【作者】 赫庆坤；

【导师】 王勇；

【作者基本信息】 中国石油大学 ， 化工过程机械， 2009， 博士

【摘要】 随着国内油田大部分进入高含水开发期,由于高含砂、高含水、高矿化度、高温蒸汽稠油开采、注聚合物开采及强腐蚀介质等因素的影响,抽油泵腐蚀磨损日趋严重,严重影响着油田开发。本文利用激光熔覆原位合成技术在抽油泵柱塞表面成功制备出TiC/NiCrBSi熔覆层,对熔覆层的微观组织、耐磨性、耐蚀性以及TiC与金属基体的界面性能进行了系统分析,研究了影响熔覆层组织和性能的主要因素。抽油泵柱塞表面失效的原因是多方面的。砂粒在抽油泵内的沉降,导致柱塞的划伤;高压差下含砂液体的水力切割;泵挂的加深,使柱塞与泵筒之间的摩擦力增大;非竖直的井身结构,加重柱塞和泵筒之间的局部腐蚀磨损;井下高温加剧了柱塞和泵筒腐蚀和结垢。柱塞表面的失效形式为磨粒磨损、腐蚀磨损、粘着磨损和腐蚀。其中磨粒磨损主要包括凿削磨损、冲刷磨损、碾磨磨损、划伤磨损和喷射磨损;腐蚀主要包括电偶腐蚀、均匀腐蚀和疲劳腐蚀。柱塞表面的失效以腐蚀磨粒磨损为主。分别向Ni35或Ni60中加入Ti粉和石墨粉,利用激光熔覆原位合成了TiC颗粒增强的NiCrBSi熔覆层,熔覆层与基体形成良好的冶金结合。从熔覆层的底部到顶部,TiC颗粒的体积分数依次升高;颗粒尺寸从纳米级逐步增大至微米级。熔覆层的硬度沿熔深方向由表及里呈下降趋势。TiC/Ni60熔覆层硬度明显高于TiC/Ni35熔覆层,TiC与(Fe,Ni)固溶体的结合界面洁净,无反应物和附着物,两相间共格性和相容性优良,TiC颗粒中存在大量位错,呈一定的方向分布。熔覆工艺是影响激光熔覆原位合成TiC/NiCrBSi熔覆层组织和性能的重要因素。研究表明,当预熔覆层厚度为1mm,扫描速度为150mm/min,激光扫描功率为3500W时,可获得表面平整,成型较好,稀释率较低,硬度较高的熔覆层。三层熔覆能有效降低母材金属对熔覆层的稀释率,增加熔覆层中TiC增强相的数量和尺寸,获得花瓣状和颗粒状的TiC,有利于获得硬度高而均匀的熔覆层。激光合成TiC/NiCrBSi熔覆层裂纹主要是由M23C6引起的熔覆层低塑性及残余内应力导致的脆性冷裂纹。通过减少粉末中的石墨含量进而降低熔覆层的含碳量,可以改善熔覆层组织,提高塑韧性,降低残余内应力,从而降低裂纹敏感性。对于熔覆层组织中陶瓷相偏聚的问题,通过向熔覆层中添加适量的Mo,使陶瓷相的偏聚现象明显减轻甚至消失。Mo可以改善TiC对NiCrBSi基体的界面润湿性,使TiC颗粒弥散分布于NiCrBSi固溶体中,有助于阻碍原位合成过程中TiC晶粒的聚集长大,从而细化TiC晶粒,改善熔覆层组织的均匀性,提高熔覆层硬度和耐磨性,降低摩擦系数。但添加过量的Mo,熔覆层硬度和耐磨性下降。向熔覆层中加入适量的稀土,可以改善熔覆层的耐磨耐蚀性。镧与熔池中的微量杂质形成组分复杂的微小化合物,作为非自发形核质点,对TiC和基体金属起到增加形核核心,细化晶粒和净化熔覆层组织的作用,提高了熔覆层的硬度和耐磨性,同时LaF3提高了熔覆层的电极电位,降低了腐蚀电流,改善了熔覆层的耐蚀性能。磨损试验表明,三层熔覆能够更好的发挥出TiC颗粒的增强作用,具有优良的耐磨损性能。TiC/Ni基熔覆层表层由于耐磨硬质点的存在,阻碍了磨痕的发展,其阻碍和钉扎行为在摩擦过程中发挥了强烈的阻磨作用,使熔覆层的磨损量大大降低。熔覆层基体的磨损机制主要是显微切削与粘着磨损。TiC/Ni基熔覆层耐磨性优于Ni60熔覆层。TiC/Ni基熔覆层与Ni60熔覆层相比较,前者具有较高的电极电位,后者具有较小的腐蚀电流;TiC/Ni基熔覆层能够提高碳钢基体的耐蚀性,其耐均匀腐蚀性劣于Ni60熔覆层,但耐局部腐蚀性能优于Ni60熔覆层。在腐蚀磨损试验中,TiC/Ni基熔覆层中的TiC颗粒发挥着增强和阻磨作用;腐蚀优先在晶界或相界处发生,削弱了TiC颗粒与基体的结合力,TiC颗粒在磨损作用下发生少量脱落,因此腐蚀加剧了磨损。腐蚀磨损形貌为切削犁沟和腐蚀坑。腐蚀磨损机制为腐蚀磨粒磨损。TiC/Ni基熔覆层的腐蚀磨损性能优于Ni60熔覆层,原因在于此工况条件下的腐蚀磨损以磨损为主,腐蚀为辅。更多还原

【Abstract】 With most of the domestic oil field entering the high watery development period,corrosive wear of oil well pump is increasingly serious due to the effect of high content of sand,water and salinity,high temperature steam heavy oil mining,polymer injection and strong corrosion medium,which seriously affects the exploitation of oil fields.In this research,the Ni-based cladding layer reinforced by in-situ fabricated TiC by laser cladding on the surface of oil well pump plunger.The microstructure、wear and corrosion properties of the cladding layer were analyzed systematically as well as the interfacial properties between TiC and metal substrate and the main factors influencing microstructure and properties.The reasons of failure on the surface of oil pump plunger are various.Sand deposition in the pump will lead to the scratch of the surface of plunger; the liquid with sand under high pressure difference will cause the incising; the increased pump setting depth will result in the increase of friction force between the pump barrel and the plunger; the local corrosion and wear between the pump barrel and the plunger is more serious due to the non-vertical structure of the well; high temperature underground aggravates the corrosion and scaling of the pump barrel and the plunger.The failure mechanism of the plunger surface is abrasive wear,corrosion wear,sticking and corrosion.Abrasive wear mainly includes gouging abrasive wear,erosion wear,grinding wear and tear,scratches wear and jet wear.Corrosion mainly includes galvanic corrosion,uniform corrosion and fatigue corrosion.The main failure of the plunger surface is corrosion and abrasive wear.Through adding Ti and graphite powder to Ni35 or Ni60,the Ni-based cladding layer reinforced by in-situ TiC was prepared by laser cladding. The cladding layers have an excellent metallurgical bonding with the substrate.The volume fraction of TiC particles increases successively from the bottom to the top of the cladding layers,and the particle size changes gradually from the nanometer to micron level.The hardness of the cladding layer decreases from surface to substrate of the cladding layers,and the hardness of the TiC/Ni60-based cladding layer is much higher than that of TiC/Ni35.The bonding interface between TiC phase and the solid solution(Fe,Ni) is clean without reactants and attachments,and the coherency and compatibility of these two phases is excellent.There is a great deal of dislocation in TiC particles,which distributes in some direction.The laser cladding technology is also the important factor influencing the microstructure and properties of the Ni-based TiC composite cladding layer. The results show that the cladding layer with good appearance,low dilution rate and high hardness could be obtained when the thickness of the pre-coated powder is 1mm,scanning speed is 150mm/min and cladding power is 3500W. The laser cladding with three layers can effectively reduce the dilution rate of base metal to the cladding layers,increase the quantity and size of the TiC reinforcement in cladding layer,and get petal-shaped and granular TiC particles,which are beneficial to get the uniform cladding layer with high hardness.Cracks in TiC/NiCrBSi cladding layers are mainly cold brittle cracks resulted from low ductility of the cladding layer due to the existence of M23C6 phase and residual internal stress.Through decreasing the carbon content of the cladding layers by means of reducing the graphite content of the powder,the microstructures of the cladding layers can be improved,plasticity and toughness can be enhanced,and residual stress can be decreased,therefore,the cracking susceptibility can be reduced.As for the ceramic phase segregation in the microstructure of the cladding layer,this phenomenon can be obviously lightened and even disappear by adding Mo to the cladding layer.Mo can improve the interfacial wettability of TiC phase to Ni-base phase,which makes TiC particles dispersedly distribute in the Ni-based solid solution phase.This contributes to impeding the accumulation and growth of TiC during the process of in-situ fabrication,improving uniformity,rigidity,wear resistance,refining TiC grains,reducing friction coefficient.However,the hardness and wear resistance of cladding layer decrease with the addition of excessive Mo.The corrosion and wear resistance of cladding layer can be improved through adding appropriate content rare earth to the cladding layer. La and trace of impurities in the molten pool form the tiny compounds with complicated components,which can be considered as non-spontaneous nucleation particles.These particles contribute to increasing nucleation cores,refining grains and cleaning the structure of the cladding layers,and increase the hardness and wear resistance can be improved.Meanwhile electrode potential can be improved while corrosion current can be reduced by LaF3,The corrosion resistance of cladding layer can be improved.Wear test indicates that three-layer claddings make reinforcement performance of TiC particles more effective and have excellent wear resistance property. Wear-resistant hard particles on the surface of TiC/NiCrBSi cladding layers hinder the extension of the wear scar,and the hindering and pinning action prevent the wear seriously,so that the wear loss of TiC/NiCrBSi cladding layers decreases remarkably.The main wear mechanism of cladding layers matrix is microdissection and adhesive wear.Wear resistance of TiC/NiCrBSi cladding layers is better than that of Ni60 cladding layers with the reason of the former’s lower friction coefficient.Compared with Ni60 cladding layers,TiC/NiCrBSi cladding layers have higher electrode potential,but higher corrosion current.TiC/NiCrBSi cladding layers can improve the corrosion resistance of the carbon steel matrix,and have lower uniform corrosion resistance and higher local corrosion resistance than Ni60 cladding layers.During the experiment of corrosion wear,TiC particles in TiC/NiCrBSi cladding layers play the roles of enhancement and frictional resistance.Corrosion happens preferentially on grain or phase boundaries,and weakens the adhesive force between TiC particles and the matrix.As a result,corrosion aggravates the wear and TiC particles fall off more easily due to the wearing action.Corrosion wear morphology is cutting plough ditch and etch pits.The mechanism of corrosion wear is corrosion abrasive particle wear.It is because wear predominates over corrosion under this working condition that corrosion wear property of TiC/NiCrBSi cladding layers is better than that of Ni60 cladding layers.更多还原