Microstructure and viscosity of semi-solid mixtures

The semi-solid state of metallic alloys is characterized by the coexistence of solid and liquid phases at thermal equilibrium. The rheology of such diphasic materials not only depends on the solid fraction, but also is highly correlated with the degree of aggregation of the solid particles. The visc...

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Bibliographic Details
Published in:Journal of physics. Condensed matter 2000-03, Vol.12 (12), p.2567-2577
Main Authors: Barbé, J C, Perez, M, Papoular, M
Format: Article
Language:English
Subjects:
Applied sciences
Condensed matter: structure, mechanical and thermal properties
Cross-disciplinary physics: materials science
rheology
Defects and impurities in crystals
microstructure
Deformation
material flow
Engineering Sciences
Exact sciences and technology
Materials
Metals. Metallurgy
Physics
Rheology
Structure of solids and liquids
crystallography
Viscoplasticity
yield stress
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Summary:The semi-solid state of metallic alloys is characterized by the coexistence of solid and liquid phases at thermal equilibrium. The rheology of such diphasic materials not only depends on the solid fraction, but also is highly correlated with the degree of aggregation of the solid particles. The viscosity eta of a diphasic (30% and 40% solid fractions) Ag-Cu alloy was measured using a contactless method: at 923 deg C, we get eta = (2 plus /minus 1) mult 10 exp 3 Pa s for a solid fraction of 30% and eta = (2 plus/minus 1) mult 10 exp 4 Pa s for a solid fraction of 40%. The solid, copper-rich phase, is dispersed into globules of about 50 mu m in size. The large value of eta suggests that these particles form a random interconnected network. This type of microstructure is likely to give rise to the thixotropic rheological properties of many semi-solid materials. The structure and therefore the viscosity are sensitive to the applied shear rate gamma . Two distinct regimes of aggregation, depending on the actual value of the shear rate, are discussed: 'compact clusters' versus 'random network'. We calculate the characteristic size of the compact clusters and discuss the parameters governing the state of aggregation.
ISSN:0953-8984
1361-648X
DOI:10.1088/0953-8984/12/12/301