Effect Of Laser Shock Peening On Surface Integrity And Fatigue Life Of GH4169

Nickel-based superalloy GH4169 has been commonly used in the manufacture of turbines in the aerospace industry,due to its high strength,creep resistance and long fatigue life in high temperature environment above 600 ?.The blades of the turbine rotor are subjected to severe thermal and mechanical loads under service conditions,and the blade roots are extremely susceptible to cracking due to stress concentrations.The processing of the GH4169 needs to be improved due to high service life of turbine rotor blades.The blade disc structure of the turbine rotor is special,and the root processing technology is difficult to be optimized.Laser shock peening technology has the advantages of good strengthening effect,strong controllability and good adaptability.Small-spot laser impact has the advantages of economy and stability.Therefore,small-spot laser shock peening can be used to improve the surface quality and fatigue strength of GH4169.In this paper,the effect of small-spot laser shock peening on the surface integrity and fatigue life of GH4169 is studied.The small-spot laser shock peening test platform is built based on the principle of laser shock peening and shock wave theory model.The laser shock peening GH4169 experiment,tensile fatigue test,finite element simulation and mathematical statistics analysis are combined to analyze the surface residual stress,microhardness and roughness of GH4169 with different overlap rates,energy densities and impact times.The formation mechanism of GH4169 surface integrity influenced by small-spot laser shock is explored.The quantitative relationship between the process parameters of small-spot laser and the fatigue life of GH4169 is revealed.The mapping relationship between the surface integrity and the fatigue life of GH4169 is analyzed.Firstly,the effects of laser shock process parameters on the surface integrity of GH4169 processing are studied.Based on the principle of laser shock peening,the small-spot laser shock peening test platform is set up.The laser shock test,the residual surface stress diffractometer,Vickers hardness tester and laser confocal microscope are combined with the mathematical statistics analysis method to quantitatively evaluate the surface integrity of GH4169.The experimental results show that the residual stress and microhardness of the surface of the GH4169 are increased with the increase of the number of laser impacts.The residual stress of the machined surface is graded along the depth of the surface of the GH4169 sample.The roughness Ra of the machined surface is firstly increased and then decreased and then increased with the increase of the overlap rate.Secondly,the finite element simulation model of small-spot laser shock peening alloy GH4169 is established based on shock wave theory model.The residual stress distribution of GH4169 after laser shock peening with different overlap rates and energy densities is obtained by simulation analysis.Compared with the test data obtained by laser shock reinforced GH4169 experiment,the residual compressive stress obtained by simulation and experiment has the same trend with the depth of the surface of GH4169 sample.The results show that finite element simulation can effectively predict the small spot laser with different overlap rates.Finally,the effect of laser shock peening on the low cycle fatigue life of GH4169 is studied.The low-cycle fatigue failure test of the axial load of GH4169 laser shock-strengthened sample shows that the fatigue life of GH4169 sample is obviously improved after the laser shock peening under the same energy density.The change with the increase of the overlap rate is not obvious.At the same overlap rate,the low cycle fatigue life of GH4169 is increased with the increase of the energ)y density.The fracture morphology and low cycle fatigue life variation under different laser shock process parameters are described.The results show that the distance between fatigue strips can be shortened by the laser shock peening treatment and the crack growth rate can be reduced,thus the low cycle fatigue of GH4169 life is improved.