Bicheng Guo

This study focuses on H13 steel and addresses the discontinuous surface strengthening response in conventional rectangular-overlap laser shock peening caused by the dispersed coverage number distribution, where regions with coverage numbers of 2-4 coexist. A close-packed laser spot overlapping strategy was proposed to optimize the coverage number distribution. Coverage number statistics and coefficient of variation analysis showed that the treated area was regulated into a low-dispersion state, with the coverage number difference controlled within 1. The effects of strengthening uniformity on surface integrity, wear resistance, and fatigue performance were evaluated using the coefficients of variation of morphology, hardness, and residual stress. Coverage number distribution affects the accumulation and spatial continuity of surface plastic deformation. A large coverage number difference causes insufficient deformation in low-coverage regions and excessive plastic flow in locally high-coverage regions, causing fluctuations in surface topography, hardness, and residual compressive stress fields. In contrast, a low-dispersion coverage number distribution promotes continuous plastic strain accumulation between spots and forms more uniform grain-refined, work-hardened, and residual compressive stress layers. the third close-packed laser spot overlapping strategy (HCP-3) exhibited the best performance: surface roughness (Sa) was reduced to 0.550 μm, average grain size to 2.05 μm, surface hardness and residual compressive stress reached 708.67 HV and -897.69 MPa, wear volume was reduced to 0.492 mm³, and fatigue life increased to 1.80 × 106 cycles. These results demonstrate that optimizing coverage number distribution improves the surface integrity and fatigue performance of laser shock peened H13 steel.

This study systematically investigates the dynamic mechanical behavior and constitutive modeling of low-temperature quenched and tempered 42CrMo steel under high-strain-rate and high-temperature conditions. Dynamic compression tests were performed using a split Hopkinson pressure bar (SHPB) system over a strain rate range of 460–6450 s⁻¹ and a temperature range of 25–800 °C. The results show that the flow stress of quenched 42CrMo steel exhibits significant strain hardening and temperature softening effects, while its strain rate sensitivity is observed to be relatively low, especially under ultra-high-strain-rate conditions. Based on the experimental data, both the Power-Law and Johnson–Cook constitutive models were established. A hardness-based temperature softening coefficient was introduced to convert the experimental stress–strain curves into isothermal stress–strain curves, thereby effectively decoupling the coupled effects of strain rate and temperature. Error analysis indicates that the Power-Law model yields an average fitting error of 1.98%, which is superior to that of the Johnson–Cook model (3.23%), suggesting that the Power-Law model is more suitable for describing the dynamic mechanical behavior of low-temperature quenched and tempered 42CrMo steel. The findings of this study provide a reliable constitutive basis for numerical simulations of low-temperature quenched and tempered 42CrMo steel under extreme thermomechanical coupling conditions, such as high-speed cutting and impact forming.

In steam turbines, blades operate in a high-speed wet steam environment and are often damaged by combined erosion from liquid droplets and solid particles. To reveal the mechanism of composite modification via high velocity oxy-fuel spraying (HVOF) and laser shock peening (LSP) on improving blade erosion resistance, an accelerated erosion experimental method was designed in this work. Five different processes were proposed, including UT, LSP, UT-HVOF, LSP-HVOF, and HVOF-LSP. The results indicate that compared with UT specimens, LSP treatment induces high compressive residual stress in the surface layer of 1Cr12Ni3Mo2VN stainless steel, which leads to shallower compound erosion pits. Compared with UT-HVOF and LSP-HVOF specimens, the HVOF-LSP specimen has the lowest coating porosity and the highest surface microhardness of 1500 HV0.5, representing an increase of 14.5% and 8.7% respectively. This demonstrates that LSP post-treatment can enhance the load-bearing capacity of HVOF coatings effectively. Microstructural analysis further reveals that the HVOF-LSP specimen presents the shallowest erosion pits and the longest penetration lifetime of the WC coating. Accordingly, the HVOF-LSP treatment can effectively improve the service life and protection performance of materials under accelerated erosion conditions, providing a technical reference for the long-term service of turbine blades.

To address the bottleneck issues of traditional ultrasonic polishing—such as unclear material removal mechanisms for ductile metals and difficulties in controlling machining outcomes—this paper employs a combined approach of computational fluid dynamics (CFD) simulation and non-contact fixed-point polishing experiments to systematically reveal the intrinsic relationship between the dynamic characteristics of the polishing flow field and the evolution of the material surface. Numerical simulations demonstrate that the cavitation effect significantly regulates the flow field structure: it not only confines the minimum pressure near the saturated vapor pressure but also markedly reduces the pressure peak while concurrently causing an overall decrease in flow velocity, forming a strongly coupled multi-parameter system of pressure, cavitation, and flow velocity. Experimental results indicate a clear spatial differentiation in the material removal mechanism: the central region is dominated by cavitation erosion, resulting in numerous pits and a 33.6% increase in residual compressive stress; the edge region is primarily governed by fluid-mechanical scraping, effectively improving surface finish and increasing residual stress by 22.3%; the transition zone, influenced by synergistic mechanisms, shows the smallest stress increase (19.7%). The enhancement of residual compressive stress can significantly improve the fatigue resistance of materials and prolong their fatigue life. This study comprehensively elucidates the multi-mechanism synergistic material removal process involving “cavitation impact, mechanical scraping, and fatigue spallation” in ultrasonic polishing, providing a key theoretical basis and process optimization direction for sub-micrometer ultra-precision machining.

To improve the fatigue life of high-strength bolts, this study builds upon conventional thread rolling by introducing a localized rolling reinforcement process specifically at the thread root. Experimental specimens were prepared from 42CrMo high-strength bolts using a combined manufacturing technique that integrates thread forming and root rolling. A comparative analysis was conducted to evaluate the fatigue performance of bolts with and without the root rolling reinforcement. The experimental results demonstrated that the thread root rolling treatment further refines the surface grains beyond the effects of standard thread rolling. At a rolling force of 2.5 kN, the surface microhardness increased from the original 500 HV0.2 to 540 HV0.2. The process also improved surface finish, reduced grain size, and increased dislocation density. The optimal enhancement was achieved at a rolling force of 3.5 kN, resulting in an approximately 11-fold improvement in fatigue life. Fractographic analysis via Scanning Electron Microscopy (SEM) indicated a reduced number of crack initiation sites. This study confirms the effectiveness of the proposed rolling reinforcement process, offering a viable technical pathway for optimizing the anti-fatigue manufacturing of high-strength bolts.

The internal surfaces of hot-working dies are prone to wear and fatigue fracture during service, often necessitating surface modification and strengthening. Among available techniques, laser shock peening (LSP) is an effective surface strengthening method. However, when treating internal surfaces, achieving perpendicular laser incidence is difficult, and irradiation must often be applied at an angle. To clarify the relationship between the laser incidence angle and the strengthening effect, this study applied laser shock peening to H13 steel at various incidence angles(0°, 15°, 30°, 45°) with a spot diameter of 3 mm, using laser energies of 8 J, 8.2 J, 9.2 J, and 11.3 J, respectively, and maintaining a fixed power density of 1.41 GW/cm². By maintaining a consistent power density through laser energy compensation, the influence of the incidence angle on surface integrity and wear resistance of the hole structure was systematically investigated. The results show that as the impact angle increases from 0° to 45°, the depth of the affected material layer gradually decreases. Surface microhardness and residual compressive stress peak at a 30° impact angle, reaching values of 633.5 HV1 and 517.4 Mpa, respectively. Wear tests indicated that the friction coefficient was lowest at 30° (0.542), with the dominant wear mechanism shifting from abrasive to adhesive wear. Under controlled power density conditions, oblique laser impact improves surface properties at the expense of a reduced thickness of the affected layer.

In the service process of gears, premature fatigue failure or fracture of gears is often caused by poor surface performance. 20CrNiMo steel is a commonly used material for gears. Laser-shock peening (LSP), carburizing treatment (CT), and hybrid modification of carburizing treatment and laser-shock peening (LSP + CT) were carried out to improve the performance of 20CrNiMo steel. The hardness, residual stress, microstructure, subgrain size, and toughness of the samples were analyzed following various modification methods. It was observed that the properties of the composite-modified gradient structure materials achieved through carburizing and laser-shock peening were superior to those modified using single methods. After the composite treatment of carburizing and laser shocking, the samples exhibited the most significant increase in hardness, up to 916HV0.1, with a surface layer experiencing residual compressive stress as low as −635 MPa. Simultaneously, a gradient microstructure was formed on the surface layer, with 80% of the crystallites being in the nanoscale range. Furthermore, the toughness was notably enhanced. Experimental results confirm the improvement in the properties of 20CrNiMo samples, resulting in the creation of a functionally graded material through the composite treatment of carburizing and laser shocking.