Tool coatings involve the application of special materials on the tool surface to effectively extend tool life and improve processing efficiency. Currently, TiAlN coating is one of the most widely used coatings in high-speed cutting and dry cutting. However, traditional TiAlN-coated tools have a relatively high friction coefficient in dry cutting, causing elevated temperatures between the friction surfaces, ultimately leading to severe coating wear. Moreover, as the demand for high-performance coatings in cutting technology increases, simple single-layer coatings are no longer sufficient to meet cutting requirements. Multi-functional coating structures, such as gradient coatings and soft/hard composite coatings, are increasingly being utilized. Additionally, DLC coatings (diamond-like carbon), especially a-C(hydrogen-containing diamond-like carbon) coatings, have high hardness and excellent lubricity, making them suitable as solid lubricant coatings. Therefore, if the outstanding self-lubrication and corrosion resistance properties of DLC coatings and the oxidation resistance and high hardness advantages of TiAlN coatings can be combined on the tool surface to form a DLC/TiAlN composite coating, the overall performance and service life of the tool can be further improved. However, DLC coatings have an interface adhesion problem, and their high mechanical stress and elevated friction temperature often cause cracks to initiate and coating peeling at the interface, leading to premature failure of the DLC coating. Additionally, it is challenging to coat non-crystalline DLC onto crystalline TiAlN. Therefore, solving the interface bonding issue is the key factor affecting the service life of the DLC/TiAlN composite coating.
Studies have shown that surface microtexturing technology can enhance the surface performance of coated cutting tools. In the field of surface texturing research, various surface processing methods have attracted the attention of researchers, such as fine micro-milling, photolithography, electrochemical machining, and laser processing. Among these methods, laser processing technology has gained popularity among researchers due to its advantages of no pollution and high efficiency.The DLC coating was deposited on the surface of untreated TiAlN coating samples and textured TiAlN coating samples using magnetron sputtering technology to prepare DLC/TiAlN composite coatings. The effects of different laser scanning speeds (1000 mm/s, 1500 mm/s, and 2 000 mm/s) on the coating properties were studied under air and liquid processing media. The macro/micro mechanical properties, friction, and wear properties of all laser-treated single-layer TiAlN coatings and DLC/TiAlN composite coatings were systematically characterized. The results show that at a laser scanning speed of 2 000 mm/s, the hardness and film-substrate bonding strength of the liquid-assisted laser-treated TiAlN coating and DLC/TiAlN composite coatings are the largest, and the wear loss and average friction coefficient are the smallest. Liquid-phase assisted laser treatment can not only reduce the residual internal stress in DLC coating, but also present fewer defects and good adhesion properties on the surface of TiAlN coating samples, which provides better support effect for the deposition of DLC coating, and then enhances the bonding strength and friction and wear properties of DLC/TiAlN composite coatings.
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