预制表面梯度应变层增强高铁制动盘的耐磨性能

Wear Resistance of High-speed Railway Brake Disc Reinforced via Prefabricated Surface Gradient Strain Layer

随着客运铁路高速化,列车制动盘的磨损日益加剧,严重威胁列车服役的安全性。为了提高低碳马氏体钢制动盘的耐磨性,采用表面机械研磨处理(SMAT)技术在材料表面制备梯度组织,进而延长材料的服役寿命。结果表明:经SMAT处理后,样品表面形成厚约180μm的梯度应变层,切应变沿深度呈梯度分布。板条马氏体被挤压成塑性流线,在最表层形成亚微米晶和条状结构。微米划痕试验发现,样品表层材料的硬化率和摩擦性能随着深度呈梯度变化,耐磨性相比基体增强了1.2倍。在循环应力作用下,靠近样品表面的马氏体晶粒被细化,最表层材料的位错密度比基体提高了14.6倍,从而提高了制动盘钢的表面硬度和耐磨性。此外,与其他铁路耐磨材料相比,样品表现出较高的应变硬化速率。研究成果可为制动盘梯度应变层的工程应用提供参考。

With the rapid development of passenger railways,the service environment of the train is becoming increasingly severe,affecting the braking system’s stability.As one of the critical parts of the braking system,the wear damage of the brake disc of the high-speed rail seriously threatens the safety and comfort of electric multiple unit(EMU)trains.Fabrication of a gradient structure on the surface of a metal material can improve its wear resistance and prolong its service life.Specimens were obtained from a self-developed steel used in high-speed rail brake discs,whose heat treatment process includes a solid solution treatment,controlled rolling,quenching,and low-temperature tempering.A gradient strain(GS)layer was prepared on the surface of the specimen by a surface mechanical attrition treatment(SMAT)under room temperature and dry environment.In the SMAT,the test load was 800 N,the rotation speed was 400 rpm,and the treatment time was 30 min.The microstructure of the gradient strain layer was analyzed by scanning electron microscopy(Tescan MIRA3 XMU,USA).The surface layer and matrix of the specimens were analyzed by X-ray diffraction(Rigaku D/max2500pc,Japan).The mechanical properties and wear resistance of the GS layer were evaluated by a micrometer scratch tester(Rtec-HS100,USA).The matrix of the brake disc was mainly composed of a low-carbon lath martensite with a grain size of~62.23μm.The SMAT formed a gradient strain layer with a size of approximately 180μm on the specimens.The shear strain was distributed along the depth gradient.According to the deformation extent,the gradient strain layer could be divided into two zones:severe plastic deformation(SPD)and slight plastic deformation(LPD)zones.The SPD zone is below the surface,where the martensite lath is most refined,forming submicron crystals and strip structures on the top surface.The plastic flow lines are parallel to the wear surface.The LPD zone is close to the matrix.The martensite lath is extruded into a plastic streamline with a curved shape and shallow degree of refinement.Micrometer scratch tests on the SPD zone,LPD zone,and matrix show the mechanical and frictional properties of the GS layer.Compared to the matrix,the scratch width,depth,coefficent of friction(COF),and wear volume in the SPD zone are smaller.Moreover,the wear resistance coefficient in the SPD zone is increased 1.2 times(0.867),compared to that of the matrix(0.389).The position of the X-ray diffraction peak of the topmost surface layer is almost consistent with that of the matrix but slightly shifted to a larger angle.The peaks are considerably widened.This indicates that no phase transition occurred on the topmost surface,and no additional crystalline phase was produced.In comparison to the matrix,the microstrain of the topmost surface of the specimens is increased,while the lattice constant is decreased.The dislocation density of the topmost surface of the specimens(9.8×1015 m−2)is increased 14.6 times compared to that of the matrix(0.63×1015 m−2).Therefore,grain refinement and significant increase in dislocation density are the main reasons for the high hardening degree and excellent wear resistance of the GS layer surface of the brake disc steel.In addition,compared to the railway wear-resistant materials,the sample exhibits a higher strain hardening rate,which could provide a reference for the engineering application of the gradient strain layer of the brake disc.