TEM STUDY OF B-CONTAINING AND ER-CONTAINING DISPERSOIDS IN RAPIDLY SOLIDIFIED DISPERSION-STRENGTHENED TITANIUM AND TITANIUM ALUMINIDE ALLOYS

The structure of B- and Er-containing dispersoids in rapidly sotidified, dispersion-strengthened Ti-0.5at%Er, Ti-6at%B, Ti-25at%Al-0.5at%Er, Ti-25at%Al-4at%B, Ti-48at%Al-0.5at%Er, and Ti-48at%Al-5at%B was examined by TEM. Rapid solidification was achieved using the electron beam melting/splat quenching technique, and the specimens were annealed at 800-degrees-C, 1000-degrees-C and 1200-degrees-C in vacuo for 1 hour. Boron added to Ti and Ti-25at%/Al reacted with the matrix to form faceted TiB dispersoids with well-defined orientation relationships. The dispersoids had a semi-ordered sequence of planar faults parallel to TiB(020) planes. Boron in Ti-48at%Al reacted to form faceted TiB2 dispersoids which are randomly oriented with respect to the matrix. The erbium-containing alloys displayed 100-500 nm diameter, spheroidal, incoherent precipitates of Er2O3. However, in Ti-48at%Al-0.5at%Er, Er2O3 precipitates smaller than 50 nm were observed by HRTEM to form with a distinct orientation relationship, and in some cases a semi-ordered fault structure. When Ti-48at%Al-0.5at%Er was heated above 1000-degrees-C, a new Er-Ti-O phase formed, with a distinct habit and morphology.