Precipitate crystallography and morphology in undercooled, rapidly solidified titanium rare earth alloys

Previous investigations of rapidly solidified titanium-rare earth alloys show supersaturated martensitic alpha ' Ti microstructures that are essentially devoid of precipitates in the as-quenched condition. In contrast, as-quenched Ti-Ce, Ti-Er and Ti-La alloys with large bulk liquid undercoolings just prior to rapid solidification contain dispersions of 3-20 nm diameter elemental rare earth particles within equiaxed alpha Ti grains. Electron diffraction experiments indicate that the precipitates are semi-coherent metallic rare earths. In the Ti-Ce and Ti-Er alloys, particles are arranged in planar and curved sheets. These are the first observations of this precipitate morphology in a Ti-Er alloy. Annealed materials contain both semi-coherent elemental rare earth particles and semi-coherent rare earth oxide particles with structures and orientation relationships that are unique to this undercooling/rapid solidification study.