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Evolution Of Multivariant Microstuctures With Anisotropic Misfit

Electronic Theses of Indian Institute of Science

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Title Evolution Of Multivariant Microstuctures With Anisotropic Misfit
 
Creator Bhattacharyya, Saswata
 
Subject Metallography
Anisotropy
Metal Alloys
Multivariant Microstructures
Microstructural Evolution
Dynamic Growth Shapes
Anisotropic Misfit
Isolated Precipitate
Metallurgy
 
Description Many technologically important alloys such as Ni base superalloys and Ti-Al base alloys benefit from the precipitation of an ordered β phase from a disordered α matrix. When the crystallographic symmetry of the β phase is a subgroup of that of the disordered α phase, the microstructure may contain multiple orientational variants of the β phase, each with its own (anisotropic, crystallographically equivalent) misfit (lattice parameter mismatch) with the matrix phase. Examples include orthorhombic precipitates in a hexagonal matrix in Ti-Al-Nb alloys, and tetragonal precipitates in a cubic matrix in ZrO2-Y2O3.
We have studied two-phase microstructures containing multiple variants of the precipitate phase. In particular, we have used phase field simulations to study the effect of elastic stresses in a two dimensional system containing a disordered matrix and three different orientational variants of the precipitate phase, with a view to elucidate the effect of different levels of anisotropy in misfit.
We consider a two dimensional, elastically homogeneous and isotropic model system in which the matrix (α) and precipitate (β) phases have hexagonal and rectangular symmetries, respectively, giving rise to three orientational variants of the β phase. Therefore, our phase field model has composition (c) and three order parameters (η1, η2, η3) as the field variables.Due to the difference in crystallographic symmetry, the precipitate-matrix misfit strain tensor, ε*, can be anisotropic. ε*maybe represented in its principal form as

ε *= (ε xx 0 )
0 εyy
where ε xx and ε yy are the principal components of the misfit tensor.
We define t= εyy/εxx as the parameter representing anisotropy in the misfit. In this thesis, we report the results of our systematic study of microstructural evolution in systems with different values of t, representing different levels of anisotropy in misfit:
•Case A: t=1 (dilatational or isotropic misfit)
• Case B: 0
 
Contributor Abinandanan, T A
 
Date 2009-06-17T04:43:20Z
2009-06-17T04:43:20Z
2009-06-17T04:43:20Z
2007-11
 
Type Thesis
 
Identifier http://hdl.handle.net/2005/532
 
Language en_US
 
Relation G22201