Creep deformation and fracture of DZ40M cobalt-base superalloy at intermediate temperature

Creep deformation and fracture of directionally solidified cobalt-base superalloy DZ40M have been investigated at 700°C under stress with the scope of 360-340 MPa. The creep fracture surfaces and longitudinal sections of crept specimens have been examined by SEM and the deformed microstructures have been observed under TEM. The results showed that there was a linear relationship between transient creep strain (εβ) and creep time t^1/3, and steady creep rate(ε̇) could be expressed as ε̇ = Aexp(bσ/kT) where, A=8.7270 x 10^-13 %h^-1, b=0.9039 x 10^-21 cm³. DZ40M alloy exhibited high creep ductility. In the matrix, a great amount of fine M₂₃C₆ carbide precipitated that strengthened the alloy matrix effectively. Creep cracks initiated at primary carbides and interfaces between the carbides and the matrix. Cracks propagated transgranularly at the direction perpendicular to the applied stress.