• High Al/Nb content in Ti-46Al-8Nb alloy suppresses B2 phase formation, enhancing creep resistance.
• The alloy exhibits power-law creep with activation energy 274 kJ/mol and stress exponent 1.97, indicating grain boundary sliding as the dominant mechanism.
• Irregular serrated grain boundaries improve creep resistance by hindering dislocation movement, while smooth boundaries are prone to crack initiation.
• Cracks initiate within lamellar structures under stress concentration and propagate along boundaries perpendicular or at 45° to the stress axis, leading to failure.