Titanium alloys has many advantages such as high strength and low density, and has broad application prospects in aerospace and other industries, but its low hardness and poor wear resistance limit its further application. Physical vapor deposition (PVD) and chemical vapor deposition (CVD) can improve the surface hardness and wear resistance of titanium alloy, but these methods have disadvantages such as low efficiency. Laser nitriding of titanium alloy can quickly improve surface hardness and wear resistance of the titanium alloy, but the nitriding progress is complicated and many scientific and technical problems need to be solved. Domestic scholars have begun to pay attention to this research, foreign scholars have made some achievements. The current research focus on the mechanism of nitriding process and the effect of plasma on nitriding process. In recent years, foreign scholars have used high-speed imaging with different wavelengths of lenses to systematically study plasma, the conditions for the generation of nitrogen plasma as well as the role of plasma on energy transmission, prevent oxidation and the increase nitrogen content in nitrided layer have been deeply understood.At present, it is considered that nitrogen plasma is beneficial to laser nirtiding, and plasma is the core to obtain high quality of nitride layer. Based on the above research, a laser-sustained plasma nitriding method has been developed,in this method, nitrogen plasma is inducted by laser, nitriding is performed under the parameters of large laser power, large defocus distance and large scanning speed; the effects of process parameters such as defocus distance, scanning speed and nitrogen-argon ratio on laser-sustained plasma nitriding process were further studied. The laser-sustained plasma nitride layer is easy to crack, in order to avoid cracking of nitriding layer, two-step laser-sustained plasma nitriding method was also developed, the first step is use laser-induced nitrogen plasma to achieve a large amount of nitrogen content of the substrate; the second step is to remelt the nitrided layer by laser in argon plasma to eliminate cracks. The two-step nitriding method enhances the ability to control the performance of the nitrided layer, the nitrogen layer performance is better.In addition, a quantitative study on the nitriding process was carried out, it was found that the laser scanning speed is directly proportional to the time of molten pool on the surface of titanium alloy and the laser scanning speed is directly protortional to the nitrogen content of nitriding layer; the hardness of the nitrided layer and the dendrite content are also linear relationship; the wear resistance of two-step laser-maintained plasma nitride layer was studied, and the mechanism of enhanced wear resistance of nitrided layer was proposed. Research progress on laser-sustained plasma surface nitriding of titanium alloys are reviewed, the role of plasma, laser-sustained plasma nitriding and two-step laser-sustained plasma nitriding methods are introduced respectively, the key issues and effective research methods are proposed to provide reference for future research work. © 2020, Materials Review Magazine. All right reserved.
