Date of Award
Doctor of Philosophy
Materials Science and Engineering
L. Scott Chumbley
New composites have been developed by mechanically working mixtures of immiscible, ductile metals to severe deformations to reduce the two metals' phase thicknesses to the order of 10[superscript]-2 [mu]m. Many deformation processed composites have been produced using cubic metals. These composites are crystallographically textured filamentary microstructures with unusually high ultimate tensile strengths (UTS) and high ductility;This study produced a deformation processed composite using two hexagonal close packed (hcp) immiscible metals, Ti and Y. A 75mm diameter ingot of Ti containing 20% by volume Y was cast and deformation processed by extrusion, swaging, and wire drawing to true strain 12.8. A similar ingot of pure Ti was cast and deformation processed to true strain 10.0 as a control specimen. Both compositions were annealed at 700°C. after every 60% reduction in area and examined by gas fusion analysis, tensile testing, x-ray texture analysis, optical microscopy, SEM, and TEM as the deformation progressed;The Ti and Y phases both developed the \langle 10[macron]10\rangle fiber texture typical of low c/a ratio, drawn hcp metals. Crystals so textured must deform by plane strain, and the Ti and Y filaments acquired a ribbon shape as the deformation processing narrowed and elongated each phase. These ribbon-shaped filaments bent around one another as each crystal accommodated the plane strain of neighboring crystals;As the deformation processing true strain increased from 0 to 7.27, the average phase thickness decreased from 13[mu]m to 0.36[mu]m for the Ti and from 2.9[mu]m to 0.084[mu]m for the Y. At true strains greater than 7.27, the filamentary microstructure recrystallized to a fine-grained, equiaxed structure. At true strain 12.2, the resulting equiaxed structure had an average grain diameter of 0.20[mu]m and 698 MPa UTS. The applicability of various mathematical models developed to characterize cubic deformation processed alloys is discussed with respect to this hcp composite, and a potentially strong hcp-hcp sheet composite is proposed to employ the plane strain in these textured phases to best advantage.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Alan Mark Russell
Russell, Alan Mark, "Microstructure-strength relationships of a deformation processed titanium-yttrium composite " (1994). Retrospective Theses and Dissertations. 10505.