CREEP DEFORMATION AND FRACTURE OF DZ40M DIRECTIONALLY SOLIDIFIED COBALT-BASE SUPERALLOY AT HIGH TEMPERATURE
(Institute of Metal Research, The Chinese Academy of Sciences,Shenyang110015, P. R. China；
ShenyangPolytechnic University, Shenyang110023, P. R. China)
ShenyangPolytechnic University, Shenyang110023, P. R. China)
Abstract: The creep deformation and fracture of DZ40M directionally solidified cobalt-base superalloy have been investigated at 900℃under stress in the range of 105~125 MPa. The microstructures, fractures and substructures of crept specimens have been examined by SEM and TEM. The results showed that DZ40M alloy exhibits a high creep ductility and its stress dependence of steady state creep rate is of a typical feature of precipitation hardened alloys, its creep behaviour is closely related to microstructural change. During creep, the primary carbides M7C3and MC dissolved and the secondary M23C6carbide profusely precipitated, which strengthens the matrix effectively. Creep cracks initiate at the primary carbides and propagate transgranularly. The surface of specimens was oxidized severely and the preferential oxidation of the primary carbides deteriorated creep rupture strength.
Key words: directional solidification cobalt-base superalloy creep fracture