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

针对[001]取向的DD11单晶合金,在垂直于[001]方向进行2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)、扫描电镜和硬度测试等方法研究了预形变后表层组织;后续不同温度热暴露完成后,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,开始出现动态回复过程的温度越低,但喷丸+1060℃/2 h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℃/350 MPa/R=–1/轴向疲劳源呈现内部萌生为主源,表面为次源的状态。

The [001] oriented DD11 single-crystal superalloy(SC) was shot-peened perpendicular to [001] to induce pre-deformation.Pre-deformed microstructure was investigated using electron backscatter diffraction(EBSD), scanning electron microscopy(SEM) an d microhardness tester(HT). After subsequent thermal exposure(TE) at different temperatures, the effect of the temperature and pre-deformation degree on surface structure and microhardness profile was researched by SEM and HT, and the high-temperature fatigue performance after peening-thermal exposure was tested. The results show that after pre-deformation, [110] and [111] oriented sub-grains are observed on the surface, and surface strain hardening effect occurs. The greater the deformation degree, the larger the sub-grain orientation angle, and the greater the depth of the rotating sub-grain layer and hardening effect. With the increase of exposure temperature,the pre-deformed surface microstructure shows a dynamic recovery process of spheroidization, fragmentation-discontinuous cellular organization and continuous cellular organization, and the micro-hardness is relaxed. Furthermore, the greater the deformation degree, the lower the temperature at which the recovery process occurs. However, no recrystallization is observed under the condition of shot peening+1060 oC/2 h. Compared with grinding and TE, the 1060 oC fatigue cycles increase after peening and TE. For fatigue condition of1060 oC/350 MPa/R=?1/axic, the main source of fatigue is sprouting inside, while secondary sources appear on the surface.