无涂层激光冲击强化工艺参数对 AISI 9310 齿轮钢 力学性能与表面完整性的影响

Gears constitute the core components of helicopter reducers, and the failure of heavy-load transmission gears directly impacts the reliable operation of the reducer, potentially endangering the service safety of the helicopter. Enhancing the service performance and reliable working margin of gears through surface post-treatment technologies holds significant military and economic value. Laser shock peening, as an advanced surface strengthening technique, aims to achieve efficient surface modification of metallic materials. However, its application to geometrically complex parts presents technical challenges. Therefore, an attempt is made to modify the surface of gears using laser shock peening without coatings. To verify the efficacy of laser shock peening without coatings in improving the properties of gear steel, strengthening experiments are conducted with varying process parameters. The experiment innovatively employs a smaller spot size and lower energy level for processing. Specimens of specific material grades undergo grinding, vacuum carburizing, and heat treatment to simulate the transmission gears of a reducer, providing a process reference for real gear components. AISI 9310 steel, a typical martensitic steel, is selected for study. The sample exhibits a complete carburized layer of approximately 420 μm, with a stable hardness of 625 HV within this range. Beyond 1 000 μm, where the matrix is entirely outside the carburizing zone, the hardness stabilizes at 430 HV. The laser beam interacts directly with the specimen in an atmospheric environment. Given the unique structure of gear parts, a water-optical coaxial strengthening method is adopted. During the optimization of the laser process, laser energy is first optimized, followed by the number of laser shocks. The effects of laser parameters on mechanical properties and surface morphology are systematically analyzed. The samples are characterized using an optical microscope, microhardness tester, residual stress meter, roughness meter, and atomic force microscope. The results indicate that laser shock peening without coatings introduces a maximum work-hardened layer of 530 μm and a residual compressive stress layer of 450 μm in the depth direction of the sample. The substantial improvement in subsurface mechanical properties is attributed to the plastic deformation induced by the plasma shock wave in the gradient direction. After strengthening, the maximum hardness reaches 689.9 HV, and the residual compressive stress increases to 738.9 MPa. The direct irradiation of the laser beam on the sample surface leads to heat accumulation, causing a rapid increase in surface roughness to a maximum of 1.509 μm. This results in the formation of a periodic micro-convex structure with a regular arrangement. As laser energy and the number of shocks increase, this structure gradually evolves into a regular rectangular pattern, exhibiting self-lubrication properties. An effective work-hardening layer is formed along the depth direction of the specimen after strengthening. An increase in laser energy or frequency significantly enhances the work-hardening effect of laser shock peening without coatings. Additionally, a high-amplitude residual compressive stress is introduced into the specimen along the depth direction, forming a residual compressive stress layer with the same thickness as the hardened layer. The results of process optimization reveal that a surface treated with 120 mJ per strengthening cycle, applied twice, forms a periodic rectangular microstructure pattern, resulting in the most significant improvement in comprehensive mechanical properties. The influence of laser shock peening without coatings process parameters on the properties of AISI 9310 steel is studied, and the process parameters are further optimized. The effectiveness of laser shock peening without coatings in improving the mechanical properties of gear steel materials is verified, providing data accumulation and technical support for the subsequent enhancement of friction performance, rolling contact fatigue performance, and bending fatigue performance of gears.