Research Progress on Nitriding Technology and Mechanism of Titanium Alloys

Titanium alloy has low density, high strength ratio, high corrosion resistance, high temperature resistance and other excellent properties, and has been widely used in aerospace, marine engineering, energy chemical industry and biomedical fields. However, the surface of titanium alloy has defects such as low hardness, poor wear resistance and insufficient fatigue resistance, which seriously limits its application range and field expansion. Therefore, the surface strengthening of titanium alloy has become one of the research hotspots. In recent years, many surface treatment technologies have been proposed for titanium alloys, including thermal spraying, cold spraying, electric spark strengthening, carburizing, CVD, PVD, ion implantation, laser alloying, etc. The coating prepared by thermal spraying has poor bonding strength with the substrate, and the cold spraying is likely to produce severe plastic deformation. The operation of EDM strengthening is simple, but it is likely to produce micro-cracks. Ion implantation is accurate and controllable, but the equipment cost is high. Each surface treatment technology has its own unique advantages and disadvantages and scope of application. When choosing surface treatment technology, it is necessary to make trade-offs and choices according to actual needs and conditions. Among many surface treatments, nitriding treatment has the advantages of fast penetration, small workpiece deformation, high chemical stability, simple process, etc., and can also be compounded with other treatment technologies, which is an effective method to improve the surface hardness, wear resistance, corrosion resistance and other properties of titanium alloys. Researchers have conducted a lot of research on this. However, the research on nitriding process of titanium alloy is relatively scattered and lacks a systematic and detailed summary. Based on this, the research status of gas nitriding, vacuum nitriding, ion nitriding, laser nitriding, rare earth catalytic nitriding, composite nitriding and other processes of titanium alloy were comprehensively reviewed in this paper, and the principle and characteristics of each nitriding process were briefly introduced. The effects of nitriding temperature, nitriding time, air pressure, nitrogen content, intermittent period, nitriding atmosphere, laser power, scanning speed and rare earth content on the microstructure and properties of the titanium alloy nitriding layer were emphatically described. Finally, the new nitriding process of titanium alloy is introduced, and the advantages and disadvantages of each nitriding process of titanium alloy in actual production were summarized. Some problems in the nitriding process of titanium alloy were also summarized, such as long production cycle, high cost, thin and brittle nitriding layer, and failure to withstand concentrated heavy loads. The future development direction of the titanium alloy nitriding process was prospected to some extent. In the future, the advantages of each nitriding process should be maximized, which tends to shorten the production cycle, optimize the nitriding structure, reduce the brittleness of the infiltration layer, improve the performance of the infiltration layer, and gradually eliminate the high energy consumption and polluting the nitriding process. It is proposed to comprehensive apply PVD, shot peening, ultrasonic nanocrystalline surface modification and other surface treatment technology, to provide useful reference for the development of titanium alloy nitriding layer performance optimization and surface strengthening technology. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.