超音速激光沉积硬质铝合金的疲劳性能研究OA北大核心CSTPCD

High-quality repair of damaged components during aircraft service is crucial to aircraft maintenance industry. Apart from fulfilling the dimensional requirement, restoring the fatigue properties of repaired parts has always been a challenging problem. Cold spraying is a unique coating preparation technology characterized by low-temperature solid-state deposition, and the temperature during the spraying process is much lower than the melting temperature of the original powder material, which can effectively avoid adverse effects such as oxidation, phase transition and thermal cracking caused by high-temperature coating technologies such as laser cladding and arc spraying. The deposition and formation of cold spraying coatings are based on the plastic deformation of metal powder materials under high-speed impact, and powder materials need to have good plasticity, such as copper and aluminum. However, due to the lack of ductility in hard aluminum alloy powder, the repair of structural components such as frame beams made of hard aluminum alloy suffers from insufficient coating substrate adhesion and limited coating strength, which leads to low coating density and low deposition efficiency. Supersonic laser deposition technology is a new coating preparation technology developed on the basis of cold spraying technology and laser irradiation synchronous heating technology, which can achieve effective deposition of high-strength and high hardness powder materials. It can effectively improve the interface bonding strength of the coating substrate and the strength of the coating itself. Research has shown that laser assisted heating achieves the goal of using low-cost nitrogen gas instead of helium to prepare high-quality coatings while reducing coating preparation costs and expanding the selection range of deposition materials. Supersonic laser deposition technology can improve the deposition efficiency of traditional cold spraying while retaining the characteristics of solid-state deposition in cold spraying technology. In addition, compared to laser cladding coatings, supersonic laser deposition technology has advantages such as fine structure, phase stability, less dilution and good sliding wear resistance. In the present study, the pre-notched hard Al alloy samples were repaired by cold spraying and supersonic laser deposition. The effect of different processes on the microstructure, phase composition, crystallographic characteristics of deformed grains in the coatings was studied. The fatigue properties of the repaired specimens were tested. The results showed that no phase transformation of powder material was found in the cold spraying and supersonic laser deposition coatings. Severe plastic deformation of 7075 Al alloy particles during cold spraying and supersonic laser deposition resulted in bimodal grain structure. Laser assisted heating improved the plastic deformation ability of sprayed particles and reduced the average grain size of the coating to 0.92 μm, and the localized dynamic recrystallization was responsible for such refinement. In addition, the microhardness of supersonic laser deposition layer was 196HV, which was higher than that of cold spray coating and substrate. The fatigue limit of the sample repaired by supersonic laser deposition was (135±15) MPa, which was much higher than that of the sample repaired by cold spraying. This was attributed to the enhanced cohesive and adhesive bonding strength of repaired coatings. Therefore, the study provides a novel approach for high-quality repair of damaged aircraft components.