Zhiyuan Wang

Wing skin panels and other critical aerospace load-bearing components use AA7075 aluminium alloy as their core material. They are frequently damaged by wear and erosion in service. Effective repair is therefore urgently needed. However, after conventional repair, the components often exhibit notably low strength and poor wear resistance. This problem is particularly prominent. To address this, this research introduces, for the first time, a laser surface texturing (LST) assisted cold spray hybrid process onto damaged 7075 aluminium alloy structures. The 7075-based SiC ceramic coating repaired by this process shows the following improvements: residual compressive stress increases by 17.2% and hardness by 8.7%. The bond strength increases by 48.2%. The wear rate is significantly reduced. Analysis reveals the following. The textured structure enlarges the contact area between the depositing particles and the substrate. It also guides particle deposition. This induces a more intense tamping effect, which enhances the interfacial bonding between the coating and the substrate. At the same time, the tamping effect promotes grain refinement and generates high-density lattice defects at the coating base. As a result, the strength of the coating is effectively improved. During wear, microstructural differences between the groove and sidewall regions form channels that efficiently expel wear debris. This suppresses the secondary wear caused by SiC particles. Consequently, the coefficient of friction is lowered whilst the long-term wear resistance of the coating is safeguarded. This research provides a theoretical basis and technical guidance for the high-quality damage repair and remanufacturing of critical aerospace components.

The anti-wear performance of spherical plain bearings directly affects the equipment's service life and operational reliability. Constructing a porous surface combining oil storage capacity and high hardness is an important approach to enhancing oil-lubricated wear resistance. However, bearing steel is a non-valve metal, making it difficult to achieve stable arc initiation and high-quality coating growth during conventional MAO. To address this issue, this study designed a phosphate–silicate composite electrolyte system, which enabled direct MAO on 42CrMo spherical plain bearing steel without any pretreatment, and induced hydrogen-dominated sustained deflagration behavior. The discharge characteristics, growth mechanism, microstructure, mechanical properties, and oil-lubricated tribological performance of the coating were systematically investigated.The results indicate that the direct arc initiation without pretreatment originates from an equivalent passivation layer formed synergistically by an anodic gas film and a SiO2 deposition layer. The sustained deflagration continuously inputs high-density energy into localized regions, promoting coating growth and forming a hard oil storage structure. As the sustained deflagration proceeds, the coating hardness increases from 182.12 HV to 341.37 HV, representing an enhancement of 87.44%. Meanwhile, the minimum wear rate under contact friction conditions reaches 2.71×10-4 mm3/(N·m), and further decreases to 4.28×10-5 mm3/(N·m) under oil-lubricated conditions. This study demonstrates that the hard oil storage structure can continuously store and release lubricating oil, forming a stable lubricating film at the friction interface, thereby significantly improving the wear resistance and service life of the coating. This work provides a new approach for MAO strengthening of non-valve metal spherical plain bearing surfaces.

In this study, utilising magnetron sputtering technology and by precisely controlling the structural parameters of amorphous/nanocrystalline multilayer films, we successfully fabricated a composite film system with varying modulation ratios and systematically elucidated the coupling mechanism between the film’s microstructure and tribological properties. The residual stress state of the film and the distribution characteristics of the amorphous and nanocrystalline phases have a decisive influence on its friction and wear behaviour. The amorphous phase, owing to its excellent toughness and stress buffering capacity, is capable of effectively suppressing the propagation of microcracks under alternating loads; the nanocrystalline phase, acting as a hard reinforcing phase, provides the film with superior load-bearing support through grain boundary strengthening and dispersion strengthening mechanisms; whilst the high-density, well-defined heterogeneous interfaces facilitate the effective dissipation of strain energy during friction via interfacial shear slippage and stress redistribution, thereby delaying the film failure process. Tribological performance tests indicate that the wear rate of the optimised film was significantly reduced by 28.7% and 22.1% compared to films (1#) and (3#), respectively, demonstrating excellent friction stability. By establishing a design strategy of ’stress regulation–structural optimisation–performance synergy’, this study provides a new theoretical basis and technical approach for the development of high-performance wear-resistant films.

AA7075 aluminium alloy is a critical lightweight, high-strength structural material in the aerospace sector. Its core load-bearing components are prone to wear and erosion during service. High-performance repair and strengthening technologies are therefore urgently needed. This study uses a hybrid process combining laser surface texturing (LST) with cold spraying to repair damaged AA7075 components, aiming to restore service reliability and extend component life. Compared with conventional cold-sprayed repair coatings, the coatings from this hybrid process show clear improvements. The residual compressive stress increases by 17.2%, hardness by 8.7%, bond strength by 48.2%, and the wear rate drops significantly. Experimental characterisation reveals that the laser-textured grooves increase the contact area between the deposited particles and the substrate. They also act as a guiding framework, directing particle deposition and inducing a stronger tamping effect. This promotes grain refinement and more lattice defects within the coating. As a result, strength and interfacial bonding at the coating bottom are effectively enhanced. SiC particles introduced into the coating can markedly lower the coefficient of friction (COF) during wear. However, they also cause secondary wear. Grooved coatings show clear improvement in this regard. The groove interior and sidewall differ in microstructure and properties. These differences form channels that expel abrasive particles. This suppresses secondary wear, thereby securing the long-term wear resistance of the repair layer. This study provides a theoretical basis and technical guidance for the high-quality damage repair and remanufacturing of critical aerospace components.

This study prepared a periodically structured CoCrFeNiTi/Ti-MAO film with outstanding mechanical properties. First, a multilayer CoCrFeNiTi/Ti film was deposited on the surface of 42CrMo steel, followed by micro-arc oxidation treatment. Finally, a metal/ceramic composite film with an outer ceramic hard phase and an internal high-entropy multilayer structure was successfully fabricated. The results indicate that compared with the ceramic film obtained via micro-arc oxidation on single-layer high-entropy alloy films, the average microhardness and bonding strength are increased by 40.7% and 54.9%, respectively, while the friction coefficient and service life are significantly improved. The strengthening mechanism can be summarized as follows: the valve metal film is used as a transition layer to form a multilayer structure with non-valve metal components. The transition layer is utilized to guide the micro-arc discharge, enabling the non-valve metal components to participate in the oxidation reaction. Higher voltage and temperature during the oxidation process cause phase transformation inside the ceramic film, resulting in the formation of more rutile. The surface is composed of SiO₂ formed via the reduction reaction of SiO₃²⁻ generated by electrolyte dissociation and free SiO₃²⁻ in the solution during the micro-arc oxidation process. During wear, the lubricating effect of the ground SiO₂ layer on the film surface, the inhibition effect of the high-hardness TiO₂ layer, and the strongly toughened doped layer on abrasive cutting and crack propagation, as well as the "hard shell-soft core" structure of the magnetron-sputtered amorphous/nanocrystalline layer, collectively endow the composite film with a low friction coefficient and long wear life.

In this paper, an alternating current (AC) magnetic field-assisted device was employed to enhance the preparation process of supersonic plasma spraying coatings. The phase structure and mechanical service characteristics of the five types of coatings were tested. The research found that the porosity of the coating decreased from 3.93% to 1.58%, the hardness increased from 702.88 to 921.12 HV, the bonding strength increased from 26 MPa to 38.3 MPa, and the tribological coefficient decreased from 0.6859 to 0.4670. The mechanism is that the AC magnetic field enhances the internal structure of the coating through electromagnetic stirring, electromagnetic oscillation and other effects. It also stirs the solidification process of the powder particles, improves the melting behaviour of the coating particles at the interface, and enhances the bonding quality of the coating. The improvement of the microstructure and mechanical properties further improves the tribological properties of the coating. At the same time, it is found that the higher the intensity of the AC magnetic field is not necessarily better for the improvement of the coating performance. When the AC magnetic field voltage reaches the peak of the device, the coating formation process is disturbed by the AC magnetic field, and the coating quality formed under the same spraying process is poor. Appropriate control of the AC magnetic field can effectively improve the internal structure and service quality of the coating. This provides a new technical idea and theoretical research basis for the development of advanced equipment surface engineering protection.