Interaction Between Thermal Fatigue And Friction Wear Of Gray Cast Iron With Enhanced Units By Laser Cladding

Railway is the sinews of national economy. As railway transportation towards tothe higher speed, safe operation of trains has became a top priority in China. Themore strict requirement for the braking performance of trains is needed, because thetraditional materials of brake disks have already couldn’t meet the needs. So the studyof the new train brake disc material has very important significance.When the train brake disc is in the working state, the surface of the brake discproduces temperature difference, because the friction pair is incomplete. It can causecracks and thermal fatigue in the brake disc, so the friction and wear of the brake discis accompanied by thermal fatigue. In the state of thermal fatigue, the changes of themicrostructure lead to decrease in hardness, so it will inevitably have some impact onthe friction and wear properties of the brake disc.Biological in nature has been through a long evolutionary process, so they has astrong ability to adapt the environment. In some respects, some peculiar performancethat they have is much more excellent than the one that our design. According to thetheory of bionics, we imitate shell surface characteristic and constitution to processthe enhanced units with different cladding materials、different shapes and differentspaces in gray cast iron brake disc surface by the method of laser cladding. Comparedwith the unit formed by laser melting, the enhanced unit formed by laser cladding hasa greater increase in hardness and depth, and because of the addition of alloy elementswhich changes the composition of matrix, the enhanced unit specimen has a betterthermal fatigue performance. In this thesis, bionic gray cast iron samples should befirstly through1000、2000、3000、4000thermal cycles and then through wearresistance test. We study the impact on thermal fatigue-resistance and wear-resistanceby the enhanced unit, and the influence on wear-resistance by thermal fatigue. In thisthesis, we study the microstructure and hardness of the enhanced unit by laser cladding、the influence on thermal fatigue-resistance and wear-resistance by enhancedunits、the changes of microstructure and hardness of enhanced units before and afterthe thermal cycles、the impact on wear-resistance properties of bionic specimens bydifferent thermal cycles, and we can draw the conclusions as follows:(1)The tissue of enhanced units processed by laser cladding is very compact, andthe hardness of enhanced unit is higher than the unit processed by laser melting, so thehardness of enhanced unit is much more higher than the substrate and the enhancedunits and substrate form hard and soft white bionic non-smooth surface. The enhancedunits by different cladding materials have different microstructure and hardness.(2)The enhanced units can improve the thermal fatigue-resistance property ofbionic specimens: bionic specimens with grid-shape enhanced units has the bestthermal fatigue-resistance property; the thermal fatigue-resistance is better when thespace between the enhanced units is smaller; the specimens processed by lasercladding have better thermal fatigue-resistance property than the specimens processedby laser melting.(3)After thermal fatigue, the microstructure of the enhanced units changes and thehardness decreases.(4)The enhanced units can improve the wear-resistance property of the bionicspecimens, the higher hardness of enhanced units is, the better wear-resistanceproperty is.(5)The wear-resistance property of bionic specimens decreases after thermalfatigue, as the increase of thermal cycles, the wear-resistance property decreasesgradually.