【作者】 刘洪喜；

【导师】 汤宝寅；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2007， 博士

【摘要】 延长轴承疲劳寿命,尤其是滚动轴承的接触疲劳寿命一直是轴承工作者十分重视的研究课题。近几十年来,尽管钢材冶金质量、结构设计、加工制造、润滑技术等得到了较大改进,但轴承在实际工况下的疲劳寿命仍难以大幅度提高。本文从材料表面改性的角度出发,在总结热处理、物理气相沉积(PVD)、化学气相沉积(CVD)、离子注入等传统处理工艺的基础上,提出采用等离子体浸没离子注入与沉积(PIII&D)新技术,在GCr15轴承钢基体表面合成了TiN及其系列复合薄膜。测试结果显示,合成薄膜后轴承试样的滚动接触疲劳寿命得到了很大改善;不同参数下的Weibull分布曲线表明,处理后试样的疲劳寿命分散性明显减少。在分析合成薄膜后轴承钢试样疲劳寿命得以提高的因素中,阐明了试样表面结构、残余应力、薄膜类型、基体表面粗糙度、合成薄膜厚度等参数的影响。全面叙述了未经表面强化处理轴承滚动接触疲劳破坏的Lundberg.G和Palmgren.A最大动态剪切应力理论(L-P理论)及Weibull分布理论。指出了它们在分析PIII&D合成薄膜后轴承试样滚动接触疲劳破坏机理方面的局限和存在的不足。同时,以L-P理论和Weibull分布理论为基础,结合ANSYS有限元软件对接触循环应力应变场的模拟分析结果、Weibull分布曲线和薄膜试样疲劳破坏的扫描电镜原始形貌照片,提出了接触循环载荷作用下PIII&D合成TiN薄膜后轴承试样疲劳破坏的五阶段模型,分析得出其疲劳失效机理可能是膜层内部存在微观缺陷而产生细小裂纹,在循环载荷作用下裂纹不断扩展,同时受到剪切应力和润滑油中污染颗粒共同作用的结果。运用X光电子能谱(XPS)、X射线衍射(XRD)和原子力显微镜(AFM)分析了处理后试样表面的结构组成及表面状态。XRD图谱证实了薄膜中存在TiN相,并在(200)晶面表现出择优取向。距表面不同深度处Ti2p和N1s的XPS能谱泰勒分峰结果表明,表面膜层中主要存在钛的氮化物、氧化物和氮氧化合物,具体表现形式为TiN、TiO2、TiNxOy三种,同时也存在少许过量的单质氮。AFM表面二维、三维形貌及粗糙度曲线显示出表面薄膜结晶完整,结构致密,颗粒清晰可见。处理后轴承试样的纳米硬度和弹性模量较基体均有所增加,但不同工艺条件下增加的程度不同。其中最大纳米硬度和弹性模量较基体分别提高了127.3%和59.1%。纳米划痕曲线揭示出薄膜试样在整个划擦过程中先后经历了弹性变形、弹塑性变形、加载开裂和卸载剥离三个阶段,表明TiN薄膜具有较好的弹性恢复能力和与基体之间较强的结合力。采用掠入射X射线(GIXA)单峰法测试了不同膜厚下轴承钢试样表面的残余应力。结果表明,所有合成TiN薄膜的试样表面均存在较大残余压应力,且随着薄膜厚度的增加,膜层表面残余压应力值下降。摩擦系数曲线显示出合成薄膜后试样的摩擦磨损性能均优于基体材料,最低摩擦系数低于0.2。另外,处理前试样表面粗糙度愈低,合成薄膜后试样的机械性能相对愈好。ANSYS模拟分析结果显示:对于未经强化处理的滚动接触,一定轴向力作用下的最大Von mises应力出现在滚珠和轴承套环相接触的区域,并靠近边缘下方的拐角处,最大剪切应力发生在距离接触表面一定深度的地方。这种情形与L-P的最大动态剪切应力理论基本一致。对于合成TiN薄膜后的轴承,同样轴向力作用下的最大等效应力出现在膜基结合处。最大剪切应力出现在膜基界面,并位于薄膜内部。一定弹性模量下,最大等效应力和最大剪切应力均随着膜厚增加而逐渐变小。凭借自行研制的球棒疲劳磨损试验机测试了不同PIII&D工艺下轴承试样的滚动接触疲劳寿命。结合Weibull分布理论,运用C语言计算了薄膜试样的疲劳寿命特征参数,并绘制了相应的Weibull曲线。与基体相比,不同粗糙度和处理时间下,处理后轴承试样的滚动接触疲劳寿命明显延长。其中,TiN单层膜的最大L10提高了约9.2倍;L50提高了约4.2倍;La和平均寿命均分别提高了约3.5倍。疲劳寿命得以改善的原因与PIII&D合成薄膜后轴承试样表面粗糙度和摩擦系数的减小,表面组织和成份的优化及表面存在的压应力状态等有着密切关系。另外,复合薄膜的不同特征寿命均高于单层薄膜试样。处理后轴承试样疲劳破坏的光学显微及扫描电镜(SEM)原始形貌观察结果和疲劳破坏的五阶段模型揭示出PIII&D合成TiN薄膜后,轴承的疲劳失效机理是膜层内部存在微观缺陷而产生细小裂纹,在循环载荷作用下裂纹不断扩展,同时受到剪切应力和润滑油中污染颗粒共同作用的结果。更多还原

【Abstract】 To prolong the fatigue life, most of all, to extend the rolling contact fatigue life(FCF) of rolling bearing, is a very important research project for bearing staff at all times. In recent decades yeears, although the steels metallurgy quality, structure design, processing and lubrication technique made a great progress, it is difficult to increase to a great extent in practical operating condition. In the dessertation, from the point of view of the surface modification, based on the traditional processing of heat treatment, physical vapior desposition (PVD), chemical vapior desporation (CVD) and ion implantation, the plasma immersion ion implantation and deposition (PIII&D) technique is applied to synthesize titanium nitride (TiN) and a series of composite films on the GCr15 bearing steel substrate surface. It is shown that the RCF increased markedly, the fatigue life decentrality of treated samples decreased obviously according to the Weibull distribution curves. In order to analyse the RCF of treated sample, some effect facrors, such as surface micro-hardness, residual stress, substrate surface roughness, film types and film thickness are clarified. The maximum shear stress theory of Lundberg-Palmgren (L-P) and Weibull distribution theory of untreated bearing rolling contact fatigue destruction is depicted. The deficiency and limitation of these two theories in the field of rolling contact fatigue destruction mechanism after PIII&D was discussed. In addition to, based on the L-P theory and Weibull distribution theory, combined with the contact stress and strain field analysis results of ANSYS finite element software, Weibull distribution curves and fatigue destruction scanning electron microscope (SEM) photograph of film samples, the fatigue destruction five phase model of treated film bearing sample was educed.The phase compositions, surface quality and mechanical properties of TiN film bearing samples were be characterized by X-ray photoelcctron spectrum (XPS), X-ray diffraction (XRD) spectrium and atom force microscope (AFM). XRD spectra veried TiN phase exist in the film, and the (200) crystalline plane is the preferential orientation. The XPS analysis results of Ti2p and N1s in different surface depths show that TiN, TiO2 and TiNxOy exist in the surface film layer, and still a small quantity of remnant simple nitrogen. Two-dimensional and three-dimensional AFM morphology and roughness curves reveal that the surface film possess perfect crystalline, compact structure and clear grain.The nano-hardness and elastic modulus of TiN film bearing specimens are larger than that of GCr15 substrates’, but the extent vary with the processing. Compared with the GCr15 steel substrate, the maximal nano-hardness is 25GPa, increased by 127.3%; the maximal elastic modulus is 350GPa, increased by 59.1%. Nano-scratching curves display that the film bearing samples underwent three phases during the scratching: elastic deformation, elastic-plastic deformation, upload crack and no load delamination. It is also shown that TiN film has good elastic comeback ablity and a strong adhesion with the GCr15 bearing steel substrate.The surface residual stress of various TiN film thickness samples were be measured by grazing incidence X-ray analysis (GIXA). Analysis results revealed that all samples treated by PIII&D can produce residual compressive stress in the surface film layer, and the compressive stress value decrease with the TiN film thickness increse. Friction coefficient curves shown that the friction and wear behaviors of TiN film bearing samples is better than that of substrate’s, the minimal friction coefficient less than 0.2. In addition to, the lower of the substrate surface roughness before treated by PIII&D, the better of the mechanical property of TiN film bearing sample after PIII&D.ANSYS simulation results indicated that the maximal Von mises exist in the contact region of ball and bearing ring and colse up to the boundary corner for ordinary rolling conact under the axial force condition. The maximal shear stress generated in a certain depth under the surface. It is consistent with the maximum dynamic shear stress theory by Lundberg G. and Palmgren A.As far as TiN film bearing sample is concerned, under the identical axial force condition, the maximum Von mises generated in the film-substrate interface. The maximum shear stress initiated in the film-substrate interface, and point to the film interior. Film thickness has an important effect on the above-mentioned two kinds of stress. Under a constant film elastic modulus conditions, both the maximum Von mises and shear stress decreased with the film thickness increase. The author considered that maximal shear stress is still the main reason to induce the rolling contact fatigue failure of hard coating materials by PIII&D.The RCF life of TiN film bearing specimens tested using self-made ball-rod fatigue tester under different PIII&D processing conditions. Based on the fatigue life data and Weibull distribution theory, the different characteristic life parameters of film bearing samples were be done, and the Weibull distribution curves were be plotted.The RCF life of TiN and a series of composite film bearing specimen is prolonged under different substrate surface roughness and PIII&D implanted time conditions. All the characteristic fatigue life of TiN film bearing samples enhanced to a great extent. Thereinto, the maximum L10 , L50, La and average fatigue life of single layer TiN film bearing sample is about 9.2 times, 4.2 times, 3.5 times and 3.5 times larger than that of substrate’s, respectively. The reason, fatigue life improved after PIII&D, is that the enhancement of sample surface intensity and hardness; the descent of surface roughness and friction coefficient; the optimization of surface structure and chemical components and the state of surface compressive stress. According to the slope parameters of Weibull distribution curves, the characteristic fatigue life data of all composite film bearing samples are larger than that of single layer TiN film bearings.The optical microscope(OM) and SEM morphology of TiN film bearing specimen fatigue pitches shown that the micro-defects of film-substrate interface and close up to the film interior is the inducement to produce rolling contact fatigue pitches; the action of maximum shear stress together with the lubricant oil grain formed during the rolling cycle is the exterior driving force. The five phase model revealed that the rolling contact fatigue mechanism of PIII&D TiN film bearing is micro-defects in the film to lead to small cracks, and the cracks propagation gradually during the cycle load, with the help of lubrication oil grain combination with maximum shear stress; finally, the surface film was delaminated from the substrate.更多还原