[011]取向镍基单晶合金蠕变特征

CREEP CHARACTERISTICS OF A Ni BASE SINGLE CRYSTAL SUPERALLOY WITH[011]ORIENTATION

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, γ′ precipitates are sheared by dislocation, which leads to an acceleration of creep rate.