| The most critical component of aircraft is the engine,while domestic aeroengine manufacturing technology is relatively backward and can not be obtained from abroad.In order to ensure the safety of national airspace,the research and development of aeroengine key technology is very important and urgent.Nickel-base powder superalloy FGH95 can be used to manufacture the key part of domestic aeroengine-turbine disk.Due to the harsh service environment and the action of blade tenon,the mortise of turbine disk is prone to fatigue microcracks and fracture.Fatigue has become an urgent technical problem to be solved in turbine disk mortise.Traditional shot peening has some problems,such as shallow compressive residual stress layer,surface micro damage,missed spray and so on,which can not effectively solve the fatigue problem.LSP is an excellent surface strengthening technology and an effective method to effectively solve this technical problem.The published literature only reports the LSP research of american GE company on the blade tenon of large engine,and there is no LSP research on the turbine disk mortise of small engine(helicopter engine)with complex and narrow spatial structure.Supported by the X project of AECC Hunan Aviation Powerplant Research Institute,this thesis was carried out LSP research on the complex structure of key parts of new helicopter engine,and the following research results were obtained:(1)For the first time,the mortise structure of a domestic helicopter engine turbine disk was studied,and the accessibility of laser beam to the narrow mortise structure was determined by the robot offline programming software of LSP system.The effects of LSP treatment of incidence angle,laser energy and shock times on the surface integrity(surface morphology,surface roughness,residual stress and microhardness)of FGH95 alloy used for turbine disk material were studied,which provided guidance for the selection of process parameters of oblique incident LSP treatment.The maximum residual compressive stress reached-529.6MPa.(2)Based on the above research,aiming at the phenomenon that the residual stress induced by LSP will relax and redistribute under various loads,the effects of temperature(mplitude and time),cyclic load(cycles,value and load ratio),and the dual treatment of temperature and cyclic load on the residual stress relaxation of FGH95 powder alloy after LSP treatment were studied,and the analysis model of relevant residual stress relaxation was constructed.The purpose is to understand the strengthening effect and stability of the alloy under thermal load and cyclic load after LSP treatment.(3)In view of the problem that tensile fatigue cracking is easy to occur at the mortise root of the turbine disk,the effects of shock times of LSP and temperature on the tensile fatigue properties were studied.The tensile fatigue life of LSP treated samples at room temperature could be increased by 108.8%;Even at high temperature,the tensile fatigue life could be increased by up to 68.6%.The strengthening mechanism was revealed by fracture morphology analysis.The residual compressive stress and microstructure induced by LSP can inhibit crack initiation and transfer the fatigue source zone,reduce the fatigue crack growth rate and fatigue striations spacing,and increase the plastic deformation in the final fracture zone.(4)Due to the high-frequency vibration contact of blade tenon,the contact surface of the mortise surface of the turbine disk is prone to fretting wear and fatigue fracture.The effects of shock times of LSP and temperature on the fretting fatigue properties were studied.The fretting fatigue life of LSP treated samples at room temperature could be increased by 103.0%;At high temperature,the fretting fatigue life could be increased by68.5%.Through the analysis of fracture morphology,the fracture developing zone of fretting fatigue and tensile fatigue samples were compared.It is revealed that the wear in transverse of contact pads would promote the initiation of fatigue cracks;Due to the compressive force of the transverse contact pads,the degree of plastic deformation of the fretting specimens would increase,the dimension of dimple changed obviously,the quasi-cleavage facets appeared,and the tear ridge characteristics increased obviously.The fretting fatigue life was less than the tensile fatigue life.(5)The residual stress of simulation and experiment were analyzed by the least square method,the flat-topped order of laser beam was corrected,and the pressure distribution model that better matches the shock wave induced by the flat-top laser beam was constructed;Due to the thin thickness and poor stiffness of the turbine disk mortise,the residual stress of the turbine disk mortise was compared between the LSP finite element simulation and the experiment by using the treatment method of equal laser power density and variable pulse width.The results show that the results of turbine disk mortise experiment were close to those of finite element simulation.The treatment method of equal power density and small pulse width can ensure the effect of strengthening the surface and reduce strain of turbine disk mortise. |
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