Study On Influence Of Temperature-Controlled Laser Shock Processing On Microstructure And Properties Of GH4169 Alloy

The most common form of failure of mechanical parts is fatigue fracture,and it is also a common failure form of aero engine blades.Modern society has high requirements on the flight performance of aircraft,which requires the aero engine to increase its thrust and thrust-to-weight ratio.Therefore,higher service requirements including fatigue life are proposed for thin-walled parts such as blades.Usually fatigue crack originated in the parts of the surface,while the surface hardening treatment technology can effectively increase the fatigue life of parts and improve the causative properties of the parts.Laser shock processing(LSP)technology is the latest and effective surface enhancement technology,which made high super strain rate plastic deformation occurs on the work piece surface,and introduced residual compressive stress(controlled size)and grain refinement layer(controllable thickness)to improve the mechanical properties of the metal material and thus suppress the initiation and development of fatigue cracks on the surface of the material.Compared with LSP,WLSP introduces a high-temperature processing condition based on LSP technology and has a better effect.There is a great significance and application value to research the performance change of materials under temperature-controlled laser shock processing.In this paper,theoretical principle of laser shock strengthening is introduced.The principle and the possible results of high temperature laser shock strengthening combined with high temperature flow stress and dynamic strain aging are analyzed and verified.GH4169 nickel-based superalloy thin-walled samples commonly used in turbofan engine blades are taken as research samples.Temperature-controlled laser shock processing technology is the research method and reasonable experiments are designed,the change before and after temperature-controlled laser shock processing of the microhardness,surface microstructure,surface topography,surface residual stress,fatigue life and the fatigue fracture morphology of samples are researched to analyze the evolution mechanism and rule of microstructure and properties.(1)High temperature laser shock strengthening combines the combined effect of shock wave mechanics and high temperature heat driving,and its strengthening effect is better than that of normal temperature laser shock strengthening.The optimum combination of the selected parameters is(5J,4 times,300?).The plastic deformation amplitude and the increasing degree of dislocation proliferation density have a positive correlation with the impact parameters.The three parameters have different effects on the strengthening effect:impact energy>impact frequency>impact temperature,in which impact energy and impact The frequency belongs to two aspects of the shock wave mechanical effect,and the temperature plays an auxiliary role in the strengthening process.(2)There appear high-density dislocation entanglement in the surface microstructure of samples after WLSP treatment.In the TEM image of the sample after WLSP treatment with parameters(5J energy,at 300?,4 shock times),it can be observed that the dislocation walls,dislocation cells and other structures caused by dislocated pile-up,tangle and climb occur around the strengthening phase of rich Nb element segregation zone.Using the white light interferometer to observe the surface topography of the shock region,it can be found that the relative depth of the pit left by the temperature-controlled laser shock processing treatment increases with shock times and the bottom morphology tends to be more flat under WLSP.The annular raised structure around the single pit by single point shock treatment can be effectively alleviated by overlap shock treatment.A special topography was observed,which was highlighted by hard points.The relative height of hard points increase with shock times,and the influence range become smaller after LSP treatment.But this local hard points are alleviated and eliminated after WLSP treatment.(3)The fatigue life of the fatigue specimens has been significantly improved after LSP treatment,in which the average high-cycle fatigue life of the specimens increases by 3.4 times with parameter(3J energy,at room temperature,4 shock times)than non-shock treatment specimens,while the high-cycle fatigue of the average fatigue specimens with parameter(6J energy,at room temperature,1 shock time)increases by 4.6 times.Through the SEM image of fatigue fracture,the fatigue core area and the crack extension zone can be seen expanded obviously.The fatigue cracks of the specimen after LSP treatment are not located on the surface of the specimen,but move toward the specimen.Under the effect of double-sided shock,fatigue final rupture region becomes smooth,a large number of dimple morphology appear in the junction area of crack extension zone and fatigue final rupture region.