| Brake drum is one of the most important components in the brake system of trucks, theproperty 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 islower,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 exceedscracked utmost. According a mass of research,we concluded that when brake drum wasinactive, the phenomenon of wide and deep cracks, as long as the height of drum, distributedon the inner surface of the failure drum was discovered. The thermal fatigue occurs inbraking process may cause the initiation and subsequent propagation of cracks, which isconsidered to be the main reason for the failure of brake drums. The fracture of brake drumdid 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 toinvestigate and enhance the thermal fatigue resistance of gray cast iron and make brakedrums with higher performance and longer service life.It is found by biomimetic reach that the nature creatures always choose the best way oftheir unsmooth shape, surface structure and component buildup to gain the best functionsthrough millions and thousands year's evolutions. It is the coupling functions that form thespecial features of the organism. Laser can be used to conduct selective and precisionmanufacture because the heat effective area is small, the direction of the beam is good andthe spot of the beam can be focused to the wave length degree. So, according to biologicalcoupling phenomenon and bionic coupling theory, we built the model of bionic couplingthermal fatigue resistance, and in this paper, laser technique was chosen to process cast ironsamples to obtain a regular hardness distribution on their surface to achieve the aim of improving the thermal fatigue resistance of gray cast iron finally.This paper investigated different alloy composition (including 25Ni75Cr, 50Ni50Cr,75Ni25Cr) and different types of self-fluxing alloy (including Fe30A, Ni45, Co50) oninfluencing law of biomimetic coupled cast of thermal fatigue properties.Finally, the conclusions are gained as follows:1,Laser alloying of Ni, Cr obtained with bionic body composition coupling unit isbasically the same, mainly from the primary phase and eutectic composition, in which theprimary phase for the austenitic and Ni, Cr dissolved in the Fe solid solution formation ofcrystals is for the M7C3 carbide, austenite, Ni-Cr-Fe solid solution composed of mixedorganizations; phase transition alloying elements do not enter the area only to change frommartensite + residual austenite + graphite composition.2,Obtained by laser alloying Bionic coupling unit for inhibiting the hot crack is betterthan laser melting treatment,laser alloying 75Ni25Cr can effectively reduce the crackinitiation and expansion, thermal fatigue properties of the best, followed by 50Ni50Cr,25Ni75Cr; thermal fatigue test results show that the thermal cycle 2400 times, laser alloying75Ni25Cr, 50Ni50Cr, 25Ni75Cr more smooth specimen the total number of cracksdecreased 50.0%, 53.6%, 57.1%, crack propagation rate of decline were 50.0%, 68.8%,78.6%.3,Laser cladding Fe30A cladding layer more complex organizational structure, solidsolution from the primary phase, white and gray skeleton consisting of a total crystal, blackstrip or block the distribution of compounds and the diffusion of small white blockcompounds, of which the matrix for the Fe - Cr-Ni solid solution, and M7C3 eutectic solidsolution is a mixture of compounds, compared with M23B6, Fe3Ni3B; Laser Cladding Ni45matrix by Fe, Cr alloying elements dissolved in the formation of a wide range of Ni solidsolution composition, the distribution in the matrix on a variety of compounds, such ascarbide Cr23C6, M7C3, boride CrB, Ni4B3; laser cladding Co50 even small organizations tothe dendrite and eutectic mixture pluralistic organizations, matrix containing chromium,nickel, cobalt-molybdenum solid solution, the existence of a large number of M7C3 to provetheir might be a product of eutectic transformation, as well as Cr23C6 and Fe3Ni3B compounds dispersed in the matrix; hardness distribution by the cladding zone to graduallyreduce the matrix, laser cladding Co50 reach the highest hardness HV0 .2737.2, LaserCladding Ni45 up to HV0.2725.1, up to Fe30A laser cladding HV0.2535.9, heat-affected zonein between HV0.2450 ~ 500.4,Laser cladding unit to strengthen access to the bionic thermal coupling of the fatigueproperties of the sample was superior to laser melting treatment, one of laser cladding a largeextent, improve the biomimetic C050 coupling of gray cast iron heat fatigue performance, inthe hot cycle , the number of hot cracks is always at least, has always been the shortest inlength, followed by laser cladding Ni45, laser cladding Fe30A, laser ,melting worst specimen;after 500 times thermal fatigue, changes of hardness with the thermal fatigue before, butthose hot fatigue before the decrease in laser cladding zone C050 dropped by an average ofHV0.237.0, laser cladding Ni45 area dropped by an average of HV0.275.0, laser claddingFe30A area dropped by an average of HV0.275.2, Laser Melting District Average declineHV0.2221.7; a slight decrease in heat-affected zone, located in between the HV0.2400 ~ 450.5,Laser alloying, laser cladding and laser melting processing unit to enhance theachievement of the purpose, have shown a certain crack resistance, but against theimprovement of thermal fatigue properties of the degree is different, mainly due to laseralloying and laser cladding to enhance the mechanism of cell body and different laser melting,laser alloying and laser cladding as a result of alloying elements added by solid solutionstrengthening of alloying elements and alloy compounds precipitate diffusion unit furtherstrengthened, so as to further enhance the thermal fatigue properties.
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