Some Improvements in Solid Lubricants Coatings For High Temperature Operations

In order to satisfy the growing request in solid lubrication for high temperatures, new solid lubricants are being developed. In this field the “quasi” solid lubricants and the soft nonabrasive film-forming lubricants constitute two important families. In the family of “quasi” solid lubricants an evaluation of lead monoxide-lead silicate coatings has been performed, particularly through the examination of the effect of minor addition of metallic materials, such as aluminum, iron and stainless steel, on the lubricant properties of coatings. These coatings are obtained through the melting and partial devitrification of lubricants. The lubricating properties of the coatings have been evaluated at different temperatures, with different load, with the rider wear and friction test. The system PbO-SiO2-Fe has shown the best properties (f = 0.2 at 650 C), and it may be utilized as a lubricant coating at temperatures to 650 C. In the family of soft nonabrasive film-forming lubricants, an evaluation of CaF2-base systems has been performed. In this case micrographic examinations, rider wear, and friction determinations have been carried out for evaluating the lubricating properties of the coatings. For applications that foresee temperatures over a wide range, the CaF2-BaF2-A g system is the most promising for lubricant coatings (f = 0.32 at 25 C1 f = 0.18 at 700 C); it may be used up to 800 C. For the temperature range 400–800 C, CaF2-BaF2 60–40 w/o system may be utilized for its low friction coefficient (at 600–700 C, f = 0.20). Some improvements in solid lubricants coatings for high temperature operations are discussed.