-Duck;Ahn, Seok-Hwan;Nam, Ki-Woo
    • Proceedings of the KSME Conference
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    • pp.296-301
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    • 2004
  • By the purpose to investigate the change of internal stress and mobile dislocation density in creep, the stress relaxation test is carried out in the condition of each strain. Mobile dislocation density increased until it reached minimum creep rate and after that, it decreased and internal stress didn't have the change approximately until it reached minimum creep rate and after that, it decreased. The stress relaxation rate is fast and approached zero after 1.5 seconds after the beginning of the stress relaxation. And the larger the applied stress is, the larger the internal stress is. By the evaluation of mobility of dislocation, the dislocations glide viscously in STS31OJlTB but it is the dislocations glide viscously which N passes by cutting Cr atom rather than typical viscosity movement after calculating mobility of dislocation.

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Investigation of anomalous hardening in NiAl Single crystals at intermediate temperatures (중간온도 영역에서의 NiAl 단결정 이상 경화거동에 대한 연구)

  • Yang Chulho
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.1390-1393
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    • 2005
  • The hardening model based on the dislocation mechanics is employed to study the experimentally observed high tensile elongations of NiAl along the [110] orientation at intermediate temperatures. In the hardening model proposed, a mobility of dislocation is assumed to be restricted to glide through the slip plane by forest dislocation and thermally activated cross-slip event. Overall deformation behavior of NiAl was greatly influenced by temperature-dependent dislocation mobility that both experimental and simulated yield stresses decreased as temperature increased. The results of simulation showed anomalous hardening behaviors analogous to those of experiment at certain circumstances. This behavior occurred due to the hardening contributions generated by cross-slip events that disable the dislocation motion in the primary slip systems. By comparing simulation results with experiments, it is confirmed that the proposed hardening model can represent anomalous tensile elongations due to the hardening by forest dislocations and cross-slip events.

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The Effect of Dislocation Pipe Diffusion on Electro-Migration-Induced Breakdown in an FCC Structure (면심입방구조에서 Electro-Migration-Induced Breakdown에 대한 전위파이프 확산의 영향)

  • 이득용
    • Journal of the Korean Ceramic Society
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    • v.28 no.11
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    • pp.878-884
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    • 1991
  • The mobility and diffusivity in an edge dislocation in an FCC crystal formed by the removal of one half of a (100) plane were evaluated in an applied field by analyzing a vacancy tight binding model using Stark's matrix technique. A model of an edge dislocation in an FCC crystal was constructed for a [100] Burgers vector where vacancy transport along the edge dislocation in an FCC crystal was constructed for a [100] Burgers vector where vacancy transport along the edge of the extrac half plane of ions was considered. The model considered a tight binding approximation of the vacancy to the compressed region of the core and carried the calculation to the limit of an infinite length of dislocation. The diffusivity and the ratio of mobility to diffusivity were found to increase without bounds in the limit where the correlation factor becomes zero. In contrast, as the correlation factor became unity, the diffusivity became zero and the ratio of mobility to diffusivity became unity associated with the uncorrelated limit of 1/kT. This implied that the phenomenon was not unique to the crystal structure but was unique to edge dislocations with vacancy tight binding.

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Evaluation of Internal Stress and Dislocation Velocity in Creep with Austenite Stainless Steels (오스테나이트계 스테인리스강의 크리프 변형중 내부응력과 운동전위밀도의 평가)

  • Kim Hyun Soo;Nam Ki Woo;Park In Duck
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.2
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    • pp.214-219
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    • 2005
  • To investigate the change of internal stress and mobile dislocation density in the creep, stress relaxation test was examined from each strain range. Mobile dislocation density increased until it reached minimum creep rate but after that, it decreased. Internal stress did not change until it reached minimum creep rate but after that, it decreased. The stress relaxation rate is fast and approached zero later 1.5 seconds, which were begun in the stress relaxation. When the applied stress is large, the internal stress is large. It is cleared that dislocations glide viscously which N passes by cutting Cr atom rather than typical viscosity movement by the evaluation of mobility of dislocation in STS310J1TB.

Study on the Dislocation Behavior during Creep in 12% Chromium Steel (12% Cr 강의 크리이프중 전위거동에 관한 연구)

  • Oh, Sea-Wook;Jang, Yun-Seok
    • Journal of Ocean Engineering and Technology
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    • v.4 no.2
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    • pp.112-120
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    • 1990
  • In order to check the effect of dislocation behavior on creep rate in 12% Chromium steel, 14 samples of different compositions were examined by creep rupture test, and subgrain sizes, distribution of dislocations and precipitates were checked. And, authors reviewed the behaviors of dislocations, the formation and growth of subgrains and precipitates during creep. The results are as the following: 1) Creep rates calculated by .epsilon. over dot = .rho.bv show 10-15% higher values than actual data measured. However, authors conclude that the density and velocity of dislocations together with subgrain size are important factors governing deformation during creep in 12% chromium steel. 2) The values of the strength of obstacles in the mobility of dislocations are more clearly depended on the effective stress in the range of $10{\pm}5kgf/mm^{2}$ and increase with the increase of temperature. 3) Creep rates decrease with the smaller sizes of subgrains formed and can result in the longer creep rupture lives(hours). The smaller subgrains can be made by forming shorter free gliding distances of dislocations with very fine precipitates formed in the matrix during creep by applying proper alloy design. 4) Dislocation mobility gets hindered by precipitates occurring, which are coarsened by the softening process governed by diffusion during long time creep.

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Multi-scale Modeling of Plasticity for Single Crystal Iron (단결정 철의 소성에 대한 멀티스케일 모델링)

  • Jeon, J.B.;Lee, B.J.;Chang, Y.W.
    • Transactions of Materials Processing
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    • v.21 no.6
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    • pp.366-371
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    • 2012
  • Atomistic simulations have become useful tools for exploring new insights in materials science, but the length and time scale that can be handled with atomistic simulations are seriously limiting their practical applications. In order to make meaningful quantitative predictions, atomistic simulations are necessarily combined with higher-scale modeling. The present research is thus concerned with the development of a multi-scale model and its application to the prediction of the mechanical properties of body-centered cubic(BCC) iron with an emphasis on the coupling of atomistic molecular dynamics with meso-scale discrete dislocation dynamics modeling. In order to achieve predictive multi-scale simulations, it is necessary to properly incorporate atomistic details into the meso-scale approach. This challenge is handled with the proposed hierarchical information passing strategy from atomistic to meso-scale by obtaining material properties and dislocation mobility. Finally, this fundamental and physics-based meso-scale approach is employed for quantitative predictions of the mechanical response of single crystal iron.

Dislocation Behavior around Crack Tips in Single Crystal Alumina (단결정 알루미나의 균열첨단에서 전위거동)

  • Kim, Hyeong-Sun;Robers, S.G
    • Korean Journal of Materials Research
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    • v.4 no.5
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    • pp.590-599
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    • 1994
  • A work on the brittle to ductile transition (BDT) in single crystal alumina has been performed to understand and assess the dynamics of dislocation mobility around crack tip of brittle material. The critical stress intensity factor and yield strengths were obtained from bending test using precracked specimens at elevated temperatures. It was found that the BDT temperature was dependent on strain rate and orientation of specimen : for (1120) fracture surface, $1034^{\circ}C$, $1150^{\circ}C$ for $4.2 \times 10^{-6}$, $4.2 \times 10^{-7}s^{-1}$ respectively. Under a 4 point bending test, the moving distance of dislocation generated near crack front in ductile range is determined by an etch pits method. The velocity of dislocation in sapphire obtained from the double etching method was applied to modelling study.

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Dislocations as native nanostructures - electronic properties

  • Reiche, Manfred;Kittler, Martin;Uebensee, Hartmut;Pippel, Eckhard;Hopfe, Sigrid
    • Advances in nano research
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    • v.2 no.1
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    • pp.1-14
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    • 2014
  • Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two-dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one-dimensional channels for holes.

Effects of Postannealing on GaN Grown by MOCVD on Reactive ion Beam Pretreated Sapphire Substrate (활성화 이온빔 처리된 사파이어 기판상 MOCVD로 성장시킨 GaN의 열처리 효과)

  • Lee, Sang-Jin;Byeon, Dong-Jin;Hong, Chang-Hui;Kim, Geung-Ho
    • Korean Journal of Materials Research
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    • v.11 no.3
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    • pp.191-196
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    • 2001
  • GaN is a key material for blue and ultraviolet optoelectronics. Postannealing process was employed to investigate the structural change and the effect on electrical property of the GaN thin film grown on reactive ion beam(RIB) treated sapphire (0001) substrate. Full width half maximum (FWHM) of double crystal x-ray diffraction (DCXRD) spectra and Hall mobility of the specimen were significantly changed depending on the postannealing time at $1000^{\circ}C$ in N2 atmosphere. FWHM of DCXRD reduced upto about 50arc-sec and the mobility increased about $80\textrm{cm}^2$/V.sec. The postannealed specimen with the best mobility was compared with sample without annealing by TEM. The former sample showed a decrease in the lattice strain and reduction of dislocation density by about 56~59%. This implies that there is a strong correlation between crystalline quality and the electrical property of the film. The Present results clearly show that the combination of RIB pretreatment and proper post annealing conditions results in the improved properties of GaN films grown by MOCVD.

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The Shoulder Pain due to Metastatic Breast Cancer -A Case Report-

  • Kim, Sae-Young;Jung, Min-Woo;Kim, Jin-Mo
    • The Korean Journal of Pain
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    • v.24 no.2
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    • pp.119-122
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    • 2011
  • A rotator cuff tear causes shoulder pain and limits movement of the shoulder joint. A chronic degenerative change or impingement is the reason for a rotator cuff tear. Diagnosis is made based on medical history and, physical and radiological examinations. Other causes of shoulder pain include calcific tendinitis, degenerative arthropathy, joint dislocation, fracture, and primary or metastatic neoplasm. However, metastatic cancer in the shoulder joint is difficult to diagnosis. We experienced a case in which a 46-year-old female patient complained of left shoulder pain and limited joint mobility, and these symptoms were due to metastatic breast cancer in the shoulder.