IN-SITU STRENGTHENING OF TITANIUM WITH YTTRIUM - TEXTURE ANALYSIS

In situ processing consists of heavily deforming a two-phase alloy of mutually immiscible elements to produce composite sheet or wire. In th e well-studied Cu(fcc)-Nb(bcc) system, severe deformation by swaging a nd drawing reduces as-cast Nb filament phase thicknesses several hundr ed-fold after deformation. Cu-20 vol % Nb ultimate tensile strengths e xceed 2000 MPa for material deformed to a true strain of eta = 12, whe re eta = In (area(original)/area(final)). In an earlier study of in si tu strengthening in immiscible hexagonal close-packed metals, Ti-50 vo l % Y and Ti-20 vol % Y alloys were deformed by hot extrusion, hot and cold swaging. The composites were deformation processed to true strai ns as high as eta = 7.6 to form a filamentary microstructure with fila ment thicknesses on the order of 0.1 mu m. The deformation processing of these composites increased their ultimate tensile strengths from 31 8 to 945 MPa, but the specimens' original diameters were too small to allow deformation processing to the very high true strains achieved wi th the Cu-Nb composites. In this study, a larger casting of Ti-20 vol % Y was deformation processed to eta = 12.8 in an attempt to achieve f urther refinement of the filament thickness. This composite formed the same filamentary microstructure up to eta = 7.27 observed in the earl ier study of Ti-Y composites; however, at higher eta values the filame nts recrystallized into equiaxed grains, decreasing the ultimate tensi le strength. X-ray texture analysis of the composite specimens showed a strong [<10 (1)over bar 0>] fibre texture in both the Ti and Y phase s in the deformation processing range 2.25 less than or equal to eta l ess than or equal to 7.27. This texturing is thought to constrain both the Ti and Y phases to deform by plane strain, which produces severe geometric restrictions on the ability of the plane straining filaments to achieve high eta values without fracturing or recrystallizing.