Study on tribological properties of iron sulfide coatings prepared by a sol-gel method

Abstract

The methods of surface chemical heat treatment, such as low temperature electrolysis sulfuration and salt bath sulfuration or low temperature ion sulfuration [1–4], are usually adopted to prepare FeS solid lubrication coatings, which possess good anti-friction properties. But these methods are all relatively complicated. As a wet chemosynthesis method, the sol-gel method possesses a lot of advantages. The facility required is simple, the process is easy to control and the purity and homogeneity are high. The method has been extensively used to prepare wear-resistance coatings [5–8]. But as yet the research results, using the method to prepare anti-friction coatings, have not been reported. The authors prepared the FeS solid lubrication coatings by a sol-gel method, besides investigated their tribological properties. The substrate material was 1045 steel (AISI). It was heat-treated by quenching and low temperature tempering, the hardness was HRC55 and the surface roughness Ra was 3.2 μm. The powder size of FeS and zinc was all about 10 μm. The volume of the solvent, patented product (ZM-1 model), was 500 ml. The total weight of the solute, both FeS and zinc powder, was 100 g. The solvent and solute were mixed and stirred evenly for 15 min to form the sol. In the sol, FeS was used as solid lubricant and Zn was used to disperse evenly the FeS powder and enhance the wet ability of FeS powder to the substrate. To compare the difference of their tribological properties, four kinds of sol with different FeS contents were prepared. The FeS contents were 10 g, 20 g, 30 g and 40 g respectively. As a correspondence the zinc contents were 90 g, 80 g, 70 g and 60 g respectively. A special equipment was utilized to spray the sol homogeneously onto the surfaces of 1045 steel about 500 μm thick. These coatings were dried in an insulation can (100 ◦C). Friction and wear tests were carried out on a ball-ondisc tester (QP-100 Model). The upper samples were 52100 steel ball with diameter 12.7 mm and hardness of 770 HV. The lower samples were the 1045 steel discs prepared with the FeS coatings, with dimensions of φ 60 × 5 mm. All tests were carried out at the condition of room temperature and atmospheric environment, lubricated with No. 40 lubrication oil (no additives). The