摘要
针对航空发动机高压压气机叶片超高周疲劳寿命不足的问题,结合薄叶片宏观变形控制要求,采用微尺度激光冲击强化工艺提高了叶片超高周疲劳性能。采用62 mJ冲击能量和1次冲击(62 mJ&1 time)、62 mJ冲击能量和3次冲击(62 mJ&3 times)、82 mJ冲击能量和1次冲击(82 mJ&1 time)三种工艺参数对GH4169合金进行了微尺度激光冲击处理,在常温条件下进行了应力比为-1的轴向超声疲劳试验,通过扫描电子显微镜(SEM)和能量色散光谱仪(EDS)分析了断口形貌,通过激光扫描共聚焦显微镜(CLSM)、X射线衍射仪(XRD)和电子背散射衍射仪(EBSD)分析了微尺度激光冲击对表面形貌、残余应力和微观组织的影响,揭示了抗疲劳强化机理。试验结果表明:三种工艺参数均可提高GH4169合金的超高周疲劳性能,且冲击次数、冲击能量的增大有利于超高周疲劳性能的进一步提高。当疲劳寿命达到1×10~8次循环时,62 mJ&3 times试样承受的循环应力幅(500 MPa)最大,相较于未进行微尺度激光冲击的试样,提高了25%。微尺度激光冲击在表层400~500μm范围内引入了最大-761 MPa的残余压应力、细化晶粒及高密度位错,表面裂纹萌生和早期扩展得到了抑制,因此超高周疲劳性能得到提高。
Objective GH4169 is a nickelbased superalloy widely used in manufacturing aeroengine blades.However,it is affected by ultrahigh cycle fatigue due to the low impact energy and small spot diameter of microscale laser shock peening.To address these issues,microscale laser shock peening reinforcement is employed to improve the fatigue properties of the material while controlling the depth of propagation of the shock wave to achieve macrodeformation of the thin blades and synergistic enhancement of fatigue properties.Currently,the effect of microscale laser shock peening on the ultrahigh cycle fatigue properties of GH4169 alloy has not been investigated in domestic and international studies.Consequently,this effect is investigated in this study using an ultrasonic fatigue testing machine.Methods In this study,GH4169 alloy was used,and the fatigue specimen size was obtained through theoretical design and simulation.The specimens were subjected to microscale laser shock peening using three process parameters:62 mJ impact energy and 1 time impact(62 mJ&1 time),62 mJ impact energy and 3 times impacts(62 mJ&3 times),and 82 mJ impact energy and 1 time impact(82 mJ&1 time).Subsequently,axially symmetric ultrasonic ultrahigh cycle fatigue tests were conducted at room temperature,and fatigue fracture morphologies were analyzed using scanning electron microscope(SEM)with energydispersive spectroscope(EDS).Confocal laser scanning microscopy(CLSM)was used to analyze the surface morphologies strengthened by microscale laser shock peening,while Xray diffraction(XRD)analysis was used to determine the distribution of residual stress in the surface layer.Additionally,the microstructure of the surface layer after microscale laser shock peening was observed using electron backscatter diffraction(EBSD).The analytical results were synthesized to reveal the strengthening mechanism of microscale laser shock peening in improving the ultrahigh cycle fatigue properties of GH4169 alloy.Results and Discussions The SN curves(Fig.4)indicate that microscale laser shock peening improves the ultrahigh cycle fatigue properties of GH4169.Fatigue fracture morphologies(Figs.5‒8)show that slip induces crack initiation,while microscale laser shock peening inhibits surface crack initiation.Additionally,surface morphology analysis(Figs.9 and 10)reveals that microscale laser shock peening increases surface roughness.However,fatigue test results show that the increase in surface roughness due to laser shock peening is not the primary factor affecting the failure mechanism and properties of ultrahigh cycle fatigue.Combining fatigue test results with surface residual stress distribution data(Fig.11)indicate that the residual compressive stress introduced by microscale laser shock peening inhibits surface crack initiation.Furthermore,a combination of fatigue test results and microstructure EBSD analysis(Figs.12 and 13,Table 4)reveals that refined surface grains and highdensity dislocations contribute to fine grain and dislocation strengthening,respectively,thereby improving the ultrahigh cycle fatigue properties of the material.Conclusions In this study,the influence of microscale laser shock peening on the ultrahigh fatigue properties of GH4169 alloy is investigated using ultrasonic fatigue tests combined with the analysis of the fracture morphologies,surface morphologies,residual stress,and microstructure.This comprehensive approach enables a detailed understanding of the strengthening mechanism of microscale laser shock peening in improving the ultrahigh cycle fatigue properties of GH4169 alloy.The main conclusions are as follows:microscale laser shock peening improves the ultrahigh cycle fatigue properties of GH4169 alloy,allowing the material to withstand higher stress amplitudes at the same fatigue life.When the fatigue life reaches 1×108 cycles,62 mJ&1 time,62 mJ&3 times,and 82 mJ&1 time specimens endure cyclic stress amplitudes of 450,500,and 475 MPa,respectively,representing increases of 12.5%,25%,and 18.75%.Microscale laser shock peening improves surface roughness,with Ra values of 0.926,1.020,and 0.935μm for 62 mJ&1 time,62 mJ&3 times,and 82 mJ&1 time specimens,respectively.Increasing the impact energy and the numbers of impacts increases surface roughness but does not contribute to surface fatigue failure.Microscale laser shock peening introduces residual compressive stress within a depth range of 400‒500μm,with a gradient distribution.The 62 mJ&3 times specimen exhibits a maximum residual compressive stress of-761 MPa below the surface.Additionally,microscale laser shock peening refines grains of the surface layer and increases dislocation density,reducing the average diameters of the surface grains to 5.23,4.09,and 4.68μm,respectively.The average kernel average misoreintation(KAM)values of the surface layer reach 0.25°,0.29°,and 0.27°,respectively,while the geometrically necessary dislocation(GND)densities increase to 0.78×1014,0.9×1014,and 0.85×1014/m²,respectively.After microscale laser shock peening,the sources of fatigue cracks in GH4169 alloy shift from the surface to the interior because the residual compressive stress suppresses surface crack initiation and effectively balances the tensile stress.Additionally,surface layer grain refinement and the introduction of highdensity dislocations contribute to fine grain and dislocation strengthening,respectively,further inhibiting surface crack initiation and improving the fatigue properties of the material.
作者
李岱桦
何卫锋
聂祥樊
吴宇航
潘吉乐
Li Daihua;He Weifeng;Nie Xiangfan;Wu Yuhang;Pan Jile(National Key Lab of Aerospace Power System and Plasma Technology,School of Aviation Engineering,Air Force Engineering University,Xi’an 710038,Shaanxi,China;National Key Lab of Aerospace Power System and Plasma Technology,Xi’an Jiaotong University,Xi’an 710038,Shaanxi,China)
出处
《中国激光》
北大核心
2025年第12期61-72,共12页
Chinese Journal of Lasers
基金
国家自然科学基金(52205240)。
