| Popis: |
In �-? titanium alloys, the high-temperature ? phase can decompose in several ways, depending on alloy composition and cooling rate. In the case of welded joints, cooling rates can vary widely as a function of heat input. In the current work, a dilute �-? Ti-Al-Mn alloy was welded over a range of heat inputs using electron beam and gas tungsten-arc welding processes. A major part of the rapidly cooled electron beam weld could be identified as lath-type or "massive" martensite. In the slower cooled gas tungsten-arc welds, the transformation product was a mixture of lamellar � and ? phases formed entirely by diffusion. Post-weld heat treatment resulted, in all cases, in an �-? structure that coarsened with annealing temperature and time. Tensile elongation in the as-welded condition was poor on account of a large prior-? grain size and an acicular microstructure. The ductility improved as the structure coarsened on heat treatment. Tensile fracture was always microscopically ductile, but the presence of a grain boundary � layer tended to induce intergranular rupture, especially when a hard, intragranular matrix confined slip to occur in the grain boundary regions. ? 1998 Chapman & Hall. |
