Tribology is a frontier discipline that has developed rapidly in recent 50 years. It mainly includes the research fields of friction, wear and lubrication. Wear caused by friction is the main cause of mechanical equipment failure, and about 80% of the damaged parts are related to wear. Therefore, improving the wear resistance of parts can bring very considerable economic value. If wear is named according to the characteristics of dynamic process, it can be divided into sliding wear, rolling wear and so on. In different wear types, there may be a variety of action mechanisms on the interface, such as abrasive wear, adhesive wear, corrosion wear and fatigue wear. The wear mechanism of gray cast iron brake drum is mainly abrasive wear. In addition, there may be some adhesive wear according to the differences of materials and matching pairs. In the process of friction and wear, a large amount of mechanical energy is transformed into friction heat, which makes the brake drum produce metal oxidation and thermal fatigue, resulting in corrosive wear, which in turn affects the friction and wear performance of the brake drum.
Abrasive wear generally refers to the phenomenon that under the action of load, the harder abrasive particles impact or slide on the softer dual surface, so as to remove the material from the surface. It is the most common form of wear, and the furrow effect is its main wear mechanism, that is, micro cutting effect. Adhesive wear is a kind of wear caused by the local bonding between two solid surfaces in the process of relative sliding, and the sliding causes the shear fracture of these bonding points, resulting in the transfer of materials between the two surfaces or the loss from either surface. Corrosive wear is a kind of wear in which corrosion and wear work together in a corrosive environment. Corrosion wear is also called oxidation or chemical wear. Electrochemical reaction often occurs on the friction surface, resulting in loose corrosion products on the friction surface. It is very easy to peel off and form wear particles in the friction process. After peeling off, corrosion and wear will continue to occur repeatedly on the new surface, which is called corrosion wear. Fatigue wear is the phenomenon of severe plastic deformation and surface crack on the surface caused by the stress of cyclic contact, and surface peeling occurs after a certain number of cycles. Gear transmission and rolling bearings often fail due to fatigue wear. Thermal fatigue wear is relatively more complex. On the one hand, continuous thermal cycle makes the material produce thermal fatigue and change the material structure, on the other hand, it is also affected by sliding wear. Zhou Hong and others have done a lot of relevant research on this. Generally speaking, thermal fatigue is equivalent to continuous heat treatment of materials, which reduces the hardness and strength of materials to varying degrees, resulting in more serious workpiece wear, while the laser bionic model improves the wear after thermal fatigue to a certain extent.
The hardness of cast iron is mainly affected by the wear of graphite and graphite materials. The excellent wear resistance of gray cast iron in oil lubricated sliding state is due to the existence of graphite in the microstructure. On the one hand, because graphite is separated from the matrix and coated on the friction interface, it plays a role of solid lubrication; On the other hand, when graphite is separated from gray cast iron, many micro holes will be generated on the surface. Some people believe that these holes have good oil storage and play a favorable role in the boundary lubrication state. In the process of dry wear, on the one hand, graphite has a certain lubricating effect; On the other hand, the existence of graphite provides a large number of fine holes for the matrix, expands the contact area between the matrix and air, and reduces the oxidation resistance of gray cast iron. In the process of friction, the transformation of kinetic energy into internal energy accelerates the oxidation of the matrix, and the falling off of oxide film increases the wear of the matrix. At the same time, hard oxide particles further strengthen the wear of the matrix. There is a certain relationship between the total hardness of gray cast iron and the tendency of abrasive wear. With the increase of material hardness, the wear resistance of the material is improved accordingly.