Different tensile and compressive creep behaviours in a fully lamellar Ti–44Al–1Mn–2.5Nb–0.15Gd alloy

Creep behaviour of a Ti–44Al–1Mn–2.5Nb–0.15Gd alloy was investigated in both tension and compression. The alloy was cast and heat treated to have a fully lamellar microstructure with an average grain size of ∼265 μm. Creep tests were conducted in vacuum at 750 °C and under constant stresses between 100 and 400 MPa. The normal three stage creep was observed in both tension and compression with a well-defined steady state. However, the steady state creep rate in tension was significantly higher than that in compression. The microstructure after creep deformation exhibited lattice dislocations forming well-defined network in tension and dislocation bow-out and straight lattice dislocations in compression in the ‘soft’ grains and individual dislocations and twins in the ‘hard’ grains.