【作者】 郭华锋；

【导师】 黄因慧；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2018， 博士

【摘要】 Ti6Al4V钛合金具有低密度、高比强度和良好的耐腐蚀性等优点,在航空航天、石油化工及民用领域应用非常广泛。其耐磨性差已成为国内外学者研究的热点,表面涂层技术是提升钛合金表面耐磨性的有效途径。常规涂层依然存在高孔隙、多裂纹等问题,如何制备高质量耐磨涂层并实现质量可控仍需进一步深入研究。以钛合金基体为研究对象,遵循粒子加速-飞行-加热-撞击-扁平化-冷却凝固-形成涂层的规律,采用理论分析、数值模拟和试验相结合的研究思路,基于超音速火焰喷涂技术成功制备微米和微纳米结构WC-12Co涂层,分析两种涂层的微观组织和性能。建立工艺参数和涂层质量间的多元回归数学模型,优化涂层质量。采用激光重熔技术实现涂层基体间界面行为的转变。主要工作和成果如下:(1)在分析粒子动量传输特征的基础上,建立飞行粒子加热熔化有限元模型。定量研究并揭示粉末粒径、飞行速度和喷涂距离等对熔化模式演变的影响规律,从而建立WC-12Co粉末的颗粒熔化机制理论模型。(2)计算WC-12Co颗粒的时空独立性,掌握撞击及扁平化行为,研究WC颗粒的反弹机理。建立涂层残余应力计算模型,为揭示材料和工艺因素对其贡献大小提供理论依据。明确涂层以机械结合为主的界面状态。表征涂层原生性微观缺陷的不均性,定量研究孔隙的尺寸类型和分布。(3)研究两种涂层的微观形貌及摩擦学特性等。讨论材料特性和工艺参数对微观组织及性能的影响,分析涂层及基体的磨损机理。微纳米涂层以亚微米、纳米尺度WC颗粒为主,微米涂层以微米、亚微米尺寸为主。微纳米涂层的孔隙率和摩擦因数相对较小,硬度和抗变形能力优于微米涂层。基体以磨粒磨损,黏着磨损和少量氧化磨损为主要磨损机制。微米涂层以微切削和剥层为主,而微纳米涂层主要以微切削为主。两种涂层都表现出优异的耐磨性,其中微纳米涂层更优。(4)揭示残余应力对粉末特性和动量传输特征的依赖性。明确涂层中残余压应力的产生主要由未熔化的WC颗粒的喷丸效应引起,与喷涂工艺无关。(5)建立喷涂工艺参数与涂层质量间的多元回归数学模型,验证模型的可靠性和精度,预测和优化了涂层质量。制备了高质量WC-12Co涂层,提升了涂层质量的可控性。(6)建立Marangoni效应多物理耦合场模型,揭示激光熔池的对流传热本质和涂层成分均匀化的驱动力来源。建立激光重熔热喷涂涂层的三维温度场有限元模型,分析工艺参数对熔池温度场演变的影响规律。选择优化工艺参数成功制备无孔隙和冶金结合的激光重熔涂层。探索出获得高质量激光重熔WC-12Co涂层的技术路线。更多还原

【Abstract】 Ti6Al4V titanium alloy has the advantages of low density,high ratio strength and good corrosion resistance.It is widely used in aerospace,petrochemical and civil fields.The poor wear resistance has become a research focus for scholars at home and abroad.Surface coating technology is an effective way to improve the tribological properties of titanium alloy surface.It is necessary to further study how to prepare high quality wear resistant coatings and achieve quality control.In this paper,using the titanium alloy substrate as the research object and follow particle acceleration-flight-heating-impact-flattening-cooling solidification-forming coating rules.Based on theoretical analysis,numerical simulation and experimental research,the micron structure and micro/nano structure WC-12 Co coating were successfully prepared by high velocity oxygen fuel technology.The microstructure and properties of the two coatings were analyzed.The multiple regression mathematical model of process parameters and coating quality was established,and the coating quality was optimized.Finally,laser remelting technology was used to realize the change of interface behavior between the coating and substrate.The main work and results of this paper are as follows:(1)On the basis of analyzing the characteristics of particle momentum transfer,a finite element model was established and the effect of powder particle size,flight speed and spray distance on the evolution of melting model were studied quantitatively.The theoretical model of particle melting mechanism of WC-12 Co powder was established.(2)The spatio-temporal independence of WC-12 Co powder particles was calculated,and the impact and flattening behavior of WC-12 Co particles were obtained.The rebound mechanism of WC particles was revealed.The calculation model of residual stress in coating was established which provided the basis for revealing the material and technological factors for its contribution.The interface state between coating and substrate with mechanical combination was clarified.The heterogeneity of the microstructure in coating was characterized and the size type and distribution of pore were studied quantitatively.(3)The microstructure and tribological properties of the two coatings were compared and analyzed.The influences rule of material properties and spraying process parameters on microstructure and properties of coatings were discussed.The wear mechanism of coating and substrate was revealed.Micro/nano coatings are mainly composed of submicron and nano-scale WC particles.Micron coating is mainly micron and submicron size.The porosity and friction coefficient of micronano coatings are relatively small,and the hardness and anti-deformation capability are better than micron coating.The wear mechanism of the substrate and the coating is obviously different.The Ti6Al4 V substrate shows the comprehensive wear mechanism with abrasive wear,adhesion wear as the dominant and oxidation wear as the auxiliary.Micron WC-12 Co coating is characterized by the abrasive wear mechanism of micro-cutting and peeling,while micro/nano WC-12 Co mainly adopts the abrasive wear mechanism of micro-cutting.Both of the coatings show excellent wear resistance and the micro/nano coating is more advantageous.(4)The dependence of residual stress on powder characteristics and momentum transfer characteristics is revealed.It is clear that the residual compressive stress in the coating is caused by the blast effect of the unmelted WC particles which is not related to the spraying process.(5)Based on statistical theory,a multivariate regression mathematical model of technological parameters and coating quality was established.The reliability and precision of the model were verified by the supplementary test.The prediction and optimization of coating quality are realized.The high quality WC-12 Co coating was prepared,which improved the quality controllability of coating.(6)The Marangoni effect multi-physical coupling field model was established.It is revealed that the convective heat transfer nature of laser molten pool and the driving force of the homogenization of coating components.The 3D finite element model of temperature field of laser remelting thermal spraying coating was established,and the influence of technological parameters on the evolution of molten pool temperature field was analyzed.A non-porous and metallurgical bonded laser remelting coating was successfully prepared by optimized process parameters.The technical route of high quality laser remelting WC-12 Co coating was developed.更多还原