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Alloy ordering and spinodal decomposition of the microscopic phase field simulation

Author: ZhangYanHong
Tutor: ZhuJingChuan
School: Harbin Institute of Technology
Course: Materials Science
Keywords: Homogeneous transformation Spinodal decomposition Ordering Microscopic phase- field equations Iron-based alloys
CLC: TG131
Type: Master's thesis
Year: 2008
Downloads: 106
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Abstract


In this thesis, microscopic phase field method of binary iron-based alloys ordered with three yuan iron-based alloy spinodal decomposition process, and on this basis, combined with microscopic theory of elasticity and the discrete lattice in the form of micro-diffusion equation studied the elastic energy for ordering and spinodal decomposition behavior. This model can be used to study the precipitation of binary and ternary substitutional alloys common problems, without pre-set the new phase structure and phase transition paths, automatic describing the possible non-equilibrium phase, cluster together and so the whole process and all inclusive precipitation composition range. Ordering of binary alloys and post-coarsening process simulation showed that: does not consider the elastic distortion energy, when the alloy composition is less than stoichiometric composition, the first large-scale discrete ordered phase appears to be disorderly spaced, then ordered phase gradually Unicom, a growing area; solute diffusion of atoms from the disordered phase to an ordered phase, so that poor solute atoms disordered phase region, while the ordered phase concentration, increasing the degree of ordering, Finally ordered phase coarsening; when components higher than the stoichiometric composition, the diffusion of solute atoms from the ordered phase to the disordered phase, along with the disorder enrichment of solute atoms. Consider the elastic distortion energy, the precipitation process more rearward, the elastic distortion can affect the morphology of low concentration alloy more obvious. Particles and the relative position between the particles is no longer maintained random state, but looming directionality tends along the flexible \Ordered phase while the concentration curve and the long program parameters were analyzed, the results showed that the elastic strain energy has hindered the process of ordering, but did not change the evolutionary mechanism. On the ternary alloy spinodal decomposition and post-coarsening process simulation shows that, without considering the elastic strain energy, the decomposition depends on the material organization-specific morphology of the initial composition: In the three-component composition equal to or have a very low component ingredients to form a majority the matrix phase, a small spherical phase is isolated tissue; remaining ingredients to form a three-phase element are each three phase tissue, two-phase α, β are enriched with discrete black particles are present in the marginal region γ matrix. Discrete two-phase precipitation sequence depends on the initial composition: the high concentration of component instability starts first, with the instability after the precipitates, coarsening grew up phase and the post-buckling instability first phase occurred \Another limiting surface meet the growth phase. After adding elastic strain energy, phase particles precipitated from the original discrete distribution equiaxed particles gradually to irregular granular changes. With the increase of elastic strain energy, the faster the spinodal decomposition occurs, the more dispersed particles. Spinodal decomposition of binary alloys with similar elastic strain energy increases accelerated the spinodal decomposition progresses.

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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 > Alloy theory
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