The Integration Research Of Thermal Fatigue Resistance And Wear Resistance Of Bionic Vermicular Cast Iron Processed By Laser In Water

It is generally used in the manufacture of train brake by countries around theworld based on its excellent property under conditions of dry sliding friction withstrong thermal effects, such as high friction coefficient, low wear rate and excellentthermal fatigue performance, and so on. Moreover its manufacturing process issimple and the cost is low. The main failure forms of brake disc are wear andthermal fatigue. The laboratory research of material wear properties and its thermalfatigue properties is usually independent. In order to make basic research inlaboratory more close to the practical application, the integration research ofthermal fatigue resistance and wear resistance is proposed, the thermal fatigueresistance of bionic vermicular cast iron processed in water is studied after its wearresistance has been studied.With the improvement of train speed, the higher performance of the brake discmaterials is need. According to the bionic model which was built by materialscoupling with forms, using laser surface local processing technology, a new methodto improve the performance of steel materials have been proposed in recent years,which can process bionic units on the surface of materials and make the bionicunits combine with the matrix to form the structure which has similar to the biological surface and has wear resistance, fatigue resistance. The bionic units onlyexist in the shallow range of the surface; while for train brake disc, their wear limitis7mm on unilateral side. The effect of laser bionic processing on improving itsservice life is limited, so the wear of brake disc is expected to return to originalstate, when the bionic units are run out, the overall stability of the brake disc willbe affected. Moreover the brake disc is one kind of parts which are difficult toreplace, because of its quality and installation location. It also needs to improve theservice life of the brake disc. Analysis from the perspective of the bionic principle,the bionic surface processed by laser bionic processing is the non-smooth surfaceformed by materials coupling with forms which characteristic is hard phasecombines with soft phase. Its overall performance can be improved by enhancingthe performance of bionic units. Therefore the laser bionic processing in water wasused to further improve the performance of bionic units.The researches of thermal fatigue properties and wear resistance areorganically combined. The influence of thermal fatigue on wear performance isstudied. The connection between the quality of the bionic units and the overallperformance of bionic specimens also is discussed. All of above provide theoreticaland experimental basis for the engineering application of laser bionic processing inwater.The conclusions are that:1. Using shells and leaves as biological prototype which have the performanceof wear resistance and fatigue resistance, the bionic surface on vermicular cast ironwhich has striped bionic units were obtained by water process. The microstructureof bionic unit is refined and its micro-hardness is raised from670HV to920HV.2. The time of the first thermal crack appearing on the bionic vermicular castiron processed in water lag behind than that processed in air, the time is200times thermal fatigue cycle. Under the same thermal fatigue condition, the thermal cracknumber of bionic vermicular cast iron processed in water is always less than that ofbionic vermicular cast iron processed in air. Yet the longest length of cracks islonger than that of processed in air. The laser bionic treatment in water improvesthe resistance to thermal cracks initiation. But more cracks of bionic unitsprocessed in water increase the chances that the cracks on unit and matrix cracksare overlapped together. So the resistance to thermal crack propagation of thebionic vermicular cast iron reduces.3. Under the same wear conditions, the wear resistance of bionic vermicularcast iron processed in water is increased by43%.4. The wear tests of bionic vermicular cast iron undergone thermal fatiguetests show that with the increasing of thermal cycles or thermal temperatures thewear resistance decreased and the wear loss linear increased. The equation of linerregression of wear loss belong to un-treated vermicular cast iron is y=0.554x-11.48,R2=0.9833, the x is used to show thermal fatigue cycles and the y is used to showwear losses. The equation of liner regression of wear loss belong to bionicvermicular cast iron processed in air is y=0.0363x-6.9, R2=0.9791, and that belongto bionic vermicular cast iron processed in water is y=0.0307x-8.08, R2=0.9812.From the slope of the trend lines, the slope of specimen treated in water is the least,so under the same wear conditions, its growth of wear loss is the least, and its wearresistance is the best.5. In the thermal fatigue tests, the microstructure of the bionic units broke, andeven layered dissection, it caused the wear resistance of the bionic vermicular castiron dropped. Under the same conditions, the wear resistance of bionic vermicularcast iron processed in water is always better than that of processed in air, becausetheir microstructure changes relatively lag behind. 6. After auxiliary process, the number of bionic units’ cracks and the chance ofthe units’ cracks lap over the matrix’s cracks reduced. The order of effects from bigto small is: electric pulse treatment﹥water bionic treatment﹥twice laser treatment﹥after heat treatment﹥preheat treatment.7. Twice laser process and electric pulse treatment can make bionic unitsprocessed in water formed network cracks which have less cross cracks. Theresistance to thermal crack propagation of the bionic vermicular cast iron enhanced.After electric pulse treatment, the micro-hardness of bionic units is improved, itproduced positive effects on wear resistance of bionic vermicular cast ironundergone thermal fatigue tests.