Ta、Ti对镍基单晶高温合金中γ和γ′相元素分配行为的影响OA

The microstructure of γ′ phase,the γ/γ′ lattice misfit,and partitioning behavior of alloying elements in four Ni-12.5%Al-8.31%Co-6.25%Cr-1.06%Mo-2.06%W-x Ta-(3.12%-x)Ti(x=0,1.04%,2.08%,3.12%,atomic fraction)alloys were investigated using a scanning electron microscope,X-ray diffraction,a scanning transmission electron microscope,and first-principles calculations.The results show that as u/v(where u presents the atomic content of Ta,and v represents the sum of Ta and Ti atomic contents)increases from 0 to 1,the shape parameter of γ′phase gradually decreases from 0.54 to 0.46.The absolute value of lattice misfit decreases from 0.245%to 0.198%.When u/v=0.66,the γ′ phase reaches its maximum average size(233 nm)and volume fraction(74.8%).In all four alloys,Al,Ta and Ti have a preference for the γ′ phase,while Cr,Mo and Co prefer to the γ phase.In contrast,W elements exhibit a transition from initial preference for the γ'phase into the γ phase.Except for Co,other elements tend to partition to the γ'phase.However,due to the stronger partitioning driving force of Ta and W,Cr and Mo are displaced into the γ phase.In addition,compared with W,Ta possesses a higher partitioning driving force,leading to part of W being displaced into the γ′ phase and resulting in an"inverse partitioning"phenomenon of W.