IN-SITU STRENGTHENING OF TITANIUM WITH YTTRIUM

In situ processing consists of heavily deforming a two-phase alloy of mutually immiscible elements to produce composite sheet or wi re. In the well-studied Cu (fcc)-Nb (bcc) system, severe deformation by swaging and drawing reduces niobium filament phase thicknesses from 1-5 mu m (as-cast) to 0.007-0.030 mu m (after deformation). Cu-20% (vol.) Nb ultimate tensile strengths exceed 2000 MPa for material deformed to a true strain of eta=12, where eta=In (area(original)/area(final)). In a study on in situ strengthening in immiscible hexagona I close-packed metals, Ti-50 wt % Y and Ti-20 wt % Y alloys were deformed by hot extrusion, hot swaging, and cold swaging. As deformation progressed, samples were taken for tensile testing and examination by SEM and TEM. Ti-Y alloys deformed to final true strains of 6.6 (Ti-50Y) and 7.6 (Ti-20Y) contain nanofilaments (100 nm phase spacing) similar to those of deformation-processed Cu-20Nb at comparable strains. The ultimate tensile strengths of the alloys approximately tripled as deformation progressed from the as-cast condition to these final true strains, although the exponential strength increase seen in Cu-Nb alloys was not observed.