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Effect of Growth Rate on Coarsening of Secondary Dendrite Arm Spacings in Directionally Solidified of Al-8.8La-1.2Ni Ternary Alloy

Üstün Erkan, Çadirli Emin

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 3

931--938

EN

One of the most important factors directly affecting microstructure and mechanical properties in directional solidification process is secondary dendrite arm spacing (SDAS). It is very important to measure the SDAS and examine the factors that may affect them. To investigate the effect of growth rate on the SDAS, the alloy specimens were directional solidified upward with different growth rates (V = 8.3-83.0 μm/s) at a constant temperature gradient (G = 4 K/mm) in a Bridgman-type growth apparatus. After the specimens are directionally solidified, they were exposed to metallographic processes in order to observe the dendritic solidification structure on the longitudinal section of the specimens. Coarsen secondary dendrite arm spacings (λ2C) were measured excluding the first arms near the tip of the dendrite. Local solidification times ( tf) were calculated by ratio of spacings to growth rates. It was determined that the tf values decreased with increasing V values. The relationships between tf and λ2C were defined by means of the binary regression analysis. Exponent values of tf were obtained as 0.37, 0.43, 0.46 and 0.47 according to increasing V values, respectively. These exponent values are close to the exponent value (0.33) predicted by the Rappaz-Boettinger theoretical model and good agreement with the exponent values (0.33-0.50) obtained by other experimental studies.

2

Preparation Of Fine Grained SiC At Reduced Temperature By Two-Step Sintering

Kim K.-W., Oh K.-S., Lee H., Kim B. S., Chung T.-J.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1539--1542

EN

Two-step sintering route was applied for the densification SiC by promoting the role of liquid phase. The specimen contained 8 vol% of liquid phase composed of Al2O3 and Y2O3. The heating schedule consisted with initial rapid heating to 2000°C and immediate quenching to 1700 or 1750°C. By heating at elevated temperature, even distribution of the liquid phase was intended. The heat treatment at reduced temperature was to suppress the evaporative loss of the liquid and to secure the time for densification. The two-step sintering effectively suppressed loss of mass and coarsening. The resultant SiC was thus dense and was composed of fine grains exhibiting hardness of 2321 kgf/mm2.

3

A phase-field model for multi-component and multi-phase systems

Moelans N.

Archives of Metallurgy and Materials

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2008

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Vol. 53, iss. 4

1149-1156

EN

An alternative phase-field model is presented for the simulation of microstructure evolution in polycrystalline materials existing of multiple phases and components. The model is able to treat concurrently phase transformations, diffusion controlled coarsening (Ostwald ripening) and grain growth. The eąuilibrium phase fractions and compositions are introduced using appropriate thermodynamic Gibbs energy expressions. Furthermore, the model allows to specify the energy and mobility, and their anisotropy, for each interface individually and the diffusion properties of the different phases. Simulation results are discussed for the coarsening of a simplified Cu/Cu-Sn solder joint with Cu6Sn5-precipitates.

PL

Przedstawiono alternatywny model pól fazowych zastosowany do symulacji zmian mikrostruktury w materiałach polikrystalicznych w układach wielofazowych i wieloskładnikowych. Zaproponowany model uwzględnia jednocześnie przemiany fazowe oraz kontrolowany dyfuzyjnie rozrost ziaren (tzw. dojrzewanie Ostwalda). Przedstawiono i przedyskutowano wyniki uproszczonej symulacji przeprowadzonej dla połączenia lutownego Cu/Cu-Sn z wydzieleniem Cu6Sn5.