材料期刊网

分别制备了[001]和[011]取向的Ni-Co-Cr-Mo-W-Al-Ti-Ta镍基单晶高温合金试样. 在 750 ℃/750 MPa条件下, [001]取向合金的平均蠕变寿命明显高于[011]取向合金, [011]取向合金延伸率稍高. 在982 ℃/248 MPa条件下, [001]取向合金的平均蠕变寿命和延伸率均高于[011] 取向合金, 各向异性主要表现在加速蠕变阶段, 但各向异性程度比低温高应力时显著降低. 在高温低应力条件下, 2种取向合金中γ´相均已形筏, [001]取向合金的筏化方向垂直于应力轴, 而[011]取向合金的筏化方向与应力轴的夹角约为45°. γ´相形筏后, 阻碍了位错运动, 导致加工硬化, 因此,  γ´ 相筏化是各向异性程度降低的主要原因. 在[011]取向合金的蠕变后期观察到孪晶组织同时穿越 γ和 γ´相, 导致试样塑性大幅度降低, 迅速断裂.

Constant load creep tests were performed on the [001] and [011] oriented Ni-Co-Cr-Mo-W-Al-Ti-Ta single crystal superalloys. The [001] oriented alloy has much longer creep life than that of [011] oriented alloy, but the elongation of [011] oriented alloy is slightly higher under the condition of 750 ℃/750 MPa. The average creep life and elongation of [001] oriented alloy are both higher than that of [011] oriented alloy at 982 ℃/248 MPa, and the anisotropy occurs mainly during the accelerating creep stage, but anisotropic degree decreases obviously. The SEM analysis revealsγ ´phases are rafted in the two directions, which blocks the glide/climb of dislocations and causes creep hardening, the rafting of γ´ phase is the dominant reason to decrease of creep anisotropy at higher temperature. The TEM observation indicates deformation twins formed in [011] oriented alloy, which lowers the plasticity of the sample and induces the sample to fracture rapidly.