Tribological Behavior of Ag-Doped Mo-12Si-8.5B Alloy from 25 to 600 ℃

With the continuous development of modern aerospace industry, the requirements for the operation temperature and service life of high-temperature materials are becoming higher. And the working conditions of materials are becoming more stringent. Therefore, the development and preparation of new ultra-high temperature structural materials is urgent. Mo-Si-B ternary alloys have become one of the promising new ultra-high temperature candidate materials because of their high melting point (2 000 ℃), high strength, high hardness and excellent high-temperature oxidation resistance. The Mo-12Si-8.5B (atom fraction/%) alloy, consisted of α-Mo-based, Mo₃Si, and Mo₅SiB₂ intermetallic compound reinforcement phases, has been extensively researched due to its excellent high-temperature strength, excellent creep resistance, and balance between high-temperature oxidation resistance. What’s more ,it is anticipated to be a key material in high-temperature applications. Al₂O₃ ceramics are often used in hybrid bearing components of high-performance jet engines. As the moving parts, the Mo-12Si-8.5B alloy and Al₂O₃ ceramics will experience dry friction relative sliding within a certain temperature range. However, according to the current research reports on the dry friction and wear characteristics of Mo-12Si-8.5B alloy at moderate temperatures (600 ℃) and below, the two important indicators for evaluating its tribological properties, the friction coefficient and the wear rate are still relatively high. Therefore, at the moderate temperatures and below, how to reduce the friction coefficient and wear rate of Mo-12Si-8.5B alloy and ceramic pairing pairs, and how to improve the effective lubrication and self-lubricating function of the alloy both provides strong theoretical support for the practical application of Mo-12Si-8.5B alloy in engineering. In this article, Mo-12Si-8.5B and Mo-12Si-8.5B-10%Ag alloys were prepared by spark plasma sintering method and the dry friction and wear properties of the two alloys paired with Al₂O₃ were tested at 25~600 ℃ using a high-temperature vacuum friction and wear tester. The results showed that compared with Mo-12Si-8.5B alloy, Mo-12Si-8.5B-10% Ag alloy exhibited lower friction coefficient and wear rate in the range of 25~600 ℃. The friction coefficient and wear rate of Mo-12Si-8.5B-10%Ag alloy could reach the minimum values of 0.41 and 1.14×10⁻⁵ mm³/(N·m) respectively at 600 ℃. At this time the friction performance of Mo-12Si-8.5B-10% Ag alloy was the best, which was related to the presence of lubricating phases, such as MoO₃, B₂O₃, SiO₂ and Ag₂MoO₄ on the worn surface of Mo-12Si-8.5B-10% Ag alloy, as well as the lubricating effect of Ag in the range of 25~600 ℃. In addition, the wear mechanism of Mo-12Si-8.5B-10% Ag alloy was mainly adhesive wear and peeling wear within the range of 25~200 ℃. In the middle temperature range of 400~600 ℃, it was mainly adhesive wear and oxidation wear. This article provided basic data and theoretical support for in-depth research on the friction and wear theory of Mo-Si-B alloy, realizing the self-lubricating function of Mo-Si-B alloy in a wide temperature range and practical applications.