The Connection Between Orientation And Evolution Of Microstructure In A Cr Rich Nickel Based Single Crystal Superalloy

The Ni-based single crystal(SC) superalloy is the major material fabricating blade used in aircraft engine. The SC superalloy has excellent high temperature strength, oxidation resistance and corrosion resistance which can service at harsh conditions. During the deformation process of Ni-based SC superalloy, the orientation determines the activated number of slip system, leading to different deformation rate, which will further influence the service life of superalloy. Much studies have indicated that the [001] oriented alloy showing the best high temperature performance. Therefore, it is important to guarantee the [001] orientation to ensure the service life of the alloy. During creeping process, the orientation of alloy will be changed(reorientation) because of the restriction effect applied on the two ends of the sample and the movement of dislocations. Understanding the reorientation mechanism is important to control the orientation and mechanical properties of alloy. However, the intrinsic mechanism of the reorientation is unclear, i.e. the relationship between the reorientation and the microscopic structure. In this study, a new type of Cr-riched SC superalloy was chosen to investigate the reorientation caused by creeping and aging. The relationship between the reorientation and microstructure evolution were revealed.The subjects of this study are to reveal:(1) The orientation of crystal, having strong effect on the mechanical properties, might varies during creep testing, can lead to the operation of the {111}<112> slip system or not. The formation mechanism of the <112> partial dislocations, shearing into the ?? phase.(2) The defects shearing into the g? phase can proceed in two manners, the extended dislocation(one 1/3<112>, one 1/6<112> partial dislocation and the stacking fault between them) and the dislocation pair(two 1/2<110> full dislocation). However, the activation of these two mechanism was unclear.(3) What is the effect of temperature acts on the orientation.The study concluded that:(1) <112> partial dislocations come from the reaction of <110> full dislocation, and this reaction exists the intermediate process;(2) The determinant factor of the shearing of g? by extended dislocation or dislocation pair, is the accumulated dislocation at the g?/g interface are the same type or not;(3) The effect of temperature can make the specimen deviated from the original orientation, and the changment can't fully recover after the cooling, after the short-time aging treatment at 950 °C, the oriented concentration of the whole sample is getting stronger.Besides, the study further discovered: although the orientation will be changed, and the oriented deviation between different regions can be enlarged during the creep process, while they all distribute near the [001] direction; the size and morphology of g? phase remain unchanged during the creep process of 750 oC/750 MPa.