孔挤压强化对FGH95合金室温及高温疲劳性能的影响

Effect of Hole Cold Expansion on Fatigue Property of FGH95 Superalloy Under Room and High Temperature

孔是一种典型的应力集中结构。本文研究了芯棒直接冷挤压对FGH95合金试样中心孔的高、低温疲劳寿命的影响规律,并采用扫描电镜、粗糙度仪、X射线应力测量仪及显微硬度计等仪器分析了疲劳断口和孔壁表面完整性主要参数,探讨了FGH95合金孔挤压强化机制。结果表明:相比未挤压试样,孔挤压试样在室温、650MPa的中值疲劳寿命提高了0.9倍以上,而527℃、575MPa的中值疲劳寿命提高了10.3倍以上。分析表明,孔壁经冷挤压后,孔壁表面粗糙度大幅下降,孔壁沿径向形成了一定深度的残余压应力层和组织硬化层,对中心孔试样的室温、高温疲劳寿命的提升具有重要作用。另外,晶界的存在和相邻晶粒的晶体学取向差异会对疲劳裂纹扩展路径产生显著的影响。

Hole is widely considered as a kind of geometrical-discontinuous structure with high stress or strain concentration.The effect of direct hole cold expansion(HCE)using the mandrel on the fatigue behaviour of centre holes of FGH95 superalloy was investigated.The fatigue fracture and the main parameters of surface integrity of hole wall were characterized by scanning electron microscopy(SEM),roughmeter,X-ray diffraction(XRD)instrument and microhardness tester.The mechanism of the HCE on the fatigue life was also investigated.The results show that the median fatigue life of the HCE specimens increased by above 0.9 times and 10.3 times under room temperature/650MPa and 527℃/575MPa conditions compared to the specimen without HCE,respectively.It is found that the roughnesss of hole wall decreased sharply,while the deep surface strengthened layer with high hardness and residual compressive stress were formed around the hole after HCE.These changes are of great benefit to the enhancement of the fatigue life under room and high temperature.In addition,the exit of grain boundary and the difference of crystallographic orientation of neighbor grains have an evident effect on the fatigue crack growth path.