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Precipitate Behavior of γ’ Phase in Ni-Al Alloys with the Internal Elastic Strain

Author: ChengXiaoLing
Tutor: LiYongSheng; WangLinTao
School: Nanjing University of Technology and Engineering
Course: Materials Engineering
Keywords: Ni-Al alloys Precipitation Phase-field Microstructure Coarsening
CLC: TG132.32
Type: Master's thesis
Year: 2013
Downloads: 44
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Abstract


Ni-based superalloys are widely used in the aerospace field owing to their excellent strength, toughness, fatigue performance, oxidation and thermal corrosion performance at high temperatures. The strength of Ni-Al alloy depends on the volume fraction, size, morphology and spatial distribution of γ’ phase. Thus, the research of γ’ morphology evolution and the coarsening behavior of γ’ phase are essential for improving performance of alloy.Based on the Phase-field model and microscopic elastic theory, by using the periodic boundary conditions, Ginzburg-Landau and Cahn-Hilliard kinetic equation is solved with a semi-implicit fourier-spectral method. With Matlab7.0programming, We investigated the effects of the internal elastic strain, composition and temperature on the microstructure evolution and coarsening behavior of γ’ phase in Ni-Al alloys.Under the internal strain induced by the lattice mismatch, ordered γ’ phase particles in Ni-18at.%Al alloy change their shape from sphere to cubes, and then to strongly aligned rectangular shape along the [10] and [01] directions in the Ni-Al alloy. The ordering of γ’ phase is faster than the compositing equilibrium.With the increase of the Al concentration, the morphology of precipitated phase changes from separated cuboidal to connected rectangle shape. The γ’ phase constantly growing up, coarsening and connection. Meanwhile, the composition, ordering and volume fraction of γ’phase change faster, However, the coarsening rate decrease. The influence of internal elastic strain plays a main role in the γ’ phase coarsening process.With the decrease of the aging temperature, the γ’ phase morphology changes from separated cuboidal to connected rectangle shape. The γ’ phase constantly growing up, coarsening and connection. The composition, ordering and volume fraction of y’phase change faster. The coarsening rate of γ’ phase decreases.The average particle size of γ’ phase as a function of time follows a cubic growth law of LSEM theory under the elastic interaction. Elastic stress will decelerate growing up and coarsening process of γ’ phase.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Special physical properties of alloys > Special thermal properties of alloys > Melting point alloys , refractory alloy , high temperature alloys
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