To address this problem, researchers have tried a variety of surface treatment techniques. Among them, laser shock peening (LSP) has attracted much attention because of its excellent surface integrity. A large number of studies have shown that although laser shock peening has achieved remarkable results in improving the fatigue and friction properties of titanium alloys, the influence on fretting wear properties and related strengthening mechanisms still need in - depth exploration.
In this work, the authors systematically studied the gradient mechanical properties, surface morphology, energy dissipation, microstructure evolution and dislocation behavior of titanium alloys before and after friction tests by using a variety of microscopic techniques and energy - based analysis methods.
The research results show that the excellent fretting wear resistance of titanium alloys originates from the synergistic effect of the surface hardened layer, residual compressive stress and the evolution of the gradient nanocrystalline - amorphous sub - structure. These factors effectively inhibit the removal of the matrix material and can adapt to large plastic strains under fretting slip conditions.
Specifically, LSP enables TC6 alloy to have excellent wear - resistant properties, and the wear rate drops by 51.9% directly. During the friction process, the gradient nanocrystals promote the formation of nanocrystalline - amorphous structures, and the interaction between this structure and the work - hardened layer further improves the fretting performance.
After LSP treatment, the cross - sectional morphology of TC6 alloy shows minimal plastic deformation and no obvious defects. A hardened layer about 260μm deep and a residual compressive stress layer about 1780μm deep are formed on the surface. Compared with the untreated sample, the maximum Vickers hardness of the LSP - treated sample increases by about 12.8%, and the maximum residual compressive stress reaches 672.47MPa.
LSP induces the formation of a gradient microstructure, including a nanocrystalline layer and sub - grains at a depth of about 5μm, and a sub - structure with a high - density dislocation at a depth of about 50μm. The grain refinement of α - phase and β - phase is caused by dislocation movement, such as dislocation multiplication, entanglement, insertion, rearrangement and annihilation.
In addition, LSP slightly reduces the friction coefficient of the sample. The analysis of the friction force - displacement - load diagram, dissipated energy and surface wear morphology shows that LSP does not change the slip area or the total energy of the system, but reduces the size of spalling pits and wear debris. Smaller wear debris is helpful for forming a dense compacted layer, which can protect the matrix well.
Compared with the untreated sample, the spalling pit depth of the LSP - treated sample decreases from 10.8μm to 8.5μm, the wear rate decreases from 4.147×10⁻⁶ mm³N⁻¹m⁻¹ to 1.996×10⁻⁶ mm³N⁻¹m⁻¹, and the wear rate reduction is as high as 51.9%.
In summary, laser shock peening creates excellent wear - resistant properties of titanium alloys by inducing stable gradient nanocrystals, providing new ideas for the targeted optimization design of the surface microstructure of titanium alloys, and making important contributions to the development of aero - engines and other fields.