Wear performance of talc-filled bismaleimide/aluminum sliding pairs

Abstract: The sliding friction and wear performance of dual maleic anhydride imide composites filled with different amounts and particle sizes of steatite against hard aluminum was studied on a disc friction and wear testing machine. Scanning electron microscopy analysis was used to explore the mechanism by which steatite regulates the frictional properties of dual maleic anhydride imide. The results show that with the increase in the amount of steatite and the decrease in particle size, the wear resistance of dual maleic anhydride imide and aluminum rings improves, and the sliding friction coefficient decreases; the improvement in wear resistance of the sliding pair due to steatite is because it promotes the formation of a strong transfer film of dual maleic anhydride imide on the surface of the aluminum ring. Introduction: The friction and wear performance of inorganic filler-filled modified polymer-based composites has always been a hot topic in the study of composite tribology. However, most studies focus on thermoplastic polymers, with relatively few on thermosetting polymers. The mechanism by which fillers affect polymer friction and wear has also been proposed. Dual maleic anhydride imide resin (referred to as BMI) is a new type of thermosetting resin that not only has excellent high-temperature and moisture resistance but can also be manufactured using similar molding processes to epoxy resins. It has advantages such as low cost, high elastic modulus, suitable hardness, and good bonding properties. It was first applied in the aerospace industry and has been increasingly used in civil industries as a high-temperature engineering plastic in recent years, as its heat resistance is superior to that of phenolic resins, making it a potential adhesive for organic friction materials. However, experiments have found that BMI has a high dry friction coefficient and experiences severe adhesive wear with counterpart materials, leading to the selection of steatite powder as a friction modifier. Steatite is a natural mineral filler that is low-cost and widely sourced, with needle-like crystal structures that also provide short fiber reinforcement. Adding it to some polymers can not only improve the wear resistance of the polymers but also enhance their friction properties, although reports on its tribological performance when added to BMI are still lacking. This paper investigates the effects of varying amounts and particle sizes of steatite on the sliding friction and wear performance of BMI against hard aluminum, exploring the feasibility and mechanism of steatite in regulating the tribological characteristics of BMI. 2 Experimental Section 2.1 Sample Preparation Materials: Steatite powder with particle sizes of 12-15μm, 8-10μm, and 1-5μm, referred to as 1#, 2#, and 3# respectively. The main components are SiO2 and CaO with a Mohs hardness of 4.5, provided by Harbin Institute of Technology's School of Materials Science; dual maleic anhydride imide HF-9401 (referred to as BMI) was developed by the Department of Chemistry at Harbin Institute of Technology, with a Rockwell hardness HRM of 122. Sample Preparation: The steatite powder was cleaned and dried using a mixture of acetone and alcohol, producing powders with mass fractions of steatite of 30%, 50%, and 70%, which were then pressed into ring-shaped BMI binary system samples with an outer diameter of 32 mm, inner diameter of 22 mm, and thickness of 7 mm. The upper and lower end faces were polished with 800# (particle size approximately 23.5 μm) water sandpaper, repeatedly rinsed with ethanol, and dried to create friction samples. 2.2 Testing Method The sliding friction tests were conducted on an MPX-200 disc friction and wear testing machine, using a ring-on-ring configuration. The counter sample ring was made of hard aluminum alloy LY12, with dimensions of outer diameter 34 mm, inner diameter 20 mm, and thickness 7 mm. Both end faces were polished with 800# water sandpaper, cleaned, and dried. The normal pressure was set at 60 N, the spindle speed at 370 r/min, and the friction time at 30 min. The wear amount of the samples was determined by the mass difference before and after wear, accurate to 0.0001 g, with the wear rate expressed in g/Nm. The tests were conducted under dry friction conditions at room temperature. 3 Results and Discussion The friction coefficient of BMI composites filled with steatite varies with the amount of steatite. It can be seen that adding steatite powder to BMI gradually reduces the friction coefficient as the amount increases. Additionally, it was found that steatite powders of different particle sizes have varying effects on reducing friction, with larger particle sizes resulting in less reduction in the friction coefficient. Steatite is an inorganic filler that can lower the friction coefficient of BMI, which is an interesting phenomenon worthy of further study. According to the principles of tribology, the friction between sliding pairs arises from molecular and mechanical interactions at the friction surfaces. When pure BMI is in friction with the aluminum ring, the friction mainly comes from the molecular adhesion between the micro-protrusions on the contact surface, with mechanical action being relatively weak. When steatite is filled into BMI, it reduces the adhesive area between pure BMI and the aluminum ring, leading to a decrease in adhesive friction. Furthermore, due to the small particle size and lower hardness of steatite powder, especially the steatite powder that wears off during friction may act as a rolling support, resulting in no significant increase in mechanical action between the BMI composite and the aluminum ring. Therefore, the friction coefficient of steatite-filled BMI composites decreases with the increase in the amount of steatite used. Figure 2 shows the wear rate of BMI composites and aluminum rings as a function of the amount of steatite powder. It can be seen that adding steatite powder to BMI can significantly reduce the wear amount of BMI and the aluminum test ring, and as the amount of steatite powder increases and the particle size decreases, its wear-reducing effect increases. The wear resistance of steatite powder is mainly due to its short fiber-like inorganic filler structure, with a length-to-diameter ratio of 5:1 to 15:1, and its main components are CaO and SiO2. As mentioned earlier, the friction between pure BMI and the aluminum ring occurs through the formation of an adhesive transfer film, but this transfer film is not strong. After adding steatite powder, the tensile strength of the BMI composite increases, while the fine and hard steatite powder has a polishing effect, causing the oxide film on the surface of the aluminum ring to peel off, exposing fresh surfaces. Studies have shown that CaO and SiO2 can promote the formation of a strong transfer film of the polymer on the metal surface, further enhancing its wear resistance. This analysis can be confirmed by the SEM morphology of the wear surfaces of BMI composites and aluminum rings shown in Figure 3. From Figure 3a, it can be seen that the surface of the aluminum ring has a brown transfer film and very fine polishing stripes, while Figure 3b shows that the friction surface of the BMI composite is attached and relatively smooth. Additionally, the needle-like crystal structure of steatite and its short fiber reinforcement can improve the toughness of the BMI matrix, increase its melt viscosity, and stabilize the molding dimensions. Testing the BMI composite with a steatite mass fraction of 50% showed that its Rockwell hardness HRM was 115, and the molding temperature increased from 210°C for pure BMI to 220-230°C. It can be seen that adding steatite to BMI has little effect on the hardness and high-temperature resistance of BMI. Therefore, utilizing the excellent performance of steatite as a friction modifier makes it feasible for BMI to become an organic friction material with excellent performance and heat resistance. This study provides a basis for optimizing the design of composite friction material formulations with comprehensive performance. Conclusion: 1. Steatite can improve the wear resistance of BMI, alter its friction characteristics, and with the increase in the amount of steatite and decrease in particle size, the wear resistance of BMI and the aluminum ring increases, and the friction coefficient decreases. However, when the amount exceeds 50%, the difference in this effect diminishes. 2. The improvement in wear resistance of BMI and the aluminum ring due to steatite is mainly related to the formation of a protective transfer film. The CaO and SiO2 in steatite can promote the formation of the transfer film of BMI on the surface of the aluminum ring, increasing the adhesion of the transfer film to the matrix.