【作者】 石红信；

【导师】 张永振；

【作者基本信息】 河南科技大学 ， 材料加工工程， 2020， 博士

【摘要】 随着电磁技术的发展,电磁设备得到了广泛的应用,其中的摩擦副工作于磁场环境中。磁场不仅能改变置于其中的铁磁性材料的力学性能和理化性能,而且能够改变摩擦副的摩擦面接触行为,从而影响到电磁设备中摩擦副的摩擦学性能和服役寿命。本文主要研究外加磁场对中碳钢干滑动摩擦磨损特性的影响途径及其关联性,探索磁场对材料摩擦学性能产生影响的关键因素和规律,以丰富干摩擦学内容,为磁场干摩擦学的实际应用、实现摩擦系统的主动控制提供理论依据。本文利用自制的销盘式摩擦试验机,进行了有、无磁场时中碳钢的摩擦磨损试验。以磁场摩擦过程中的磨屑行为及作用为目标,研究了外加磁场在不同条件下(捕获磨屑受到干扰、不同氧含量环境气氛)对中碳钢摩擦磨损特性的影响规律,分析了摩擦过程中磨屑和摩擦面的形貌与成分等的变化,阐明了磁场对中碳钢摩擦磨损特性的影响途径及其关联性,建立了磨屑行为模型和销试样摩擦面上氧化物改质层的形成模型等。磁场主要通过两种途径对中碳钢的摩擦磨损特性产生显著的影响。无磁场时销试样一直处于严重磨损状态,摩擦副主要发生黏着磨损和磨粒磨损;摩擦区域和盘试样摩擦面上的磨屑较少且分布均匀。磁场(8.7k A/m)作用下摩擦过程分为切削过渡阶段、研磨阶段和磁场摩擦稳定阶段;在研磨阶段磨屑逐渐细化、氧化并在摩擦区域和盘试样摩擦面上形成了磨屑捕获层,出现了严重-轻微磨损转变;在磁场摩擦稳定阶段销试样摩擦面形成了氧化物改质层,主要发生氧化磨损。磁场对中碳钢的减磨率可达90%以上,其影响途径主要包括研磨阶段的磨屑捕获层和磁场摩擦稳定阶段的氧化物改质层。磁场对中碳钢摩擦副的摩擦磨损特性的影响与其强度大小相关。随着磁场强度的增大,销试样磨损量逐渐减小并达到稳定。磁场强度为2.1k A/m时,销试样一直处于严重磨损状态;摩擦区域和盘试样摩擦面上磨屑较少且分布均匀,不能达成磁场摩擦稳定状态,主要发生磨粒磨损。当磁场强度超过4.3k A/m时,开始出现了严重-轻微磨损转变,摩擦区域和盘试样摩擦面上形成磨屑捕获层,捕获的磨屑能够填满且高出所覆盖的犁沟;销试样摩擦面有氧化物改质层生成,摩擦副主要发生氧化磨损。随着磁场强度的增加,磨屑捕获层的宽度逐渐增加,严重-轻微磨损转变越早,磁场摩擦稳定状态达成越快。磨屑捕获受到干扰时,磁场对中碳钢摩擦磨损特性的影响规律发生显著改变。当使用去磨屑装置时,盘试样摩擦面上残留的磨屑量显著减少;与正常条件下中碳钢的磁场摩擦相比,相等强度磁场时该条件下销试样的磨损量显著增大,无严重-轻微磨损转变;销试样摩擦面无氧化物改质层产生,摩擦副主要发生磨粒磨损;磨屑捕获受到干扰引起的磁场对中碳钢摩擦磨损特性影响规律的改变与磁场强度无关。磁场对中碳钢销/302钢盘摩擦副的摩擦磨损特性有一定影响,而影响规律与其对中碳钢摩擦副的影响规律相反。磁场(17.4k A/m)作用下销试样一直处于严重磨损状态,无严重-轻微磨损转变,其磨损程度大于无磁场时该摩擦副中销试样的磨损程度;盘试样摩擦面和摩擦区域残留有少量的磨屑,销试样摩擦面无氧化物改质层形成,摩擦副主要发生了磨粒磨损。环境气氛氧含量对中碳钢摩擦副的摩擦磨损特性有一定影响。无磁场时,当环境气氛氧含量为0.2%-21%时,随其氧含量的增加,磨屑氧化程度以较小幅度增加,销试样磨损量增大,磨损机制由黏着磨损(0.2%氧含量)转变为磨粒磨损;当氧含量为100%时,磨屑氧化程度较大,销试样磨损量显著减小,出现了严重-轻微磨损转变,主要发生了氧化磨损。磁场(8.7k A/m)作用下,当环境气氛氧含量为0.2%时,磨屑氧化程度较低,无严重-轻微磨损转变,主要发生了黏着磨损;当环境气氛氧含量超过0.5%时,磨屑氧化程度较大,摩擦过程出现了磨屑研磨阶段和磁场摩擦稳定阶段,发生了严重-轻微磨损转变,主要发生氧化磨损;磨屑氧化程度越大,研磨阶段和严重-轻微磨损转变发生越早。磨屑捕获对摩擦过程磁场摩擦稳定状态维持动态平衡有重要的作用。达到磁场摩擦稳定状态的中碳钢摩擦副在无磁场的摩擦过程中,盘试样摩擦面和摩擦区域不能有效捕获磨屑;销试样摩擦面上的氧化物改质层逐渐消失而呈金属亮白色,改质层的减磨时间约为400s,发生了轻微-严重磨损的转变。摩擦区域形成磨屑捕获层且磨屑发生一定程度的氧化是磁场对中碳钢起到减磨作用并使摩擦稳定状态的达成的前提和基础。磁场作用下中碳钢摩擦过程中的残留磨屑经历形成与捕获、伴随盘试样运动、研磨和连接四个连续阶段并反复进行;磁场强度、磨屑大小和成分、盘试样材料对磨屑的捕获均有重要影响;磨屑与犁沟、磨屑与磨屑之间发生冶金结合在销试样摩擦面不连续的犁沟中形成了氧化物改质层。更多还原

【Abstract】 With the development of electro-magnetic technology,a variety of electromagnetic equipments have been widely used,in which the friction pairs work in the the presence of magnetic field.The magnetic field can not only change the mechanical and physical-chemical properties of the ferromagnetic materials,but also alter the contact behavior between the friction surface of the friction pairs,which the tribological characteristics and service life of the friction pairs in electro-magnetic equipment are affected.The ways of influence of external magnetic field on the dry sliding friction and wear characteristics of medium carbon steel and their relevance were investigated in this paper.The key factors and regularities that magnetic field affects the tribological properties of materials were explored.This may help to enrich the contents of dry tribology and provide theoretical basis for the practical application of dry tribology under magnetic field and the active control of friction system.The friction and wear tests of medium carbon steel with and without magnetic field were carried out by using self-made pin-and-disc friction tester.Aiming at the behavior of wear debris and its function in the magnetic-friction process,the effects of magnetic field on the tribological properties of medium carbon steel under various conditions(the wear debris capture is interfered and the oxygen content changes in environmental atmosphere)were studied.The morphology and composition of wear debris and friction surface during friction were analyzed.The ways of influence of external magnetic field on the friction and wear characteristics of medium carbon steel and their relevance were clarified.On the above foundation,the wear debris behavior model and the formation model of the oxide modified layer on friction surface were established.The magnetic field has a significant effect on the friction and wear characteristics of medium carbon steel through two ways.When there is no magnetic field,the pin specimen has been in the state of severe wear during friction.The wear type of friction pairs is mainly abrasive wear and adhesive wear.The wear debris on the friction zone and the friction surface of the disk specimen is less and evenly distributed.Under the action of magnetic field(8.7k A/m),the friction process can be divided into such three stages as cutting transition stage,grinding stage and magnetic-friction stabilization stage.In the grinding stage,the wear debris became gradually small and oxidized,and the wear debris capture layer formed on the friction zone and the friction surface of disk specimen.And then the severe-mild wear transition occurred.In the magneticfriction stabilization stage,the oxide modified layer formed on the friction surface and the oxidation wear occurred between the friction pairs.The wear reduction rate of magnetic field for medium carbon steel can reach more than 90%,and its influence ways mainly include such two kinds of wear debris capture layer in grinding stage and oxide modified layer in magnetic-friction stable stage.The extent of influence of magnetic field on the friction and wear characteristics of medium carbon steel friction pairs have do with its intensity.With the increasing of magnetic field intensity,the wear of pin specimen decreased gradually and reached stability.When the magnetic field intensity is 2.1k A/m,the pin specimen has been in a state of severe wear during friction.The wear debris on the friction zone and the friction surface of disk specimen was less and evenly distributed.No magnetic-friction stable state reached,and the abrasive wear occurred between the friction pairs.When the magnetic field intensity is greater than 4.3k A/m,the severe-slight wear transition began to occur.The wear debris capture layer was formed on the friction zone and the friction surface of the disk specimen.The capture wear debris filled up and was higher than the grooves on the frction zone.The oxide modified layer was formed on the friction surface of pin specimen,and the oxidation wear occurred between the friction pairs.With the increasing of the magnetic field intensity,the width of the wear debris capture layer increased gradually,and the earlier the severe-mild wear transition occurred,the faster the magnetic-friction stable state reached.When the wear debris capture is disturbed,the regularities of influence of magnetic field on the friction and wear characteristics of medium carbon steel friction pairs change significantly.The residual debris on the friction surface of the disc specimen significantly reduced when the removal wear debris device was adopted during friction.Compared with the magnetic friction of medium carbon steel under normal conditions,the wear amount of pin specimen increased significantly under magnetic field of the same intensity,and no severe-mild wear transition occurred in the friction process.No oxide modified layer formed,and the abrasive wear occurred between the friction pairs during friction.The influence of magnetic field on the friction and wear characteristics of medium carbon steel was independent of the magnetic field intensity when the wear debris capture was disturbed.The magnetic field has a certain influence on the friction and wear characteristics of medium carbon steel pin/302 steel disk friction pairs.However the influence regularity is different from that of medium carbon stee friction pairs.When the magnetic field intensity is 17.4k A/m,the pin speciemn was in a serious wear state,and no severe-mild wear transition occurred in the friction process.The wear extent of the pin specimen was greater than that without magnetic field.The less wear debris remained on the friction zoneand friction surface of the disk spenimen.There is no oxide modified layer on the friction surface,and the abrasive wear occurred betweeen the friction pairs.The oxygen content in the friction atmosphere has a certain influence on the friction and wear characteristics of medium carbon steel friction pairs.When there is no magnetic field and the oxygen content of friction atmosphere is 0.2%-21%,with the increasing of oxygen content,the oxidation degree of wear debris increases slightly,and the wear amount of pin specimen increased.The wear mechanism transformed from adhesive wear(0.2% oxygen content)to abrasive wear.When the oxygen content is 100%,and the oxidation degree of wear debris was higher.The wear of pin specimen decreased significantly.The severe-slight wear transition arose,and the oxidation wear occurred between the friction pairs.When the oxygen content of friction atmosphere is 0.2% in the presence of magnetic field(8.7k A/m),the oxidation degree of wear debris was low,and no severe-mild wear transition occurred.The adhesive wear occurred between the friction pairs.When the oxygen content of the friction atmosphere is more than 0.5%,the oxidation degree of the wear debris is relatively high.In the process of friction,the grinding stage and the magnetic-friction stable stage occurred,and severe-slight wear transition arose.The oxidation wear occurred between the friction pairs.Moreover,with the increasing of oxidation degree of the wear debris,the occurrence time of grinding stage and that of severe-mild wear transition advanced.The capture wear debris plays an important role in maintaining the dynamic balance of the magnetic-friction stable state.During the friction process of the friction pairs of medium carbon steel in the magnetic-friction stable state without magnetic field,there was almost no residual wear debris on the friction zone and friction surface of the disk specimen.The oxide modified layer on the friction surface of the pin specimen gradually disappeared and the contrast of pin friction surface appeared metallic-bright white.The anti-wear time of the oxide modified layer was about 400 s,and then the mild-severe wear transition occurred.It is the premise and foundation for anti-wear of medium carbon steel and achievement of the magnetic-friction stable state owing to magnetic field that a debris capture layer is formed on friction area and the wear debris is oxidized to approprite certain extent.The wear debris movement during friction of medium carbon steel under the appropriate magnetic field can be divided into four continuous stages: formation and adsorption,movement with disc specimen,grinding and joining.In the process of wear debris movement,such physical and chemical changes as refinement,oxidation and agglomeration take place gradually.The magnetic field intensity,the size and composition of wear debris and material of disc specimen have important influence on the wear debris capture.The oxide modified layer can be formed in the discontinuous groove by metallurgical bonding between the wear debris and groove,and among the wear debris.The subsurface layer of the pin specimen caused by capture wear debris layer is mainly composed of deformed pearlite in the magneticfriction process,which can improve the anti-wear of the pin specimen to a certain extent.更多还原