孔挤压强化对Inconel 718高温合金疲劳性能的影响

为了提高Inconel 718高温合金螺栓连接孔的疲劳抗力,研究了孔挤压强化对Inconel 718高温合金中心孔试样疲劳寿命的影响,并采用扫描电镜、粗糙度仪、X射线应力测量仪及金相显微镜等仪器对孔壁表面完整性进行分析,探讨了孔挤压强化机制。结果表明:1.90%挤压过盈量的中心孔试样的中值疲劳寿命是未强化试样中值疲劳寿命的1.16~4.79倍。与2.85%挤压过盈量的试样相比,1.90%挤压过盈量试样取得了更优的疲劳寿命增益效果。分析发现:经1.90%挤压过盈量的孔挤压强化后,孔壁表面完整性得到了显著改善,孔壁表面粗糙度下降了64.2%,孔边形成了较深的残余压应力场,孔边晶粒组织发生了明显的塑性变形,形成了组织强化层。表面完整性的改善对疲劳寿命的增益具有重要作用。

Effects of Hole Cold Expansion on Fatigue Property of Inconel 718 Superalloy

To improve the fatigue resistance of the bolt connecting hole, experimental research was carried out to investigate the effect of hole cold expansion (HCE) on the fatigue life of Inconel 718 superalloy. The fatigue fracture, surface roughness, residual stress, and microsturcture of the hole wall were characterized by scanning electron microscopy(SEM), roughmeter, X-ray diffraction(XRD) instrument and optical microscopy. The mechanism of the HCE on the fatigue life was also investigated. The results show that the predicted median value of fatigue life of the HCE specimens with an expansion ratio of 1.90% is about 1.16-4.79 times larger than that of the non-expansion specimens. The fatigure performance of the specimens with 1.90% was better than that of the specimens with 2.85%. The surface integrity of the hole wall is improved after the HCE with 1.90%, the roughnesss decreases by 64%, and the deep surface strengthened layer and residual compressive stress field are formed around the hole through the severe plastic deformation of the microstructure of the hole-wall surface. The improvement of surface integrity plays an importance role on the enhancement of the fatigue life.