采用预压应力处理使镍基单晶合金中的γ’相转变成P-型筏状结构, 通过拉伸蠕变曲线测定和组织形貌观察, 研究了该合金拉伸蠕变中的组织演化. 结果表明: 在拉伸蠕变初期, 合金中的P-型筏状γ’相转变为N-型筏状结构. 由于高温拉应力导致γ’/γ两相中元素平衡浓度发生变化及P--型筏状γ’相的不均匀粗化, 促使P-型筏状γ’相发生分解出现沟槽; 沟槽区域溶质元素化学位的提高引起的元素定向扩散是γ’相逐渐溶断成类立方体结构的主要原因. 切应力分量使立方γ’相与应力轴垂直界面的晶格收缩可排斥较大半径的Al和Ta原子, 拉伸张应力使平行于应力轴界面的晶格扩张可诱捕较大半径的Al和Ta原子, 是促使γ’相定向生长成为N--型筏状的主要原因. 其中, 在拉应力作用下类立方γ’相不同界面的应变能密度变化是元素扩散及γ’相定向粗化的驱动力.
By means of pre-compression treatment, the cubic γ′phase in the single crystal nickel-base superalloy is transformed into the P-type rafted structure. An investigation has been into the microstructure evolution of the P-type rafted structure alloy during tensile creep by means of the measurement of creep curve and microstructure observation. Results show that the P-type rafted γ′phase in the alloy is transformed into the N-type structure in the initial stages of the tensile creep. In the role of the tensile stress at high temperature, the change of the elements equilibrium concentration occurs in the γ′/γ phases, which promotes the unhomogeneous coarsening of the γ′phase, and in the further the decomposition of the P-type rafted phase occurs in the alloy to appear the groove structure. It is a main reason of the directional diffusion of the elements and dissolving abruption of the P-type rafted γ′phase up to transformed into the cuboidal-like structure that the enhancement of the chemical potential energy of the solute elements occurs in the groove regions of the P-type γ′rafted structure. And then, the lattice constriction in the horizontal interfaces of the cuboidal-like γ′phase may repel out the Al, Ta atoms with bigger radius due to the role of the shearing stress, the lattice expanding in the side interfaces of the cuboidal-like γ′phase may trap the Al, Ta atoms with the bigger radius in the role of the tension stress, which promotes the directional growing of γ′phase into the N-type rafted structure. Thereinto, the change of the strain energy density in different interfaces of the cuboidal-like γ′phase is thought to be the driving force of the elements diffusion and the γ′phase directional growth.
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