材料期刊网

研究了一种[011]取向镍基单晶合金的拉伸蠕变特征及其变形期间的微观组织结构. 结果表明: 在750 ℃/680 MPa条件下, 合金的初期蠕变和稳态蠕变速率相对较高, 蠕变寿命较短. TEM观察显示, 蠕变期间的变形特征是1/2<110>位错在基体中运动, 发生反应形成1/3<112>超 Shockley不全位错切入γ´相后产生层错; 在870 ℃/500 MPa条件下, 蠕变中期出现不均匀滑移带并有大量超不全位错剪切γ´相, 使合金具有较高的应变速率; 在980 ℃/200 MPa条件下, 合金具有较长的蠕变寿命和较低的稳态蠕变速率. 不同Burgers矢量的位错相遇发生反应形成界面位错网, 位错网可以阻止位错切入γ´相, γ´相沿[010]方向扩散生长, 逐渐转变成筏形组织. 蠕变后期位错切入γ´相, 是合金变形的主要方式.

The creep behavior of a Ni base single crystal superalloy with [011] orientation under three conditions of temperature and stress level has been investigated. Creep deformation of the tested alloy occurs largely through dislocation activity in the γ matrix channel. Shearing of the γ´ precipitates is observed, while at higher temperature, this does not occur until late in life by means of the passage of superpartial dislocation.  At lower temperature (750 ℃) and high stress level, shearing of the  γ´ precipitates is observed in the relatively early creep through the passage of 1/3<112> dislocation, which leaves superlattice stacking faults (SSFs) in the precipitates. The creep behavior is closely related to microstructure evolution, the creep curve at 750 ℃ exhibits higher primary and steady creep rates, and thereby the creep life is shorter. Under the condition of 870 ℃ and 500 MPa, the steady-stage creep does not appear, it is suggested that the creep life is greatly influenced by the inhomogeneous slip band. At higher temperature and lower stress, such as 980 ℃ and 200 MPa, the alloy has longer creep life and lower steady creep rate. Observation of the dislocation configuration shows that the hexagonal dislocation network appears on the  γ/ γ´ interface at the early creep stage, the regular and denser dislocation networks can inhibit dislocation cutting into  γ´ phase and enhance the resistance of dislocation movement. In the later stage, $\gamma'$ precipitates are sheared by dislocation, which leads to an acceleration of creep rate.