粉末合金FGH95喷丸强化对高温缺口疲劳性能的影响

Effect of Shot-Peening on High-Temperature Notched Fatigue Property of FGH95 Powder Metallurgy Superalloy

为提高粉末合金材料轮盘应力集中结构的缺口疲劳性能,采用铸钢弹丸、陶瓷弹丸和复合喷丸的方法对粉末合金缺口旋转弯曲疲劳试样进行喷丸强化,通过白光干涉表面形貌分析、配合电化学腐蚀的X射线衍射残余应力场分析、显微硬度梯度研究评价喷丸强化层状态;采用高温旋转弯曲缺口(结构应力集中系数Kt=1.7)疲劳寿命进行对比分析。结果表明,喷丸强化在FGH95合金表面形成强化层:表面粗糙度Ra=0.9～1.5μm,Kurtosis值R_(ku)接近3的表面轮廓;表面压应力在–800～–1150MPa,压应力场深度达到120～250μm;相比于基体硬度的480～510HV_(0.2),喷丸后表面硬度上升到575～625HV_(0.2),硬化层深度达到175～250μm。采用首次喷铸钢丸大强度、第二次喷陶瓷丸小强度的二次喷丸工艺方法时,表层残余压应力场数值大,表面硬化程度高且硬化层深度大,表面粗糙度较小且弹坑底部圆滑,疲劳强化效果最佳,550MPa/650℃中值疲劳寿命估计量较原始提高20倍以上。

To promote the fatigue property of the disk’s stress-concentration structure made by powder metallurgy superalloy,cast-iron shots,ceramic beads and the compound of the two kinds of shots are employed to peen the PM notched fatigue sample.Strengthening layer is characterized by surface profile analysis using white light interfere,residual stress measurement with X-ray diffraction and electrochemical corrosion,and micro-hardness profile research.Fatigue strengthening effect is compared with high-temperature notched (structure stress-concentration coefficient Kt=1.7) fatigue life of rotating-bending mode.The results show that strengthening layer is introduced by shot peening on the surface of FGH95 alloy.After shot peening,the surface average roughness and Kurtosis value are 0.9–1.5μm and close to 3 respectively.Surface residual stress is about –800 – –1150MPa,and the depth is 120~250μm.Moreover,compared with the as-received hardness 480–510HV0.2,the peening surface hardness increased to 575–625HV0.2,and the hardness layer depth is 175–250μm.The double shot peening method,firstly using the cast-iron shot in big intensity and secondly using the ceramic shot in small intensity,brings the maximum residual compressive stress,the highest hardness and biggest depth on the surface,and the smaller roughness with smooth bottom of crater,which obtains the best fatigue strengthening effect.The median fatigue life estimations of the double shot peening at 550MPa/650℃ is 20 times higher than original one.