激光冲击强化前处理对TiN/Ti涂层/基体疲劳性能的影响

The anti-erosion TiN/Ti coating with multilayer gradient structure was prepared on the surface of TC4 titanium alloy by filtered cathodic vacuum arc (FCVA) deposition method. The substrate is subjected to laser shock strengthening pretreatment before deposition. The surface morphologies and mechanical properties of the specimens were characterized by atomic force microscope, nanoindentation, and scratch tester. The fatigue properties of the specimens were evaluated and the fatigue fracture morphologies were analyzed. The results showed that the LSP pretreatment formed a hardened layer with a thickness of about 300 μm, high hardness, and residual compressive stress on the surface of TC4. The average fatigue strength of the TC4 alloy is 373.8 MPa, and the fatigue strength of the sample after preparing the TiN/Ti coating is 363.7 MPa, which is slightly lower than that of the original substrate. The fatigue strength of the sample after LSP-pretreatment is 411.9 MPa, which is 13.3% higher than that of the TiN/Ti coated sample and 10.2% higher than that of the uncoated sample. TiN/Ti coating can inhibit the initiation of cracks on the surface and slow down its growth rate. However, the crack suppression effect is limited when the TiN/Ti coating is broken and peels off from the substrate during the tensile process, and the break of the coating promotes the crack propagation. After LSP pretreatment, the hardened layer formed on the surface of TC4 furtherincreases the difficulty of crack initiation, and the increased bonding strength can reduce the crack growth rate.