Yongyong He

Fine Particle Peening (FPP) is a new surface-treatment method developed in the 21st century, which derived from Custom Shot Peening (CSP). This research aims to investigate the FPP process for 18Cr2Ni4WA gear steel, to find a parameter optimization scheme, and to analyse the characteristics of FPP reinforcement in theory. A series of analyses including surface morphology, roughness, microhardness, residual stress distribution and cross-section crystalline phase, grain boundary, element component, and texture were used to clarify the effects of process parameters like shot peening pressure, shot peening flow rate, and shot peening coverage on the effectiveness of FPP reinforcement. The results show that increasing the shot peening pressure can result in higher surface hardness and residual stress, but excessively high surface hardness may cause surface cracking. Increasing the shot peening coverage can improve surface isotropy and produce a deeper layer of grain refinement. This work employs theories like micro-plough effort to explain the effort of FPP parameters. Considering the actual operating conditions of the shot peening instrument, this article selects flow rate of 30, pressure of 3 bar, and coverage of 200% as the process optimization scheme. The finding of this research has a guiding significance for optimization of the actual heavy-loaded gear surface strengthen processing progress.

Hardening gradients have been introduced to heavy-duty gears in order to enhance their bearing capacity, but this has led to an increase in the complexity and difficulty of fatigue analysis. To explore ways to mitigate this, in this paper a contact fatigue model of an 18CrNiMo7-6 gear pair with a hardness gradient was established, and the Brown-Miller-Morrow multiaxial fatigue criterion was adopted to calculate the contact fatigue lifespan under different contact pressures. The gear contact fatigue limit was then determined by fitting the S-N curve. The accuracy of this gear contact fatigue limit prediction method was validated experimentally. Furthermore, the effects of case hardening depth (CHD) and surface hardness (SH) on contact fatigue lifespan and limits were explored, and we found that the contact fatigue limit of the typical carburized gear was more affected by SH than CHD. In addition, we also examined which hardness gradients were more beneficial for the fatigue performance of gears with atypical hardening gradients.

Owing to the great barrier properties, light weight and environmental friendliness, graphene-based anticorrosion coatings are considered to be promising candidates for next-generation anticorrosion materials. Recently, polydopamine has showed considerable research value and application prospects in the field of anticorrosion, and provided new opportunities for chemical modification of graphene for the enhancement of coating performance. However, the applications and mechanisms of polydopamine-modified graphene in anticorrosion coatings have not been systematically summarized. This review focuses on the application and mechanism of graphene and polydopamine-modified graphene in anticorrosion coatings. Firstly, the intrinsic barrier properties and applications of graphene in anticorrosion coatings are summarized, especially in self-healing anticorrosion coatings. Next, the properties and applications of polydopamine in the field of anticorrosion are reviewed and discussed. Moreover, the application and mechanism of polydopamine in graphene-based anticorrosion coatings are systematically reviewed, which mainly includes enhancing the intrinsic barrier properties, improving the dispersibility, modifying with functional materials, and introducing pH-responsive properties. Finally, the critical challenges and future prospects for the development of graphene-based anticorrosion coatings are discussed. This article aims to boost further development of graphene-based anticorrosion coatings to solve the anticorrosion bottleneck of equipment in harsh corrosive environments.

Under extreme conditions such as high speed and heavy load, 18Cr2Ni4WA steel cannot meet the service requirements even after carburizing and quenching processes. In order to obtain better surface mechanical properties and tribological property, a hollow cathode ion source diffusion strengthening device was used to nitride the traditional carburizing and quenching samples. Unlike traditional ion carbonitriding technology, the low-temperature ion carbonitriding technology used in this article can increase the surface hardness of the material by 50% after 3 h of treatment, from the original 600 HV_0.1 to 900 HV_0.1, while the core hardness only decreases by less than 20%. The effect of post-ion carbonitriding treatment on mechanical properties and tribological properties of the carburized and quenched 18Cr2Ni4WA steel was investigated. Samples in different treatment are characterized using optical microscopy (OM), scanning electron microscopy (SEM), optimal SRV-4 high temperature tribotester, as well as Vickers hardness tester. Under two conditions of 6N light load and 60 N heavy load, compared with untreated samples, the wear rate of ion carbonitriding samples decreased by more than 99%, while the friction coefficient remained basically unchanged. Furthermore, the careful selection of ion nitrocarburizing and carburizing tempering temperatures in this study has been shown to significantly enhance surface hardness and wear resistance, while preserving the overall hardness of the carburized sample. The present study demonstrates the potential of ion carbonitriding technology as a viable post-treatment method for carburized gears.