Effects Of Laser Cladding Ceramic Powder On Thermal Fatigue And Friction-wear Resistance Of Vermicular Graphite Cast Iron

Brake disc is the critical component of railway vehicles disc brake. Vermiculargraphitic cast iron material has been widely used in railway vehicles brake disc due toits high tensile strength, large ductility, good thermal conductivity and low cost.During repeatedly braking process, brake disc and friction pair’s relative motionresults in mechanical energy transforming into heat energy. The surface of brake discproduces thermal stress because of its thermal cycling. Then hot cracks appear on thesurface of brake disc. Thermal fatigue and wear occur in the same time. When wearloss of brake disc exceed a certain value, the frictional force will be influenced. Thedecreasing of vertical pressure between brake lining and disc will affect the effect ofbraking and threaten personal safety. It concludes that thermal fatigue and wear arethe main failure mode of brake disc. In our country, either when the longest crack onsurface has reached fifty millimeter or the distance between crack and disc edge isless than ten millimeter, or the thickness of the brake disc has reduced to one hundredand twelve millimeter or the wear-causing reduction of thickness on one side of brakedisc is over7mm, the brake disc of high-speed train will stop for use. Now the life ofbake disc has been shortened because of hot crack and wear. To avoid a terribleaccident caused by the failure of brake disc, some brake discs which haven’t strictlymet the above scrapping standard have to be discarded earlier. So the enhancement ofthermal fatigue resistance and wear resistance of brake disc is a technologicalproblem which has to be solved urgently in railway system.We can get inspiration in the bionic fields. Some biont’s body surfaces are excellentmaterials which make them surviving in cruel nature world. Due to itssoft-hard-mixed structure, nacre can keep its shape from changing with very low wearloss under seawater washing and scouring. Leafs can maintain unbroken when theysuffer stormy weather. If observing the surface of leafs, we can discover that it is thestem distribution in leafs which can stop leafs from tearing. If the biologicalprototype is applied into material surface, then the material will be more durable.In this paper, laser cladding is used as an important method for biomimeticpreparation, comparing and studying the thermal resistant and wear resistant of lasercladding sample and laser melting sample, discussing the effect of different cladding material on thermal resistant and wear resistant of vermicular graphite cast iron,meantime considering the effect of different proportions of cladding material onthermal resistant and wear resistant of vermicular graphite cast iron. The resultsindicate that the addition of ceramic particles increases the nucleation and grainrefinement. Also the addition of hard particles strengthens the material dispersion. Solaser cladding can do better than laser melting in lessening crack initiation, blockingcrack propagation and reducing wear loss. The addition of different self-fluxing alloycoating will change the microstructure of bionic unit and enhance its strength andhardness. Wear resistant of the surface of vermicular graphite cast iron will improveeven more.