Creep Behavior And Deformation Mechanism Of Single Crystal Nickel-Based Superalloy With Different Orientations

In the paper, by means of measurating of creep curves and microstructure observation, an investigation has been made into the microstructure evolution regularity of the single crystal superalloy with different orientations during creep, and the influence of the crystal orientations on the creep behaviors of the single crystal nickel base superalloy.Results show that the regular"+"dendritic morphology is displayed in the cross-section of single crystal nickel base superalloy with [001] orientation, and the longer and shorter dendritic are displayed in the cross-section of [011]orientation alloy along the vertical and horizontal directions, and the asymmetry distribution of the dendritic directions along the 60o and 120o angles arrangment is displayed in the cross-section of [111] orientation alloy. After fully heat treated, the microstructure of the superalloys with [001], [011] and [111] orientations consists of that the cubicγ′phase is regularly arranged along the <100> directions, thereinto, the cubicγ′phase in the [011] orientation superalloy is arranged along the direction of 45o angle on (100) crystal plane, and the strip-like raftedγ′phase is formed along [001] orientation during creep. and theγmatrix phase is continuously filled between the raftedγ′phase. The cubicγ′phase in the superalloy with [111] orientation is arranged along the direction of 53o angle on (1?21) plane. During tensile creep, the meah-like raftedγ′phase is formed [111] orientation alloy along the direction of 35o angle on the (?101) plane.The creep lifetimes of the superalloy with [001], [111] and [011] orientations reduce in turn, under the condition of 1040℃/137MPa. Compared to the [011] and [111] orientations alloys, [001] orientation alloy displays a better creep resistance and longer creep lifetime under the conditions of high and intermediate temperatures. In the range of the experimental temperatures and stresses, the strain rates of the superalloys with [001], [011] and [111] orientations during steaty state creep obey to Dorn rate equation. In the further, the activation energies of the superalloys with [001],[011] and [111] orientations are calculated to be Q[001] = 469.56kJ/mol, Q[011] = 396.54 kJ/mol and Q[111] = 411.12kJ/mol respectively, and the stress exponents are calculated to be n[001] =4.77,n[011] =4.10 and n[111] =5.56 respectively. The dislocation climbing over theγ′raft phase is thought to be the deformed mechanism of the alloy with [001] orientation during the steady state creep. In the later stage of creep, the deformed mechanism of the alloys with [001] and [011] orientations is <110> super-dislocation shearing into the raftedγ′phase. Significant amount of dislocations appear in the [111] orientation alloy during creep due to the bigger strain, which result in the form of the subgrain as creep goes on.In the later stage of creep, the microcracks are initiated in the interfaces of the raftedγ′/γphase in the [011] and [111] orientations supperalloy, and propagated on the interfaces of the raftedγ′/γphase along the direction vertical to the applied stress axis as creep goes on, which is thought to be the fracture mechanism of the alloys during creep.