• Title, Summary, Keyword: microstructure

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Process Design and Microstructure Evaluation During Hot Forging of Superalloy Turbine Disk (초내열합금 터빈 디스크의 열간 단조 공정에 대한 공정 설계 및 미세조직 평가)

  • Cha, D.J.;Kim, D.K.;Kim, Y.D.;Bae, W.B.;Cho, J.R.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.190-194
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    • 2007
  • The forging process design and microstructure evolution for gas turbine disk of a Waspaloy is investigated in this study. Parameters related to deformation are die and preform geometry, and forging temperature of die and workpiece. Die and preform design are considered to reduce the forging load, and to avoid the forging defects. Blocker and finisher dies for multistage forging are designed and the initial billet geometry is determined. The control of hot forging parameters such as strain, strain rate and temperature also is important because the microstructure change in hot working affects the mechanical properties. The dynamic recrystallization evolution has been studied in the temperature range 900-$1200^{\circ}C$ and strain rate range 0.01-1.0s-1 using hot compression tests. Modeling equations are required represent the flow curve, recrystallized grain size, recrystallized volume fraction by various tests. In this study, we used to thermo-viscoplastic finite element modeling equation of DEFORM-2D to predict the microstructure change evolution during thermo-mechanical processing. The microstructure is updated during the entire thermal and deformation processes in forging.

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EBSD Microstructural Characterisation of Oxide Scale on Low Carbon Steel

  • Birosca, S.;De Cooman, B.C.
    • Corrosion Science and Technology
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    • v.7 no.3
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    • pp.182-186
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    • 2008
  • The microstructures of the oxide scale developed at high temperature on steels are very complex and their development depends on many factors including time, temperature, oxidation conditions and alloying elements. The classical model of an oxide scale on steel consisting of wüstite, magnetite and haematite layers, is more complicated in reality and its properties change with the factors that affect their development. An understanding of the oxide scale formation and its properties can only be achieved by careful examination of the scale microstructure. The oxide scale microstructure may be difficult to characterise by conventional techniques such as optical or standard scanning electron microscopy. An unambiguous characterisation of the scale and the correct identification of the phases within the scale are difficult unless the crystallographic structure for each phase in the scale is considered and a simultaneous microstructure-microtexture analysis is carried out. In the current study Electron Backscatter Diffraction (EBSD) has been used to investigate the microstructure of iron oxide layers grown on low carbon steels at different times and temperatures. EBSD has proved to be a powerful technique for identifying the individual phases in the oxide scale accurately. The results show that different grain shapes and sizes develop for each phase in the scale depending on time and temperature.

Evaluation of Homogeneous Ultra-fine Grain Refinements via Equal Channel Angler Pressing Process (등통로각압축공정을 통한 결정립의 균질한 초미세립화에 대한 고찰)

  • Kim, W.;Lee, H.H.;Seo, S.J.;Lee, J.K.;Yoon, T.S.;Kim, H.S.
    • Transactions of Materials Processing
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    • v.27 no.4
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    • pp.222-226
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    • 2018
  • Severe plastic deformation (SPD) is a promising method for drastically enhancing the mechanical properties of the materials by grain refinement of metallic materials. However, inhomogeneous deformation during the SPD process results in the inhomogeneous microstructure of the SPD-processed material. We manufactured cylindrical copper specimens of 42 mm in diameter with ultrafine grains (UFG) using an equal channel angular pressing (ECAP) to figure out the relationship between homogeneous microstructure and the number of the processing passes. Two specimens, which are ECAP-processed 4 times (4pass) and 6 times (6pass) each with Route Bc, are prepared for comparison of mechanical properties and microstructure. The results show that the mechanical properties of the two specimens (4pass and 6pass) are similar. Moreover, both the specimens show highly enhanced mechanical properties. The 4pass specimen, however, shows inhomogeneity in hardness distribution, while the 6pass specimen shows a homogeneous distribution. Microstructure analysis reveals that the 4pass specimen has an inhomogeneous microstructure with incompletely refined grain structure. This inhomogeneity of the 4pass specimen could be explained by the circumferential rotation during ECAP process.

Microstructure and Properties of $Cr_{2}O_{3}$additive ternary PZT Ceramics ($Cr_{2}O_{3}$이 첨가된 PNN-PZT 압전세라믹스에서의 미세구조 및 특성)

  • 박정호;김철수;김성곤;이상렬
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.972-975
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    • 2001
  • The effect of Cr$_2$O$_3$(0 to 0.5 wt%) doping on the microstructure and electrical properties of ternary Pb(Zr,Ti)O$_3$-Pb(Ni,Nb)O$_3$piezoelectric ceramic has been investigated. Abnormal grain growth (grain size 3.3 to 11.2 $\mu$m) and densification are found. Minor additives of $\leq$0.1 wt% improve the mechanical coupling factor, but with more additives of $\geq$0.2 wt% electrical properties deteriorate. Thus, these phenomna can be ascribed mainly to anomalous developed microstructure. The large grains were composed of a core region that is free of Cr and a surrounding shell region rich in Cr. The interfaces between the core and the shell were composed of misfit dislocations. The mechanical properties of the specimens were strongly influenced by this microstructural change. The microstrutural and compositonal evolution of the specimens containing different amounts of Cr$_2$O$_3$were monitored. Electrical properties were measured and related to the variations in the microstructure.

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Study for Heat Treatment Optimization of Titanium Hollow Casted Billet (타이타늄 중공마더빌렛 주조재의 열처리공정 최적화 연구)

  • Youn, Chang-Suk;Park, Yang-Kyun;Lee, Hyung-Wook;Lee, Dong-Geun
    • Journal of the Korean Society for Heat Treatment
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    • v.32 no.2
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    • pp.68-73
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    • 2019
  • ${\alpha}$-titanium alloy has a relatively low heat treatment characteristic and it is mainly subjected to heat treatment for residual stress, recovery or dynamic recrystallization. In this study, commercially pure titanium hollow castings was fabricated by gravity casting. Heat treatments were carried out at $750^{\circ}C$, $850^{\circ}C$ and $950^{\circ}C$ to investigate the effect of post-heat treatment on microstructure and mechanical properties. Beta-transus temperature ($T_{\beta}$) was about $913^{\circ}C$, and equiaxed microstructure was shown at temperature below $T_{\beta}$ and lath-type microstructure at temperature above $T_{\beta}$. Microstructure and mechanical properties did not show any significant difference in the direction of solidification for titanium hollow billet, so it can be seen that it was a well-made material for extrusion process. The optimum heat treatment condition of hollow billet castings for the seamless tube production was $850^{\circ}C$, 4 hr, FC, indicating a combination of equiaxed microstructure and appropriate mechanical properties.

Fabrication of Multi-stepped Three Dimensional Silicon Microstructure for INS Grade Servo Accelerometer (관성 항법 장치급 서보 가속도계용 다단차 3차원 실리콘 미세 구조물 제작)

  • Yee, Young-Joo;Lee, Sang-Hoon;Chun, Kuk-Jin;Kim, Yong-Kwon;Cho, Dong-Il
    • Proceedings of the KIEE Conference
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    • pp.425-427
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    • 1996
  • New fabrication technique was developed to make three dimensional silicon microstructure with five fold vertical steps through entire wafer thickness. Each step is pre-defined on multiply stacked thermal oxide and silicon nitride (O/N) layers by photolithographies. Multi-stepped silicon microstructure is formed by anisotropic etch in aqueous KOH solution with the patterned nitride film as masking layer. Fabricated microstructure consists of four $16{\mu}m$ thick flexural spring beams, $290{\mu}m$ thick proof mass, mesas for overrange stop with $10{\mu}m$ height from the surface of the proof mass, and the other mesas and V grooves used for assembling this structure to the packaging frame of pendulous servo accelerometer. Using the numerical finite element method (FEM) simulator: ABAQUS, mechanical characteristics of the fabricated microstructure by the developed technique was compared with those of the same structure processed by one step silicon bulk etch followed by oxidation and patterning the etched region.

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Effect of Annealing Conditions on Microstructure and Damping Capacity in AZ61 Magnesium Alloy (열처리조건에 따른 AZ61 마그네슘 합금의 미세조직과 감쇠능에 미치는 영향)

  • Ahn, Jae-Hyeon;Kim, Kwon-Hoo
    • Journal of the Korean Society for Heat Treatment
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    • v.31 no.2
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    • pp.56-62
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    • 2018
  • Many researchers have studied on the precipitation control after solution treatment to improve the damping capacity without decreasing the strength. However, studies on the damping capacity and microstructure changes after deformation in the solid solution strengthening alloys were inadequate, such as the Al-Zn series magnesium alloys. Therefore, in order to investigate the effect of annealing condition on microstructure change and damping a capacity of AZ61 magnesium alloy. In this study, it was confirmed that the microstructure changes affect the damping capacity and hardness when annealed AZ61 alloy. AZ61 magnesium alloy was rolled at $400^{\circ}C$ with rolling reduction of 30%. These specimens were annealed at $350^{\circ}C$ to $450^{\circ}C$ for 30-180 minutes. After annealing, microstructure was observed by using optical microscopy, and damping capacity was measured by using internal friction measurement machine. Hardness was measured by Vickers hardness tester under a condition of 0.3 N. In this study, static recrystallization was observed regardless of the annealing conditions. In addition, uniform equiaxed grain structure was developed by annealing treatment. Hardness is decreased with increasing grain size. This is associated with Hall-Petch equation and static recrystallization. In case of damping capacity, bigger grain size show the larger damping capacity.

Change in Microstructure and Mechanical Properties through Thickness with Annealing of a Cu-3.0Ni-0.7Si Alloy Deformed by Cold Rolling (냉간압연된 Cu-3.0Ni-0.7Si 합금의 어닐링에 따른 두께방향으로의 미세조직 및 기계적 특성 변화)

  • Lee, Seong-Hee;Han, Seung Zeon
    • Korean Journal of Materials Research
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    • v.28 no.2
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    • pp.113-117
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    • 2018
  • Effects of annealing temperature on the microstructure and mechanical properties through thickness of a cold-rolled Cu-3.0Ni-0.7Si alloy were investigated in detail. The copper alloy with thickness of 3 mm was rolled to 50 % reduction at ambient temperature without lubricant and subsequently annealed for 0.5h at $200{\sim}900^{\circ}C$. The microstructure of the copper alloy after annealing was different in thickness direction depending on an amount of the shear and compressive strain introduced by rolling; the recrystallization occurred first in surface regions shear-deformed largely. The hardness distribution of the specimens annealed at $500{\sim}700^{\circ}C$ was not uniform in thickness direction due to partial recrystallization. This ununiformity of hardness corresponded well with an amount of shear strain in thickness direction. The average hardness and ultimate tensile strength showed the maximum values of 250Hv and 450MPa in specimen annealed at $400^{\circ}C$, respectively. It is considered that the complex mode of strain introduced by rolling effected directly on the microstructure and the mechanical properties of the annealed specimens.

Microstructure Characterization of the Solders Deposited by Thermal Evaporation for Flip Chip Bonding (진공 증발법에 의해 제조된 플립 칩 본딩용 솔더의 미세 구조분석)

  • 이충식;김영호;권오경;한학수;주관종;김동구
    • Journal of the Korean institute of surface engineering
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    • v.28 no.2
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    • pp.67-76
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    • 1995
  • The microstructure of 95wt.%Pb/5wt.%Sn and 63wt.%Sn/37wt.%Pb solders for flip chip bonding process has been characterized. Solders were deposited by thermal evaporation and reflowed in the conventional furnace or by rapid thermal annealing(RTA) process. As-deposited films show columnar structure. The microstructure of furnace cooled 63Sn/37Pb solder shows typical lamellar form, but that of RTA treated solder has the structure showing an uniform dispersion of Pb-rich phase in Sn matrix. The grain size of 95Pb/5Sn solder reflowed in the furnace is about $5\mu\textrm{m}$, but the grain size of RTA treated solder is too small to be observed. The microstructure in 63Sn/37Pb solder bump shows the segregation of Pb phase in the Sn rich matrix regardless of reflowing method. The 63Sn/37Pb solder bump formed by RTA process shows more uniform microstructure. These result are related to the heat dissipation in the solder bump.

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The Changes of Pectic Substances and Enzyme Activity, Texture, Microstructure of Anchovy Added Kimchi (멸치 첨가 김치의 숙성 중 펙틴 함량, 효소 활성, 조직감과 미세구조의 변화)

  • 송영선;류복미;전영수;문갑순
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.25 no.3
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    • pp.470-477
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    • 1996
  • This study was intended to observe the changes of pectic substances and enzyme activities, texture, microstructure of anchovy added kimchi during fermentation for 4 weeks at 4$^{\circ}C$. Content of alcohol insoluble solid(AIS) and HCl soluble pectin(HClSP) were decreased, whereas content of hot water soluble pectin(HWSP) was increased during fermentation. Content of HClSP was higher and HWSP was lower in anchovy added kimchi than control. Activity of pectinesterase(PE) was decreased, whereas activity of polygalacturonase(PG) was increased during fermentation. In anchovy added kimchi, PG activity was lower than control. Changes in microstructure of Chinese cabbage and kimchi during fermentation was lower than control. Changes in microstructure of Chinese cabbage and kimchi during fermentation was observed ; in the raw cabbage, parenchyma cells, intercellular space and middle lamella were clearly shown. But in salted cabbage, middle lamella became separated. In the late stage of fermentation, parenchyma cell walls were wrinkled and collapsed. Puncture forces of kimchi were decreased, whereas cutting forces of kimchi were increased as fermentation proceeded. The firmness was slightly higher in anchovy added kimchi than control at the late stage fermentation, which may be explained by the PG activity.

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