【作者】 马宁；

【导师】 叶福兴；

【作者基本信息】 天津大学 ， 材料加工工程， 2014， 博士

【摘要】 重载、高磨损、冲击的恶劣工况，对工程机械零部件再制造表面涂层提出了更高的硬度和强韧性要求。因此，本文在分析工程机械轴类零件失效机制的基础上，提出“多尺度WC基金属陶瓷复合涂层”的材料设计思路，开发了一种具有高硬强韧的超音速火焰喷涂(HVOF)双峰结构WC-(nanoWC-Co)新涂层，成功应用于工程机械轴类零件的再制造。论文首先分析了装载机和平地机的拆解、清洗和检测方法，重点研究了其传动系统轴类零件的失效机制，发现磨粒磨损与接触疲劳是其失效的主要原因，并且发现废旧零件表层存在约50微米厚度的疲劳层。因此，首先要去除该疲劳层，再采用HVOF技术进行再制造。为获得高性能耐磨涂层，研究了工艺参数和粉末结构对HVOF制备WC涂层的影响。获得了优化的工艺参数：燃气（C3H8）气压0.65MPa，燃气流量30L/min，氧气气压0.7MPa，氧气流量245L/min，喷涂距离270mm。此外，设计了四种不同WC颗粒尺度（微米、亚微米、纳米和双峰结构）的WC-12Co粉末和一种WC-Co-Al粉末作为喂料，在优化工艺下研究了粉末结构对涂层组织性能的影响。结果表明：随着WC颗粒尺度减小，粉末沉积过程脱碳行为加剧，涂层的硬度提高，但韧性下降；WC-Co-Al粉末在喷涂过程中，Al元素氧化生成Al2O3相，既可以抑制WC脱碳也会改善涂层的力学性能。五种涂层中，纳米WC-12Co涂层硬度最高(1380HV0.1)，但表现出最低的断裂韧性(5.79MPa·m1/2)，双峰WC-(nanoWC-Co)涂层表现出最好的韧性10.76MPa·m1/2，并兼备优越的硬度1291HV0.1。纳米压痕试验研究表明，纳米WC颗粒的存在提高了双峰结构WC-(nanoWC-Co)涂层粘结相的硬度和弹性模量。对五种涂层的摩擦磨损行为研究表明，在与GCr15对磨环的干滑动磨损试验中，双峰涂层在所有涂层中表现出最优异的耐磨性。对磨损后形貌和磨屑分析发现，WC涂层主要磨损机制为粘结相被对磨环及磨屑犁削、粘着，表面疲劳引起WC颗粒的剥落与局部层离以及摩擦氧化膜的形成与剥离。最后将该WC-(nanoWC-Co)涂层成功应用于双排链轮轴等工程机械轴类零件的再制造。再制造涂层孔隙率低于1%，显微硬度为1256HV0.1，压痕断裂韧性达10.5MPa·m1/2，结合强度超过60MPa，干滑动摩擦条件下磨损失重不足GCr15轴承钢的1/20。通过建立废旧产品可再制造性评价的模型，评估了利用该方法修复双排链轮轴的再制造性，结果证明该再制造方法是完全可行的。更多还原

【Abstract】 Because of the severe working conditions such as heavy-load, high-abrasion andimpact, surface coating for remanufacture of construction machinery parts need ahigher hardness and toughness. Therefore, based on the analysis of failuremechanism of construction machinery shaft parts, a design idea of―multi-scale WCbased cermet composite coating‖was proposed, and a new high velocity oxy-fuel(HVOF) sprayed bimodal WC-(nanoWC-Co) coating of high hardness, strength andtoughness was developed and successfully applied in remanufacturing of shaft partsin construction machinery.Firstly, we analyzed dismantling, cleaning and testing methods of grader andloader, especially focused on the failure mechanism of transmission shaft parts, andfound that abrasive wear and contact fatigue were the main reasons for the failure ofthe parts. Furthermore, a surface fatigue layer with thickness of~50microns wasfound in scrap parts. Consequently, this fatigue layer has to be removed before thescrap parts are remanufactured by HVOF technique. In order to obtain high-qualitywear-resistant coating, effects of process parameters and powder structure on thepreparation of HVOF-sprayed WC-12Co coating were investigated. The optimizedprocess parameters were obtained which were propane gas pressure of0.65MPa,propane flow rate of30L/min, oxygen pressure of0.7MPa, oxygen flow of245L/min and spraying distance of270mm. Furthermore, four kinds of WC-12Copowders with different WC particle size (micron, submicron, bimodal and nanometer)and one kind of WC-Co-Al were designed as feedstock used to study the influence ofpowder structure on the properties of coatings sprayed under the optimizing HOVFparameters. The results showed that decarburization behavior of WC particlesaggravated during deposition process with the decrease of the WC particle size, andthe corresponding coating hardness increased, but the toughness decreased. Duringspraying Al reacted with oxygen and Al2O3phase was generated, which inhibited thedecarburization of WC and improved the mechanical properties of the coatings.Nanostructured WC-12Co coating showed the highest hardness (1380HV0.1) in thefive kinds of coating, but the worst fracture toughness (5.79MPa·m1/2), bimodalWC-(nanoWC-Co) coatings shows the best toughness which was10.76MPa·m1/2,and also a superior hardness of1291HV0.1. The results of nanoindentation test showed that the existence of nanometer WC particles increased the hardness andelastic modulus of the matrix in bimodal WC-(nanoWC-Co) coatings. Study on thefriction and wear behavior of five kinds of WC coatings showed that bimodalWC-(nanoWC-Co) coatings exhibited the most excellent wear esistance in the fivekinds of coatingswhen dry sliding against a GCr15ring. Through analysis of wearmorphology and wear debris, the main wear mechanism of WC coatings was found.That was adhesion and micro-cutting of the binder phase by GCr15ring and weardebris, spalling of WC particles and local delamination caused by fatigue crackpropagation, and accompanied by the formation and detachment of oxide film.Finally, this bimodal WC-(nanoWC-Co) coating has been successfully applied onremanufacturing of construction machinery shaft parts such as double row sprocketshaft. The remanufacturing coating had a compact microstructure with the porositylower than1%and excellent mechanical properties with a microhardness of1256HV0.1, the indentation fracture toughness of10.5MPa·m1/2, bonding strength morethan60MPa and wear mass loss less than1/20of GCr15bearing steel under thecondition of dry sliding wear. Through the establishment of evaluation model ofwaste product remanufacturing, the re-manufacturability of double row sprocketshaft remanufactured by this method was evaluated and the result was very satisfied.更多还原