Yuxuan Sheng

Contact fatigue, bending fatigue, and wear failures in gears are governed by the stress state, hardening gradient, microstructural stability, and surface topography within the near-surface and subsurface regions. For tooth flanks, rolling–sliding contact, asperity interaction, lubricant-film disturbance, and subsurface shear stress control micropitting, pitting, and spalling. For tooth-root fillets, local stress concentration and surface or near-surface defects dominate bending-fatigue crack initiation. Laser shock peening (LSP) introduces deep compressive residual stress, gradient hardening, and microstructural refinement, and is therefore relevant to gears when these effects are matched to the critical damage zones. This review examines LSP of gear steels and related load-bearing steels from the viewpoint of tooth-flank and tooth-root damage control. It links laser parameters, shock-induced plastic deformation, residual-stress depth, hardening response, surface roughness, and profile accuracy to bending fatigue, rolling contact fatigue, and wear behavior. LSP is most effective when the compressive residual-stress layer and hardened layer reach the contact- or bending-damage depth while lubrication compatibility, flank form accuracy, and subsequent finishing are preserved. Excessive pulse energy, overlap, or unstable absorbing/confining conditions may increase roughness, produce ablation or micropitting-sensitive defects, and compromise tooth profile accuracy. Thus, LSP for gears should be evaluated together with carburizing, nitriding, shot peening, surface rolling, polishing, coatings, and laser texturing rather than as an isolated treatment. The central task is to define gear-specific process windows that balance residual-stress depth, surface integrity, dimensional accuracy, and manufacturing repeatability.

High-performance electrode materials are fundamental to improving supercapacitor performance, serving as key factors in developing devices with high energy density, high power density, and excellent cyclic stability. Non-stoichiometric spinels with phase deficiencies can achieve electrochemical performance that surpasses that of stoichiometric materials, owing to their unique structural characteristics. In this study, we used a microwave-assisted method to synthesize a high-performance non-stoichiometric spinel material with phase deficiencies, Mn_0.5Co_2.5O₄, which displayed a wide potential window (1.13 V in a traditional aqueous three-electrode system) and high specific capacitance (716.9 F g⁻¹ at 1 A g⁻¹). More critically, through microwave-assisted doping engineering, nickel was successfully doped into the phase-deficient Mn_0.5Co_2.5O₄, resulting in a spinel material, Ni−Mn_0.5Co_2.5O₄, with significant lattice defects and a mixed 1D/2D morphology. The doping of nickel effectively promoted the high-state conversion of manganese valence states within the manganese cobaltite material, substantially increasing the quantity of highly active Co³⁺ ions. These changes led to an increase in the density of reactive sites, effectively promoting synergistic interactions, thereby significantly enhancing the material’s conductivity and energy storage performance. The specific capacitance of Ni−Mn_0.5Co_2.5O₄ reached 1180.6 F g⁻¹ at 1 A g⁻¹, a 64.7% improvement over the original Mn_0.5Co_2.5O₄; at a high current density of 10 A g⁻¹, the capacitance increased by 14.3%. Notably, the charge transfer resistance was reduced by a factor of 41.6. After 5000 cycles of testing, the capacity retention stood at 79.2%. This work reveals the effectiveness of microwave-assisted doping engineering in constructing high-performance non-stoichiometric spinel-type bimetallic oxide materials, offering advanced strategies for the development of high-performance electrode materials.