Papers by Author: Ben Jiang Qian

Abstract: By means of calculating stacking fault energy (SFE), measuring creep properties and contrast analysis of dislocation configuration, an investigation has been made into the influence of the stacking fault energy on the creep mechanism of the single crystal nickel-based superalloy. Results show that the alloy at 760¡æ has a lower stacking fault energy (SFE), and the SFE of the alloy increases with the temperatures. The deformed mechanism of the alloy during creep at 760¡æ is the cubical γ′ phase sheared by <110> super-dislocation which may be decomposed to form the configuration of (1/3)<112> super-Shockley partials dislocation plus the superlattice intrinsic stacking fault (SISF). The deformed mechanism of the alloy which possesses the higher SFE at 1070¡æ is the screw or edge super-dislocation shearing into the rafted γ′ phase. The SFE of the alloy at 980¡æ is intervenient between the ones of 760¡æ and 1070¡æ, the deformation mechanism of the alloy during creep is the rafted γ′ phase sheared by <110> screw and edge super-dislocations which may be decomposed into the configuration of (1/2)<110> partial dislocation plus APB.

Abstract: By the measurement of creep curves and microstructure observation, an investigation has been made into the creep behaviors and microstructure evolution of a single crystal nickel-based superalloy containing 4.2%Re. Results show that the superalloy displays an obvious sensibility on the applied temperatures and stresses in the range of the applied temperatures and stresses. During the initial creep, the cubical g¢ phase in the alloy is transformed into an N-type rafted structure along the direction vertical to the applied stress axis. After crept up to fracture, the rafted g¢ phase in the region near fracture is transformed into a twisted configuration. The dislocation climbing over the rafted g¢ phase is considered to be the main deformation mechanism of the alloy during the steady creep state, and dislocations shear into the rafted g¢ phase is the main deformation mechanism of the alloy in the later stage of creep.

Abstract: By means of the finite element method (FEM) for calculating the von Mises stress and strain energy density in the cubic γ/γ′ phases, the regularity of γ′ phase directional growth is investigated. Results show that the change of the strain energy density in the different planes of the cubical γ′ phase occurs during tensile creep of alloy, the cubical γ′ phase is directionally grown, along the crystal plane with bigger strain energy, to transform into the mesh-like rafted structure along the direction perpendicular to the applied stress axis. The change of the atomic potential energy, interfacial energy and lattice misfit stress is thought to be the driving force for promoting the elements diffusion and directional growth of γ′ phase.

Abstract: An investigation has been made into the microstructure and creep behaviors of [110] oriented single crystal nickel-base superalloy. Results show that, after a full heat treated, the cubic  phase is coherently embedded in the matrix and regularly arranged along the <100> orientation. During creep, the cubic phase in the alloy is transformed into the rafted structure lying 45 relative to the direction of the applied stress. Under the condition of the applied stress of 137 MPa at 1040°C, the alloy displays a higher strain rate and shorter creep lifetime. The deformation mode of the alloy during creep is dislocations activated within the matrix channels and the rafted phase. Dislocation slip activated easily on the Roof-type channel is thought to be the main reason of the alloy having higher strain rate and shorter creep lifetime.

Abstract: By means of the calculation of the elements diffusion mobility, an investigation has been made into the influence of the elements interaction on the rates of the elements diffusion and  phase directional coarsening during creep of single crystal superalloys. Results show that the elements diffusion and  phase directional coarsening during creep are related to the applied stressed and elastic modulus. And the rate of  phase directional coarsening is enhanced with the applied stresses. Due to the interaction between the elements, the rates of the elements diffusion and  phase directional coarsening decrease with the increment of the elements Ta+Mo gross and Ta/W ratio. In the diffusion field of the elements during creep, the Al, Ta atoms with bigger radius are diffused to {100} planes to form the N-type rafted structure along the direction vertical to the applied stress axis, and the change of the strain energy density in the interfaces of the cubic  phase is thougth to be the driving force of the elements diffusion.