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Title: Crystal growth and plasticity of vanadium disilicide
Author: Boyd, Robert
ISNI:       0000 0001 3473 9223
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1975
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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.
Supervisor: Not available Sponsor: Science Research Council ; Lucas Industries Limited
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QA Mathematics ; QD Chemistry