• Title/Summary/Keyword: $\gamma$',$\gamma$"and $\delta$precipitate

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The Evaluation of Diffusivity of Lithium for Coarsening of δ' Precipitate in AI-Li-Cu-Mg-Zr Alloy (Al-Li-Cu-Mg-Zr 합금에 있어서 δ'상 조대화를 위한 Lithium의 확산계수 평가)

  • Chung, D.S.;Kim, E.S.;Cho, H.K.
    • Journal of the Korean Society for Heat Treatment
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    • v.7 no.1
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    • pp.17-24
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    • 1994
  • The evaluation and analysis of diffusivity of lithium for coarsening and coarsening kinetics of ${\delta}^{\prime}$ precipitate in Al-Li-Cu-Mg-Zr alloy aged at $170^{\circ}C$ have been investigated by transmission electron microscopy. With ageing time, ${\delta}^{\prime}$ precipitate coaesened to followed $\bar{\gamma}{\propto}t^{1/3}$ and coarsening kinetics was found to be obeyed to the Lifshitz-Slyozov-Wagner(LSW) theory and diffusivity of lithium for coarsening of ${\delta}^{\prime}$ precipitate in Al-Li-Cu-Mg-Zr alloy was obtained to be $5.85{\times}10^{-17}{\sim}1.53{\times}10^{-16}$ by experimental coarsening rate constant and various coarsening kinetic theory. Diffusivity of lithium measured by using various model but MLSW and Tsumuraya (VI) et al. model in Al-Li-Cu-Mg-Zr alloy is similar to that calculated by the Costas's diffusivity equation. It was, therefore, suggested that additing to the Cu, Mg and Zr element in Al-Li system have no great effect on diiffusivity of lithium for coarsening of ${\delta}^{\prime}$ This suggest that in matrix.

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Effect of Heat Treatment on the Microstructures of Inconel 718 Superalloy (INCONEL 718 초내열 합금의 열처리에 따른 미세조직 변화)

  • Choi, J.H.;Lee, K.R.;Jo, C.Y.;Kim, I.B.
    • Journal of the Korean Society for Heat Treatment
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    • v.5 no.2
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    • pp.85-94
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    • 1992
  • Microstructural evolution of wrought Inconel 718 superalloy with different heat treatment conditions was studied. Heat treatment was performed via conventional(CHT), modified(MHT), Merrick(MeHT) and modified Merrick (MMeHT) methods. The size of ${\gamma}^{\prime}$ and ${\gamma}^{\prime\prime}$ precipitates which are principal strengthening phases in Inconel 718 superalloy increase in order of CHT, MHT, MeHT. For the case of MMeHT, a coexistence of fine ${\gamma}^{\prime\prime}$ precipitate and very coarse particles due to exess growth of ${\gamma}^{\prime\prime}$, which is called bimodal distribution, was observed. CHT gave the finest grain size. (Ti, Nb)C carbide and needle-like ${\delta}$ phase were formed together at grain boundaries for CHT, and were formed both inside and at boundaries of grains for MHT, MeHT and MMeHT. Morphology of partially serrated grain boundaries was developed in all heat treatment conditions except CHT.

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Effect of Precipitates on the High Temperature Tensile Properties of Cast Alloy 718 (주조용 718합금의 고온 인장 성질에 미치는 석출물의 영향)

  • Ju, Dong-Won;Jo, Chang-Yong;Kim, Du-Hyeon;Ryu, Yeong-Su;Kim, In-Su;Jo, Hae-Yong;Choe, Seung-Ju
    • Korean Journal of Materials Research
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    • v.10 no.7
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    • pp.515-521
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    • 2000
  • The effect of precipitates on the high temperature tensile properties of cast alloy 718 was investigated by phase extraction method and microstructural observation. The value of tensile strength and elongation gradually decreased with increasing testing temperature up to $760^{\circ}C$. Elongation of the alloy increased, while tensile strength decreased above 76$0^{\circ}C$. The amount of precipitates in the specimen that tensile tested at $760^{\circ}C$ showed maximum owing to stress assisted precipitation. Therefore, the alloy exhibited the lowest value of the elongation and the degree of decrease in yield strength at this temperature due to high flow stress of precipitates. Little amount of precipitate, especially $\gamma$' and $\gamma$", resulted in softening of the alloy at the temperature above $760^{\circ}C$.

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Influence of the Cooling Rate on the Phase Precipitation of Super Duplex Stainless Steel (슈퍼 듀플렉스 스테인리스강의 응고·냉각 시 상석출에 미치는 냉각속도의 영향)

  • Jang, Eun Seok;Kim, Ki Young;Kim, Suk Jun
    • Journal of Korea Foundry Society
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    • v.35 no.2
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    • pp.23-28
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    • 2015
  • This work presents the effect of the cooling rate on the precipitation of super duplex stainless steel. Specimens of super duplex stainless steel with a specific composition were cooled at various cooling rates after being melted at $1550^{\circ}C$ in a directional solidification furnace. Ferrite (${\delta}$), Austenite (${\gamma}$), Sigma (${\sigma}$), and Chi (${\chi}$) phases were precipitated when the cooling rate was lower than 0.22 K/s. When the cooling rate was 0.22 K/s or faster, ${\sigma}$ and ${\chi}$ phases were not precipitated.

A Study on the Electrical Conductivity of $Na_2O-Fe2O_3-B_2O_3-P_2O_5$ System Glass ($Na_2O-Fe2O_3-B_2O_3-P_2O_5$ 계 유리의 도전성에 관한 연구)

  • 박용원;이경태
    • Journal of the Korean Ceramic Society
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    • v.22 no.3
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    • pp.35-40
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    • 1985
  • The composition of the base glass was determined to be $Na_2O$ 15, $Fe_2O_3$ 35, $B_2O_3$ 0~20, $P_2O_5$ 30~50 by mole percent. The heating temperature for nucleation was determined by means of thermal expansion curve. Crystalline phases were investigated by X-ray diffraction method and I.R Spectra. Electrical conductivities of glass spec-imens were observed in the temperature range 25~20$0^{\circ}C$ The activation energies of these specimens were caculated. The results obtained were as follows : 1) The limit composition of the melts 15mol% $Na_2O$ 35mole% $Fe_2O_5$ 20mole% $B_2O_3$ 30mole% $P_2O_5$ was able to be formed into desired shapes during cooling, . 2) In the measurement of d. c conductivity($\delta$) on the glasses in the system $15Na_2O-35Fe_2O_3$-$B_2O_3$-(50-x) $P_2O_5$ the values decreased by replacing 5 mole% $P_2O_5$ with $B_2O_3$ 3) The d. c conducties of heat treated samples were increased by replacing $P_2O_5$ with $B_2O_3$ 4) $B_2O_3$ contributed to precipitate crystals such as${\gamma}$-$Fe_2O_3$ $Fe_3O_4$ which had the advantage of electronic conduction in heat treated samples. 5) The slope plotted Log($\delta$) versus 1/T in this glass system was linear in the measured temperature range.

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