Research On Mechanical Property And Hot Corrosion Behavior Of TC11 Titanium Alloy By Laser Shock Peening

High temperature alloys are important structural materials for high performance manufacturing industry.Titanium alloy is used for making blades,compressor disk,turbine disk of the aircraft engine.In actual working environment,the key components like the leaves are prone to fatigue crack,fatigue fracture and surface corrosion.Therefore,it is necessary to improve its mechanical properties and corrosion resistance.Laser shock peening(LSP)is a new surface strengthening technology,which can effectively improve the mechanical properties of the material and enhance its corrosion resistance.In this paper,hot corrosion and performance test experiment have been conducted on TC11 titanium alloy before and after LSP.The results show that LSP can improve the mechanical properties and the corrosion resistance performance of TC11 titanium alloy.The strengthening mechanisms and corrosion resistance enhanced mechanisms are also analyzed.The research contents and conclusions are as follows:Firstly,the energy conversion and impact process of laser shock wave from the protective layer,the constraint layer and the metal surface are analyzed.Through the theoretical analysis and deduction,the experimental parameters of laser shock TC11 titanium alloy have been optimized.Secondly,the mechanical properties of TC11 titanium alloy,such as surface residual stress,surface roughness,three-dimensional morphology and micro-hardness were investigated.Based on the temporary theory,the mechanism of laser shock strengthening to improve the mechanical properties of materials is explained.The results show that,after laser shock,the maximum residual compressive stress is on the surface,the depth of the stress layer increases with the impact times grow;The hardness increased weakly,when the impact number increased to a certain extent;Thirdly,the process of dislocation movement and grain refinement of TC11 titanium alloy after laser shock peening was studied.The results show that as the plastic deformation occurs on the surface,the unevenly distributed dislocations will propagate.The dislocation,the dislocation cell and the twin will be formed due to the interaction among the dislocations.The dislocation motion continues to develop,and the sub-grain boundaries are formed.The new structure will cut the original grain structure,so that the grain is refined gradually.The grain refinement will be completed,until the internal energy is stable.Fourthly,the feasibility of laser shock strengthening to strengthen the corrosion resistance of TC11 titanium alloy was proved.The experimental results show that after laser shock,the incubation period of hot corrosion of titanium alloy TC11 extended,the corrosion rate increases;The oxide layer and corrosion layer formed in the hot corrosion process;After laser shock,surface oxidation layer is more tightly integrated,the cracks,pits and spalling was suppressed on the corrosion of the surface;With the increase of temperature and time,the corrosion intensifies,surface corrosion pits and cracks,spalling phenomenon has intensified.Finally,the corrosion morphology and corrosion resistance of TC11 titanium alloy were investigated.The results show that the hot corrosion is the process from the formation of oxide film to crack,pit,and then to the spalling of oxide film.After laser shock,the produced residual compressive stress can reduce cracks,increase the adhesion of oxide and substrate surface,reduce stress corrosion and prevent corrosion aggravating;Dislocation movement in alloy will cut the original grain and lead crystal grain refinement.The internal defects and grain refinement produced by dislocation movement can improve the mechanical properties of the alloy,improve the stability of the surface structure,make the oxide become compact and uniform,then it can enhance the plasticity of alloys and improve its corrosion resistance.