热暴露对表面预形变单晶合金组织和性能的影响

Effect of Thermal Exposure on the Micro-structure and Performance of Surface Pre-deformed Single-crystal Superalloy

摘要:

针对[001]取向的DD11单晶合金,垂直于[001]方向进行两种强度的铸钢弹丸喷丸强化以引入表面预形变,采用电子背散射衍射(EBSD)、扫描电镜和硬度等方法研究了预形变后表层组织；后续热暴露完成后,采用扫描电镜和硬度计,研究了热暴露温度和预形变程度对表层组织和硬度梯度的共同影响；并且表征了喷丸+热暴露后单晶合金的高温疲劳性能。结果表明,单晶合金喷丸预形变后表面出现[110]和[111]取向的亚晶,同时出现表面应变硬化效果；随着形变程度的增大,亚晶取向角、旋转亚晶层深度和硬化效果也随之增大。随着热暴露温度升高,预形变表面形变组织呈现球化-零星不连续胞状组织-连续胞状组织-再结晶的动态回复过程,硬化效果也随之松弛；形变程度越大,在越低的温度下开始出现动态回复过程,但喷丸+1060℃/2h热暴露并未观察到再结晶。相比磨削状态,喷丸+热暴露后1060℃轴向疲劳寿命有所提高。1060℃/350MPa/r=-1/轴向疲劳源呈现内部萌生为主源,表面为次源的状态。

关键词:单晶合金;热暴露;喷丸;预形变;表层组织

Abstract:

[001] oriented DD11 single-crystal superalloy (SC) was shot-peened perpendicular to [001] to induce pre-deformation. Pre-deformed micro-structure was investigated using elecron backscatter diffraction (EBSD), scanning electron microscopy (SEM) and micro-hardness tester (HT). After subsequent thermal exposure (TE), the effect of the temperature and pre-deformation degree on surface structure was researched by SEM and HT, moreover, high-temperature fatigue performance after peening-exposure was tested. The results show that after pre-deformation, [110] and [111] oriented subgrains were observed on the surface, and that surface strain hardening effect occured. The greater the deformation degree was, the larger the subgrain orientation angle, the depth of the rotating subgrain layer and the hardening effect were. With the increase of exposure temperature, the pre-deformed surface micro-structure showed a relaxion of micro-hardness and a dynamic recovery process of spheroidization, fragmentation-discontinuous cellular organization and continuous cellular organization. Furthermore, the greater the deformation degree was, the lower temperature the recovery process occured at. However, the recrystallization was not observed at the condition of shot peening and 1060℃/2h. Compared with grinding and TE, the 1060℃ fatigue cycles increased while peening and TE. For fatigue condition 1060℃/350MPa/r=-1/axic, the main source of fatigue is sprouting inside, while secondary source is born on the surface.

Key words:Single-crystal superalloy; thermal exposure; shot peening; pre-deform; Surface micro-structure