| Brake drum is one of the most important components in the brake system of trucks, the property of which affects the brake property and even security of brake system of trucks. Gray cast iron is widely used as the material for brake drums, and it has no elasticity limit. So, a little stress may lead to plastic yield. In addition, the intensity of gray cast iron is lower,and it is easily exceeded by the super-coated stress of local area when it works. Also, gray cast iron is brittleness material. So, it appears cracks when thermal stress exceeds cracked utmost. According a mass of research,we concluded that when brake drum was inactive, the phenomenon of wide and deep cracks, as long as the height of drum, distributed on the inner surface of the failure drum was discovered. The thermal fatigue occurs in braking process may cause the initiation and subsequent propagation of cracks, which is considered to be the main reason for the failure of brake drums. The fracture of brake drum did a lot of harm to our country, such as money, source, manufacture, manpower and so on, and caused thousands of accidents and lawsuit-cases. Therefore, it is important and urgent to investigate and enhance the thermal fatigue resistance of gray cast iron and make brake drums with higher performance and longer service life.It is found by biomimetic reach that the nature creatures always choose the best way of their unsmooth shape, surface structure and component buildup to gain the best functions through millions and thousands year's evolutions. It is the coupling functions that form the special features of the organism. Laser can be used to conduct selective and precision manufacture because the heat effective area is small, the direction of the beam is good and the spot of the beam can be focused to the wave length degree. So, according to biological coupling phenomenon and bionic coupling theory, we built the model of bionic coupling thermal fatigue resistance, and in this paper, laser technique was chosen to process cast iron samples to obtain a regular hardness distribution on their surface to achieve the aim of improving the thermal fatigue resistance of gray cast iron finally.The paper investigated the shape and configuration, XRD and microstructure of bionic coupling units with different matrix structure which included different graphite shape(include HT200,RT380 and QT600) and carbon content(include 3.05%,3.45% and 3.70%), and studied the performance of thermal fatigue resistance of cast iron with above matrix structure. In addition, we adopted HT200 as object to investigate that the thermal fatigue resistance of bionic coupling cast iron with different distributing of units (include the connect form,density of distributing,angle of distributing), and studied the thermal fatigue resistance of bionic coupling units compared with the matrix of untreated sample. Finally, the conclusions are gained as follows:(1) After laser processing, the microstructure of biomimetic coupling units was obviously different from matrix and consisted of melt zone and phase change zone. The melt zone did not have graphite and formed ledeburite, but the phase change zone had some graphite and generated martensite. The size of biomimetic coupling unit was affected by the heat conductivity of material, and the better the heat conductivity was, the bigger the size of unit was.(2) Biomimetic coupling units had better thermal fatigue resistance compared with untreated sample. It not only can delay the initiation of thermal crack, but also can postpone the propagation of thermal crack. When the distributing shape of units was different, the thermal fatigue resistance of biomimetic coupling sample was different. When the connected form (including nail form, dam form and grid form) between units and matrix was grid form, grid unit was just like the dam which distributed reticulate, and the area of dam was the biggest, and the area for initiation and propagation of cracks were the smallest, so the sample had the best thermal fatigue resistance.(3) When the distributing density of units was different, not the bigger the density was, the better the thermal fatigue resistance was, and the spacing between two adjacent units was 2mm, the biomimetic coupling sample had the best thermal fatigue resistance for it's reasonable biomimetic structure and reasonable spacing; when the angle(including 0°,45°and 90°) between the direction of units and the propagating direction of thermal crack was 45°, the sample had the best thermal fatigue resistance, because that it possessed the predominant characteristics of 0°sample and 90°sample at the same time.(4) When matrix was different, the thermal fatigue resistance of biomimetic coupling sample was different. With the increase of carbon content (including 3.05%, 3.45%, and 3.70%) of matrix, the thermal fatigue resistance of biomimetic coupling sample enhanced gradually, that is , biomimetic coupling sample with 3.70% carbon content has the best thermal fatigue resistance. Thermal fatigue resistance of biomimetic coupling samples with different graphite shapes(gray cast iron HT200,the vermicular cast iron RT380,spherical graphite iron QT600)was different, and it was affected mainly by graphite shape. Because thermal cracks were all initiated at the place of graphite phase and main crack propagated along the graphite and the directions of their shortest distance. The thermal fatigue resistance of QT600 was best, and then was RT380, and the HT200 was worst.
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