Boyd, Robert (1975) Crystal growth and plasticity of vanadium disilicide. PhD thesis, University of Warwick.

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Abstract

Vanadium disilicide (VSi₂) has been studied as a model with a view to evaluation disilicides as high temperature structural materials. The homogeneity range and phase boundaries of VSi₂-x have been determined. Evidence has been obtained for the existence of a "new" phase in the V-Si binary system, and a new V-Si phase diagram, including this information, is presented.

Large high-purity single crystals with compositions across the homogeneity range of VSi₂-x have been grown by Czochralski pulling from a melt contained in a cold hearth r.f. levitation crucible. A compression testing programme was carried out on these crystals in the temperature range 600-1200°C. Analysis of the compressed crystals by optical metallography and transmission electron microscopy showed that in the temperature range studied VSi₂ deformed by basal slip only. Defect structure consisted typically of paired dislocations which were shown to be mainly dislocation dipoles. A model for plasticity in VSi₂ has been proposed. Slip is initiated by overcoming of a Peierls barrier. There is a two-stage work-hardening curve. Stage I (high) hardening is due to dipole formation. Stage II is a region in which a dynamic recovery process occurs by dislocation climb and annihilation of loops formed from dipoles. Experimental evidence from temperature, composition and strain rate dependence has been used to justify this model.

The lack of slip flexibility in VSi₂ emphasises that it will be difficult to prepare an engineering material to fully utilise the good strength retention and oxidation resistance at high temperatures found in disilicides. However, the use of disilicides either in the form of very fine-grained polycrystalline material or as the fibrous phase (with the c-axis as the fibre axis) in a ductile (metallic) matrix has been suggested as the most promising potential use for transition metal disilicides as structural materials.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QA Mathematics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Crystal growth, Plasticity, Vanadium
Official Date:	December 1975
Dates:	Date Event December 1975 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Lewis, M. H. (Mike H.)
Sponsors:	Science Research Council (Great Britain) ; Lucas Industries Limited
Extent:	101 leaves
Language:	eng

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