| TC17 titanium alloy is called "three high titanium alloy" because of its high strength,high toughness and high hardenability.It is widely used in the manufacture of aero-engine compressor blades and blisks.However,its poor fatigue resistance limits its application and development in the aerospace field.Shot peening technology can effectively improve the fatigue properties of materials,so it is widely used in the aerospace field.In this paper,laser confocal microscope,scanning electron microscope,X-ray diffractometer,Vickers hardness tester and spin-bending fatigue tester are used to systematically study the surface integrity and fatigue performance of TC17 titanium alloy sheet and blades after dry and wet shot peening.After TC17 titanium alloy is treated with different strength of dry and wet shot peening,the surface roughness will increase with the increase of shot peening strength.The surface roughness after dry shot peening is 0.576～1.296 μm,and that after wet shot peening is0.244～0.485 μm.After dry and wet shot peening,the surface layer of the target has a significant work hardening effect,which increases the hardness of the surface layer significantly.As the depth increases from the surface to the inside,the hardness gradually decreases,eventually approaching the matrix hardness(～390 HV).After dry shot peening,the surface hardness is540～590 HV,and the depth of the hardened layer is 130～150 μm;after wet shot peening,the surface hardness is 494.8～507 HV,and the depth of the hardened layer is 100～120 μm.In addition,the surface layer of the target produces residual stress fields with different thicknesses.Except when the wet shot peening strength is 0.21 mm N,the maximum residual stress is on the surface,and the other maximum residual stresses are all on the subsurface.The residual stress field presents a typical "check" curve.After dry shot peening,the residual stress field depth of TC17 titanium alloy is 200～250 μm,and the maximum residual stress can reach-1191.5 MPa;after wet shot peening,the depth of the residual stress field is 80～190 μm,and the maximum residual stress can reach-943.9 MPa.When the shot peening strength increases from 0.40 mm N to 0.50 mm N,the phenomenon of "over shot peening" appeares in both dry and wet shot peening near the surface.The hardness of the near-surface layer decreases and the residual stress relaxes.After EBSD analysis,it is found that the phenomenon of “over shot peening” is caused by excessively high-strength shot peening,which causes a large number of small-angle grain boundaries to absorb dislocations and convert them into large-angle grain boundaries,which makes the intragranular dislocation density decrease and softening effect,which leads to stress relaxation.The results of the rotating bending fatigue test show that both dry and wet shot peening can improve the fatigue life and fatigue limit of TC17 titanium alloy to different degrees.Dry and wet shot peening can increase the fatigue life of TC17 titanium alloy by 12-40 times and14-45 times,respectively.When the shot peening strength is 0.30 mm N and 0.50 mm N,the fatigue life of titanium alloy has the most significant improvement effect.After dry and wet shot peening,the fatigue life of TC17 titanium alloy can be increased by 12～40 times and 14～45times,respectively.When the shot peening strength is 0.30 mm N and 0.50 mm N,the fatigue life improvement effect of titanium alloy is the most significant.By analyzing the fatigue fracture of the TC17 titanium alloy,it is found that the source of the cracks in the unshot-peened fatigue specimen is located on the surface of the specimen.After dry shot peening,when the shot peening strength is between 0.21 and 0.30 mm N,the crack sources are all located in the subsurface layer.When the shot peening strength is between 0.40 and 0.50 mm N,most of the crack sources originate on the surface,and a few originate on the subsurface layer;after wet shot peening,the crack sources are all located on the subsurface layer. |
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