Research Status and Progress of Improving Mechanical Properties of TiAlSiN Coatings

TiAlSiN coatings have excellent high temperature resistance and chemical inertness, and they have been widely used on friction work pieces and cutting tools. However, their high internal stress limits their further application in industries under harshworking conditions. This paper focuses on the main techniques employed to improve the mechanical properties of TiAlSiN coatings, including microstructure optimization, micro-structure design and treatment. The coating hardness is predominantly influenced by microstructure, which can be tailored through various processing methods such as deposition method optimization, and modulation of the deposition process parameters including nitrogen flow rate, substrate bias, target quantity, and power duration. In addition, doping new elements and changing the original element content of TiAlSiN coatings also affect the hardness of the coatings. In this work, the mechanisms involved in improving the mechanical properties of the coatings, such as fine grain strengthening, solid solution strengthening and modulus difference theory, were compared and analyzed. The refinement of grain size resulting from fine-crystal strengthening reduced the crack propagation, while solid-solution strengthening was achieved by introducing foreign atoms into a compound to form a solid solution, thereby increasing the hardness of the TiAlSiN coatings. The coherent effect and modulus difference theory promoted the enhancement of TiAlSiN coating hardness through interface structure optimization. Both mechanisms induced interfacial stresses that prevented dislocation generation. The internal relations and differences between the above theories were compared and analyzed in detail. The effect of nano-multilayer and gradient composite layers on the mechanical properties of the coatings was systematically discussed. Modulation structure and composition adjustment were the two main factors that affected the variation of micro-structure. Currently, research on the strengthening mechanisms of nano-layered coatings and gradient-structured coatings is not comprehensive. Even small structural alterations to these coatings can cause various influence mechanisms that alter their mechanical properties. For instance, changing the modulation period significantly impacts the mechanical behavior of TiAlSiN coatings by means of coherent strain and the modulus difference theory. It is helpful to guide the design of membrane structure with good mechanical properties. In addition, heat treatment has the most significant effect on the properties of TiAlSiN coatings. So the influence of annealing temperature, annealing time, and atmosphere on the mechanical properties of TiAlSiN coatings was summarized. The effect of annealing conditions on the microstructure of the coatings and the relationship between the microstructure and mechanical properties were analyzed. In addition to experimental research, basic theoretical research was also be conducted by starting from first principles to identify the specific relationships and influence mechanisms between microstructure and mechanical properties of coatings. Annealing had three main effects on the mechanical properties of TiAlSiN coatings: grain coarsening, phase transformation, and surface oxide formation. Annealing resulted in grain coarsening, which improved the toughness of the coatings. The mechanical properties of TiAlSiN coatings were affected by the phase structure when phase transitions occurred during annealing. Additionally, the significance of the synergistic effect of improving measures on the mechanical properties of TiAlSiN coatings was emphasized. Finally, it was suggested to conduct deep research in future on improving mechanical properties of TiAlSiN coatings from basic theory and cooperation effect of various improvement actions. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.