Enhancement in fatigue property of Ti-6Al-4V alloy remanufactured by combined laser cladding and laser shock peening processes

Abstract

To improve the fatigue performance of remanufactured Ti-6Al-4V alloy, the combined laser cladding and laser shock peening(LSP) processes, as an anti-fatigue remanufacturing method, was adopted to restore the geometric shape of the simulated damaged samples and modify surface integrities of the repaired region. Microstructure variation, residual stress distribution, fatigue crack propogation rate and fracture morphology of Ti-6Al-4V alloy samples were examined before and after anti-fatigue remanufacturing. The results indicated that the laser cladding repaired component evolved gradually from equiaxed α and a small amount of β in the repaired substrate to typical Widmanstätten structure with fine acicular α and α + β basket weave in the repaired region. In anti-fatigue remanufactured zone, no new crystalline phase was created, β and α phases were refined obviously, high-density dislocations and abundant nanotwins with thickness of 10 to 30 nm were generated, and residual tensile stress was converted into compressive stress with the affected depth of about 900 μm. After anti-fatigue remanufacturing, the mean fatigue life of Ti-6Al-4V alloy samples was 2.64 times that of the matrix samples. A new method for calculating crack growth rate considering experimental uncertainty was presented. The fatigue crack propagation rate of Ti-6Al-4V specimens after anti-fatigue remanufacturing was significantly smaller than that of substrate samples, which was primarily attributed to the combined effects of Widmanstätten structure produced by laser cladding and LSP-induced favourable microstructural modification and the removing of tensile residual stress in the laser-clad repaired region.