INTERPHASE BOUNDARY PRECIPITATION IN A TI-1.7 AT. PCT ER ALLOY

Microstructures in a Ti-1.7 at. pct Er alloy were studied in the are-c ast, rapidly solidified, and annealed conditions. Transmission electro n microscopy (TEM) of the rapidly solidified materials revealed 3- to 20-nm-diameter precipitates that were distributed in regularly spaced, approximately planar Sheets throughout equiaxed alpha Ti grains. The precipitate sheet morphology is similar to the interphase boundary car bide sheets that have been documented in many alloy steels. In additio n, precipitate fibers with cross sections of approximately 5 nm and up to 500 nm in length were often found adjacent to particle sheets. Ele ctron diffraction experiments showed that the structure and lattice sp acings of the sheet and fibrous particles are consistent with elementa l erbium. Subsequent annealing treatments resulted in the formation of a face-centered cubic allotrope of Er2O3. The present work describes the precipitate morphologies and crystallography and discusses the app licability of current ledge growth models of interphase boundary preci pitation to titanium-erbium alloys.