【作者】 万轶；

【导师】 熊党生；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2008， 博士

【摘要】 摩擦磨损是机械设备失效的主要原因之一,大约80%的零件失效是由于各种形式的磨损引起的,磨损不仅消耗能源和材料,而且加速设备报废、导致频繁更换零件,对经济造成极大的损失。本文从改变材料表面形貌和组织对摩擦性能影响的角度出发,以端面密封材料的摩擦磨损形式为研究对象,利用摩擦磨损试验平台和ABAQUS有限元模拟分析了表面织构化的摩擦磨损行为及接触应力分布,为机械密封摩擦副的耐磨技术开发提供试验和理论依据。以现有科研成果和文献作为指导,利用波长为1064nm的Nd:YAG脉冲激光在摩擦副材料表面进行织构化处理,将高能量密度的脉冲激光等间隔作用于摩擦副材料表面并使之熔化,从而形成均匀分布的凹坑/凹槽结构,通过改变脉冲次数、能量和间隔,获得不同尺寸、形状及分布密度的表面织构。测试表面织构之间的硬度值;分析激光处理对材料的热影响效应;采用白光干涉三维轮廓仪表征织构的三维形貌;用扫描电子显微镜观察热影响区附近的熔化溅射状态。模拟密封摩擦副,对织构化密封材料PTFE/GCr15钢进行环/盘式摩擦磨损试验,测试不同摩擦配副和织构参数,如:直径、深度、间距、密度、形状等,对摩擦学性能的影响,得出最佳的微孔参数。通过ABAQUS有限元软件对滑动接触过程进行三维有限元数值模拟,分析了不同微孔直径、间距和分布密度下的等效应力。对表面织构化的45钢进行表面双辉等离子渗金属处理,纯铬/钼板作为源极,工艺参数为:极间距20mm、源极电压800V、试验温度880～900℃,渗铬时间4h、工作气氛为氩气。用光学金相显微镜观察合金渗层截面形貌;测试合金层截面的显微硬度;采用X射线衍射仪对合金渗层进行物相分析,用扫描电子显微镜和能谱仪测试渗层成分。试验结果表明:在贫油润滑条件下,激光织构化处理将密封材料摩擦副PTFE环/GCr15盘的摩擦系数由0.1降低到0.075,磨损率降低到光滑配副盘的2/3。织构化后,配副的PV值由6.5 MPa·m/s提高到16.4 MPa·m/s,最大PV值提高了1.5倍以上,油膜寿命延长了2倍以上。对两种类型表面织构（凹槽型/微孔型）的摩擦性能研究发现,油润滑下,微孔型织构的摩擦系数（0.065）低于凹槽型（0.08）,微孔型织构的存油能力优于凹槽型,沟槽型和微孔型的磨损率在10.0×10^-16m³/N*m左右,为光滑试样15.2×10^-16m³/N*m的2/3,且磨损寿命较光滑配副增大一个数量级。对于微孔化配副,摩擦系数和磨损率随微孔直径、深度的增大而减小,但过大的微孔直径对磨损率不利;随着微孔密度增大,磨损寿命增加,而摩擦系数和磨损率先减小后增大。结合微孔直径、深度、密度的分析可以得出:微孔直径为150μm、间距500μm、深度30～40μm、密度8～9%的织构化密封材料摩擦学性能最佳,摩擦系数为0.055～0.06,与光滑配副相比降低了30%左右,磨损率仅为光滑配副的1/3。在织构化钢盘表面进行双辉离子渗金属Cr、Mo,形成厚度为20～30μm的合金渗层,渗铬层表面Cr含量约为43.4%,生成Cr₂₃C₆等碳化物,硬度由HV250提高到HV1100左右;渗钼层表面Mo含量约为13.0%,含有Fe₃Mo₃C等碳化物,表面硬度高达HV800。在贫油润滑下,经过渗Cr/Mo处理,微孔化配副的摩擦系数由0.07降低到0.055,磨损率由8.1×10^-16m³（N*m）^-1下降到4.8×10¹⁶m³（N*m）^-1,干摩擦条件下,经过渗Cr/Mo处理,微孔化配副的摩擦系数由0.16下降到0.135,摩擦配副环的磨损率降低了50%以上。表面织构化和合金化结合,在贫油/干摩擦条件下,获得了较低的摩擦系数以及良好的耐磨性。ABAQUS有限元模拟结果表明,微孔的存在虽然在一定程度上减小了接触面积、增大了接触面的平均等效应力,但与光滑表面相比,明显减小了摩擦接触面前端和边缘区域的应力集中现象,使接触表面间应力均匀化,其中,微孔密度在8%～9%范围内的应力分布状态最佳,与摩擦磨损试验结果一致。利用弹流理论计算出润滑膜厚与粗糙峰的比值,通过Stribeck曲线判断不同速度和载荷下的润滑状态,由于织构化处理提高了流体润滑效应,摩擦配副可以在较低的速度下由混合/边界润滑过渡到流体润滑状态;结合磨损形貌分析,光滑表面的摩擦配副磨损状况加剧,而织构化表面的摩擦配副磨痕深度较浅,犁沟较少,微织构可以捕捉摩擦轨道上的磨屑,减小磨粒磨损;微织构可以作为润滑剂的存储器,延长了润滑膜的使用寿命。更多还原

【Abstract】 Friction and wear are the primary reasons of 80% invalidation in mechanical equipments, as a result of a huge economy loss, which not only waste energy and resource but also accelerate the equipments discarded and replaced. In this paper, mechanism of friction and wear reduction of laser surface texturing and behavior of contacted stress were analyzed, based on the effect of changing surface topography and structure on tribological properties, face seal system as the research target, friction and wear test and ABAQUS finite element simulation as the experimental flats. And the friction and wear discipline of laser texturing was also investigated. Experimental and theoretical basis of anti-wear technique of mechanical friction pairs can be provided in mechanical seal.Using a pulsed laser with a wavelength of 1064nm, the high-energy density pulsed laser were acted on frictional mates surfaces, forming the surface texturing structures of dimple/groove distributed equably, instructed with research achievements and literatures. Surface texturing with various dimensions, shapes and densities were generated in frictional material surfaces, by means of changing pulsed time, energy and interval. Vicker hardness between two dimples was measured to analyze the heat-affected function with laser induced. 3D topography was denoted with white-light intervene profile apparatus and the melt splashed status was observed by SEM. Simulating the face seal, friction and wear performance of texturing seal material mates PTFE/GCr15 were estimates. And the effect of various frictional mates and texturing parameters, such as diameter, depth, clearance, density and shape on tribological properties was also tested and the optimal texturing parameters can be acquired. Three-dimensional finite element simulations of sliding processing with ABAQUS software were adopted to analyze the equivalent stress with different diameters, clearances and densities.Then the alloying elements Cr, Mo were sputtered to the laser texturing steel surface by means of double glow plasma technology with the optimal technical parameters of 20mm pole interval, 800V source voltage, 880～900℃working temperature, 4h penetrating time and Ar as ambience. The intersection topography of alloying layer was observed by optical microscope, and the intersectional hardness was measured. Phases and organization were analyzed by XRD, and the ingredient of alloying layer was evaluated by SEM and EDS. The experimental results show that laser texturing can decrease the friction coefficient of PTFE ring/GCr15 disc from 0.1 to 0.075, and wear rate of mated texturing disc is 2/3 of the smooth disc with oil lubrication. After laser texturing, the PV value is increased from 6.5 MPa·m/s to 16.4 MPa·m/s and the maximal PV value can be improved by above 1.5 times. The oil film longevity is prolonged to 2 times.Compared with the tribological properties of two texturing with shape of groove and dimple, the friction coefficient of dimple-shape texturing sample is 0.065, lower than 0.08.of groove texturing sample, and the oil-storage ability of dimple is higher than the groove texturing sample. The wear rate of two texturing is about 10×10^-16m³/N*m, which is 2/3 of the smooth disc of 15.3×10^-16m³/N*m.For the dimple texturing mates, the friction coefficient and wear rate are decreased with diameter and depth increasing, and the oversized dimple will give a disadvantage to wear rate. With the dimple density increasing, the wear longevity is prolonged while the friction coefficient is decreased firstly then elevated. Combining various dimple parameters, it is concluded that the sample with dimples of 150μm in diameter, 500μm in clearance, 40μm in depth and 8.8% density has a optimal tribological performance, with the friction coefficient 0.055～0.06, and the wear rate is one third of the smooth sample’s.Then the alloying elements Cr, Mo were sputtered to the laser texturing steel surface by means of double glow plasma technology to form the hardened phases such as Cr₂₃C₆ and Fe₃Mo₃C, which can increase the pressed hardness and surface hardness from HV250 to above HV1100. The intersectional distribution of soft and hard phases in matrix may improve the wear-resistance ability. Cooperating effect of laser surface texturing and double glow plasma surface alloying technology on sliding surfaces, a lower friction coefficient and better wear-resistance can be achieved.The Cr and Mo alloying layer about 20～30μm is formed on texturing surfaces by means of double glow plasma technology. The Cr concentration is 43.4% with carbide phase Cr₂₃C₆ in Cr alloying layer, improving the hardness from HV250 to HV1100. And the Mo concentration is 13.0% with carbide phase Fe₃Mo₃C in Mo alloying layer with HV800.After Cr/Mo sputtering process, the friction coefficient of texturing mated is decreased from 0.07 to 0.055, and the wear rate is declined from 8.1×10^-16m³（N*m）^-1 to 4.8×10^-16m³（N*m）^-1 with oil lubrication. In dry friction, the friction coefficient of texturing and alloying frictional mates is decreased from 0.16 to 0.135, and the wear rate is declined to50%. Cooperating effect of laser surface texturing and double glow plasma surface alloying technology on sliding surfaces, a lower friction coefficient and better wear-resistance can be achieved.The finite element simulating results indicate that the dimples may decrease the contacted areas, increasing the average equivalent stress. It can be seen that the stress concentration in the front and edge on contacted surface is minimized, equalizing the whole stress and reducing the stress grads. The samples with about 8%～9% dimple density have the optimal stress distribution. The simulation results are consistent with the friction tests, validating the results of friction testing to some extents.The ratios of lubricating film and surface asperity of smooth and texturing friction mates are calculated with elasticity- hydrodynamics theory to estimate the lubricating states under various load and velocity with Stribeck Curve. The texturing sample may increase the ratios of lubricating film and surface asperity, transfer the lubricated region from boundary to hydrodynamic lubrication at lower speed in shorter time, compared with the smooth.Combining the worn surfaces morphologies, the wear track in texturing disc is shallower with less ploughs than the rigorous surface on smooth. The texturing can act as a lubricant reservoir and a trap for wear particles, both affording the contact surface lubricating fluid continuously and eliminating the plowing contribution to friction.更多还原