Compressive creep behavior of selective electron beam melted high Nb containing TiAl alloy

In this study, the compressive creep behavior of Ti-45Al-8Nb alloy fabricated by selective electron beam melting technology at 800 degrees C and 850 degrees C was investigated. This alloy is mainly composed of equiaxed gamma grains, and minor alpha 2 and B2 grains. Creep results show that compressive creep behavior of this alloy is dependent on temperature, which is manifested in the significant increase of creep strain and creep rate with the increase of temperature. Through a multi-step creep test, the stress exponent n (2.65 at 800 degrees C and 3.65 at 850 degrees C) and activation volume V* (36.49 b3 at 800 degrees C and 53.51 b3 at 850 degrees C) were measured. Combined with kinetic analysis based on n and V* and TEM observation, compressive creep deformation of this alloy at 800 degrees C and 850 degrees C is dominated by dislocation motion, including dislocation slip and climb. Additionally, mechanical twinning also plays an important role in creep deformation. Driven by dislocation pile-ups or mechanical twins, discontinuous dynamic recrystallization (DDRX) occurs during creep. The degree of DDRX at 850 degrees C is greater. Sufficient DDRX greatly softens the alloy and accelerates creep rate, resulting in no steady-state creep stage at 850 degrees C.