Mechanical Properties And Microstructure Of IN718 Nickel-base Alloy Treated By Laser Peening After High Temperature Holding

Laser Peening(LP)is an advanced surface strengthening technology that uses high strain rate dynamic shock waves generated by impact to act on the surface of the material,causing strong plastic deformation.It is capable of improving greatly the mechanical properties of the material,and its strengthening effect has excellent high temperature stability.Super-alloys are important materials in the manufacturing of aerospace turbine engines.To further enhance their high temperature mechanical properties,LP technology is used in strengthening such materials.In this paper,IN718nickel-base super-alloy was used as the research object,and the high-temperature service problem that the aerospace engine hot-end parts face encounter in their service life was studied.The internal dislocation substructure transformation and the macroscopic mechanical properties of the material were related to each other.The grain structure in the strengthening region,the evolution of dislocation configuration and the strengthening phase were also analyzed.Finally,the high temperature strengthening mechanism of LPed IN718 alloy was explored.The main research contents are as follows:(1)Based on the theory of LP and combined with the Zener-Wert-Avarmi empirical model,the residual stress relaxation mechanism induced by LP at high temperature was analyzed.According to the dislocation kinetics and the material properties of IN718 alloy,the variation of fine grain strengthening and dislocation strengthening effect induced by LP in high temperature environment was also studied.Finally,the high temperature microstructural evolution mechanism of LPed IN718 nickel based alloy was investigated.(2)High temperature holding and high temperature tensile test of IN718 alloy after LP were carried out.Based on the high temperature material properties of IN718 alloy,the residual stress relaxation behavior,microhardness change trend and high temperature tensile properties of the sample surface under different temperature environments were analyzed.The gain effect and high temperature stability of LP on the high temperature mechanical properties of IN718 alloy were systematicallyexplored.(3)Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were used to observe the grain change,dislocation characteristics and high temperature tensile fracture morphology of the LPed specimens after high temperature holding.Energy disperse spectroscopy(EDS)was used to detect the high temperature precipitation phase,and then the intrinsic relationship between the microstructure and macroscopic mechanical properties of LPed IN718 alloy held at high temperature.The results showed that LP resulted in significant dislocation proliferation and grain refinement effect;and it also provided nucleation conditions for precipitation of strengthening phase at high temperature.During the high temperature holding process,the dislocations climbed and the grain grew,the dislocation strengthening and fine grain strengthening effect were weakened.However,the increasing number of precipitation phases led to an increase in the influence of precipitation phase strengthening.And these two changes were in a competitive relationship.On this basis,the high temperature strengthening mechanism of LPed IN718 nickel based alloy was proposed.