摘要
在航空、航天、核能、军工等尖端技术领域，存在着大量在高真空度、高温、高速、重载等苛刻工况环境下运行的摩擦运动副零部件，如高温绝热发动机轴承、活塞环、缸套、核阀、汽轮机叶片等，普通的润滑油脂已不能完全满足使用要求，固体自润滑涂层是解决上述问题的有效途径之一，而激光熔覆技术是一种先进的、具有远大前景的表面改性技术。
本文分别以NiCr/Cr_3C_2、NiCr/Cr_3C_2-30%WS_2、NiCr/Cr_3C_2-30%WS_2包覆和NiCr/Cr_3C_2-15%WS_2包覆合金粉末为原料，采用激光熔覆技术在0Cr18Ni9奥氏体不锈钢基体表面制得高温耐磨自润滑复合材料涂层。采用XRD、SEM和EDS等现代材料分析手段深入研究了各涂层的显微组织及物相组成。采用HT-1000型高温摩擦磨损试验机测试了各种复合材料涂层在室温/高温下的干滑动摩擦学性能，并分析了其磨损机理。
激光熔覆NiCr/Cr_3C_2涂层的显微组织由Cr_7C_3增强相及γ/Cr_7C_3共晶基体构成；而添加30%WS_2的涂层除上述物相外，还存在大量(Cr, W)C复合碳化物及少量CrS、WS_2固体润滑颗粒。对WS_2进行化学镀包覆，有效抑制了固体润滑剂WS_2在激光辐照下的分解，使添加30%WS_2包覆涂层中(Cr, W)C相明显减少、WS_2含量提高。
高温磨损试验表面：各涂层的摩擦系数随温度的升高而降低，而磨损率随温度的升高而增大。在所有涂层中，激光熔覆NiCr/Cr_3C_2-30%WS_2包覆涂层在各温度下具有最低的摩擦系数与磨损率，表现出良好的耐磨减摩性能，其自润滑性能源于WS_2和CrS的固体润滑作用。
本项目的研究，丰富和扩展了金属基高温耐磨自润滑复合涂层的组成体系，对其激光熔覆加工工艺提供有价值的研究方法和试验基础，为满足现代工业中关键高温运动零部件更高服役性能的需求进行有益的尝试。
Solid self-lubricating coatings are primarily used to control friction and wear undersevere application conditions, such as high vacuum, high speeds, high loads, and very hightemperatures in aviation, aerospace, nuclear energy, military and other cutting-edgetechnical fields (the High-temperature adiabatic engine bearings, piston rings, cylinderliner, nuclear valves, turbine blades, etc.), where conventional materials and lubricantscannot provide the desired performance or durability. In addition the laser cladding is anadvanced surface modification technology with great prospects.
In this paper, the NiCr/Cr_3C_2, NiCr/Cr_3C_2-30%WS_2, NiCr/Cr_3C_2-30%WS_2encapsulating and NiCr/Cr_3C_2-15%WS_2encapsulating are used as alloy powders preplacedon the0Cr18Ni9austenitic stainless steels, then the high-temperature wear-resistantself-lubricating composite coatings are fabricated by laser cladding technology. Phaseconstituents and microstructures were deeply investigated by X-ray diffractometer (XRD),scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Thetribological properties of the fabricated composite coatings were evaluated using aball-on-disc wear tester (HT-1000tester, Lanzhou Zhongkekaihua) under dry slidingcondition at room-temperature,300℃and600℃, respectively, and the wearmechanisms were also discussed.
Results show that the phase constituents of NiCr/Cr_3C_2coating are composed of Cr_7C_3reinforcement phase and matrix of γ/Cr_7C_3eutectic. However, the coating added with WS_2also has a large number of (Cr, W) C hybrid carbides and a small amount of WS_2, CrSlubricants apart from the above phases. When the WS_2are encapsulated by electrolessplating, it can effectively inhibit the decomposition of solid lubricant WS_2during lasercladding, therefore, the (Cr, W) C phase decreased significantly and WS_2content increasedin the coating added with WS_2encapsulating powder.
The high-temperature wear test show that friction coefficients of above coatings bothdecrease with increasing temperature, but the wear rates both increase. At all testtemperatures, the coating added with30%WS_2encapsulating powder has the lowestfriction coefficient and wear rate. Its superior friction-reducing and wear-resistanceproperties are owing to the presence of WS_2and CrS lubricants.
This research expanded the material system of the metal-based high-temperaturewear-resistant self-lubricating composite coating, provided valuable research methods andexperimental basis on the laser cladding process, and made a useful attempt to meet thehigher service performance of key high-temperature moving parts in the fields of modernindustrial.
引文
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