Grain refinement of Ti₂AlNb-based alloy through canned multi-directional forging

Ti₂AlNb-based intermetallic alloy has a great potential application in the manufacturing of aeronautical structures. However, the casted ingots of this alloy often consist of very coarse grains even as large as in centimetre level. The refinement of the coarse grain by hot deformation is essential for prompting this material to the engineering applications. In this work, multi-directional isothermal forging (MDIF) was conducted on Ti-20Al-24Nb at 1200°C and 1050°C with 2, 4, 6, 8 and 10 cycles, and a comparative study was emphasized on the grain refinement by two different reductions (30% and 40%) in each compression. The microstructure evolution has been systematically investigated. Results show that dynamic recrystallization (DRX) occurred preferentially near grain boundary, and very large strains were required to refine B2 grains. For 40% reduction per compression, the recrystallization volume fraction after four cycles was more than 95%, and the grain size was evenly refined from centimetre level to ~250μm. However, for 30% reduction per compression, the original coarse grains still exist after 10 cycles, and the recrystallization is far from complete, although the total strain is much greater than the process by using 40% reduction but with fewer cycles. The results demonstrate that the grain refinement of this material depends mainly upon the height reduction per compression and the deformation temperature and the magnitude of deformation or strain is not the critical factor to determine the recrystallization.