【作者】 何祥明；

【导师】 刘秀波；

【作者基本信息】 苏州大学 ， 机械制造及其自动化， 2012， 硕士

【摘要】 奥氏体不锈钢因其良好的力学性能和化学稳定性，在化工、机械、建筑、医疗等领域得到了广泛的应用。但受硬度低、耐磨性差等性能缺点的制约，其一般不能用作重要的摩擦运动副零部件。此外，很多在高温条件下承受强烈摩擦磨损作用的相对运动副零部件不仅要求具有优异的高温耐磨性与抗氧化性，而且由于高温条件下无法实现外加润滑而必须具有优异的高温自润滑性能。由于磨损基本发生于材料或零部件的表面，采用合适的表面工程手段在材料表面制备自润滑耐磨涂层无疑具有较高的经济性和可行性。激光熔覆技术对基体和涂层材料无限制，能实现在低熔点的工件上熔覆一层高熔点的合金，能控制稀释率，可局部熔覆，微观结构细致，热影响区小，并使涂层材料快速熔化和冷却而与基体材料形成良好的冶金结合，结合强度高。为了提高不锈钢的耐磨性并开发具有良好减摩耐磨性能的先进复合材料涂层新体系，本文分别以NiCr/Cr₃C₂、NiCr/Cr₃C₂-15WS₂-15CaF₂、NiCr/Cr₃C₂-15WS₂-30CaF₂合金粉末为原料，采用激光熔覆技术，在不锈钢表面制备自润滑耐磨复合涂层。利用SEM、XRD、EDS等手段分析了涂层的显微组织，利用显微硬度计测试了涂层的显微硬度，利用高温摩擦磨损试验机分别测试了涂层在不同温度（室温、300℃、600℃）及不同载荷（2N、5N、10N）下的干滑动磨损性能并分析了其磨损机理。结果表明：激光熔覆NiCr/Cr₃C₂合金粉末制备出了以γ-（Ni,Fe）镍基固溶体为基体、（Cr,Fe）₇C₃碳化物为增强相，厚度约0.8mm、组织致密均匀、与不锈钢基体呈冶金结合的耐磨涂层，其平均显微硬度约为850HV0.3；激光熔覆NiCr/Cr₃C₂-15WS₂-15CaF₂合金粉末制备出以γ-（Ni,Fe）为基体、（Cr,Fe）₇C₃/WC为增强相、WS₂和CrS为润滑相的自润滑耐磨涂层，涂层的厚度约0.6mm、组织致密均匀、与不锈钢基体形成良好的冶金结合，其平均显微硬度为620HV0.3；激光熔覆NiCr/Cr₃C₂-15WS₂-30CaF₂合金粉末制备出的涂层中的物相也为γ-（Ni,Fe）基体、碳化物增强相及硫化物润滑相，然而涂层的厚度仅为0.25mm。摩擦磨损测试表明，室温时，激光熔覆NiCr/Cr₃C₂耐磨涂层的摩擦系数和磨损率均最小，激光熔覆NiCr/Cr₃C₂-15WS₂-15CaF₂耐磨自润滑涂层的摩擦系数和磨损率稍大于NiCr/Cr₃C₂耐磨涂层，不锈钢基体的摩擦系数和磨损率最大；随着温度上升至300℃时，不锈钢基体和NiCr/Cr₃C₂耐磨涂层的磨损率增大，而由于润滑相被挤压至磨损表面发挥了润滑作用，激光熔覆NiCr/Cr₃C₂-15WS₂-15CaF₂自润滑耐磨涂层的磨损率减小，使得自润滑涂层在300℃拥有最小的摩擦系数和磨损率；当温度上升至600℃时，润滑相被氧化，失去了润滑效果，激光熔覆NiCr/Cr₃C₂耐磨涂层和NiCr/Cr₃C₂-15WS₂-15CaF₂自润滑涂层的磨损率大小接近。低载（2N）时，激光熔覆NiCr/Cr₃C₂-15WS₂-15CaF₂自润滑耐磨涂层中良好的强韧相结合赋予涂层良好的耐磨性能；中载（5N）时，除了强韧相结合为涂层提供有效抵抗磨损外，涂层中的润滑颗粒被挤压至磨损表面发挥了有效的减摩耐磨作用，使得涂层在中载时拥有更为优异的摩擦学性能；高载（10N）时，涂层中的润滑相发生脱粘大大减小了其润滑效果，硬质增强相发生剥离使得磨损表面产生凹坑、犁沟，涂层在高载时的磨损率变大。综合分析认为，激光熔覆NiCr/Cr₃C₂-15WS₂-15CaF₂自润滑耐磨复合涂层在中温（300℃）中载（5N）下具有优异的耐磨性能。更多还原

【Abstract】 Due to its good mechanical and high chemical stability, austenitic stainless steel findsextensive applications in mechanical, chemical, medical and architectural as well asnuclear engineering areas. But it can’t be used as key tribological moving componentsbecause of its relatively lower hardness and wear resistance. Moreover, there are manytribological components working in high temperature aggressive environments whereliquid lubricants and greases cannot be used, demanding combination of high-temperaturewear, oxidation and self-lubricating properties. Fabricating a self-lubricating wear-resistantcoating with advanced surface technology on a tribological component surface is one ofmost efficient and economic ways to solve the problem.Laser cladding is fundamentally a type of coating technology that utilizes a focused ora defocused high-power laser beam to locally melt the thin surface layer of a substrate andthe added materials while at the same time forming a new layer of material with desiredproperties after solidification. A great variety of powder materials or powder mixtures canbe effectively deposited onto the substrates to achieve various properties such as wearresistance and corrosion resistance. The microstructure of the deposited layer is very fineand has the typical characteristic of rapid solidification, so it can achieve completemetallurgical bond at the interface.In order to improve the wear resistance of austenitic stainless steel and develop newsystems of advanced composite coating with good wear resistance and anti-friction, theauthor individually used NiCr/Cr₃C₂, NiCr/Cr₃C₂-15WS₂-15CaF₂andNiCr/Cr₃C₂-15WS₂-30CaF₂alloy powder as raw materials, fabricated self-lubricatingwear-resistant coating on austenitic stainless steel by laser cladding. Microstructures of thecoatings were characterized by X-ray diffractometer （XRD）, scanning electron microscope（SEM） and energy dispersive spectrometer （EDS）. Microhardness of the coatings wasmeasured by a microhardness tester. The friction and wear properties of the coatings under different temperatures and loads were investigated, and the corresponding wearmechanisms were analyzed.The results showed that a wear resistant coating reinforced with hard （Cr,Fe）₇C₃carbide and toughened by ductile γ-（Ni,Fe） solid solution was fabricated by laser claddingusing NiCr/Cr₃C₂as precursor. The thickness and average microhardness of the coating isabout0.8mm and850HV0.3, respectively, and the bonding to the substrate is metallurgical.The microstructure is dense and uniform. A self-lubricating wear-resistant coatingconsisting of （Cr,Fe）₇C₃/WC, γ-（Ni,Fe）, WS₂and CrS were obtained usingNiCr/Cr₃C₂-15WS₂-15CaF₂as precursor. The thickness and average microhardness of theself-lubricating wear-resistant composite coating is about0.6mm and620HV0.3,respectively. When the precursor changes to NiCr/Cr₃C₂-15WS₂-30CaF₂, the thickness ofthe coating is only about0.25mm.At room temperature, NiCr/Cr₃C₂coating exhibits superior wear resistance. Frictioncoefficient and wear rate of NiCr/Cr₃C₂-15WS₂-15CaF₂coating are slightly higher thanNiCr/Cr₃C₂coating but far lower than stainless steel substrate. With the increase oftemperature, both the friction coefficients and wear rates of NiCr/Cr₃C₂composite coatingand stainless steel substrate gradually increased while that of NiCr/Cr₃C₂-15WS₂-15CaF₂coating decreased. The lubricant phase spreading out onto the worn surface at300℃wasbeneficial to the friction-reducing and wear-resisting. Whereas, the lubricant phasecouldn’t provide effective lubricious effect due to its oxidation at600℃and the wear ratesof NiCr/Cr₃C₂coating and NiCr/Cr₃C₂-15WS₂-15CaF₂coating were very close. Both thefriction coefficient and wear rate of NiCr/Cr₃C₂-15WS₂-15CaF₂coating firstly decreasedand then slightly increased with the increasing normal load.In conclusion, laser cladding NiCr/Cr₃C₂-15WS₂-15CaF₂self-lubricating compositecoating possesses excellent wear resistance and anti-friction under moderate temperature（300℃） andmoderate load （5N）.更多还原