A refined fully lamellar TiAl alloy extruded at α-phase region: Microstructure and mechanical properties

Abstract

Multiphase TiAl alloys with refined fully lamellar (RFL) microstructure can balance their mechanical properties at room temperature (RT) and high temperatures, which is vital for their applications. A new cost-effective and compact processing method is needed to reduce the processing cost and widen the extent of applications. In this work, Ti–44.5Al–4Nb–0.5Mo–0.1B (at.%) alloy with RFL microstructure was fabricated using a one-step hot-pack extrusion process at 1280 °C with an extrusion ratio of 4. The microstructure and mechanical properties of the extruded rod were uniform except in a thin layer near the surface. The RFL microstructure exhibited a deformation texture with <11 2‾ 0> α2 parallel to the extrusion direction and (0001) α2 parallel to the radial direction of the rod. The yield strength, ultimate tensile strength and ductility of the rod were simultaneously improved after extrusion due to elimination of βo phase, decrease in the sizes of the lamellar colony and spacing, and the presence of texture. The fundamental reason why RFL microstructure can be obtained by extrusion is that the higher Al and lower Mo contents in the alloy expand α phase region and decrease βo content of the alloy compared with TNM alloy.