退火温度对DLC和Si-DLC涂层微观结构和摩擦学性能的影响

Effect of Annealing Temperature on Microstructure and Tribological Properties of DLC and Si-DLC Coatings

类金刚石(DLC)涂层因具有优异的减磨耐摩性能被广泛应用,而涂层内部存在较高的内应力这一缺点限制其在摩擦学领域的进一步应用。退火处理可以通过改变涂层微观结构来降低涂层内应力,从而提高涂层的摩擦学性能。为研究退火温度对DLC和硅掺杂类金刚石(Si-DLC)涂层微观结构和摩擦学性能的影响,采用等离子体增强化学气相沉积(PECVD)和电弧离子镀的复合沉积技术制备DLC和Si-DLC涂层,将涂层在大气环境中进行不同温度的退火处理。运用扫描电子显微镜、高分辨率透射电子显微镜、拉曼光谱以及XPS光谱仪对涂层摩擦试验前后的形貌和结构进行表征,采用纳米压痕仪和摩擦磨损试验机测试涂层的力学性能和摩擦学性能。结果表明:沉积的DLC和Si-DLC涂层为非晶结构。退火温度对涂层的微观结构和摩擦学性能有重要影响。随着退火温度从RT上升到500℃,由于C-H键断裂,C网发生集束化,DLC涂层的sp^(3)含量呈现先上升后降低的趋势,涂层的sp^(3)含量在300℃热处理后获得最大值,涂层硬度达到最大的20.66 GPa;而Si-DLC涂层由于Si元素的掺杂提高了涂层的热稳定性,其在400℃热处理时sp^(3)含量最大,硬度最大值为24.28 GPa。涂层与氧化锆对磨球的磨损机理为磨粒磨损,涂层的磨损率呈现先降低后升高的趋势,热处理温度为300和400℃为最优。研究证明涂层的微观结构和摩擦学性能可以通过热处理温度调控,优选热处理温度的涂层具有优异的综合性能。研究结果可为退火处理对DLC和Si-DLC涂层的性能影响提供理论支持。

Diamond-like carbon(DLC)coatings have excellent tribological properties,high chemical stability,and corrosion resistance,and they are often used as solid lubricants in the industrial field.However,the service lives of DLC coatings are shortened by their shortcomings of low thermal stability and high internal stress.Currently,defects in DLC coatings can be optimized via element doping,multilayer film design,and heat treatment.The carbon bond structure inside DLC coatings can be changed by Si doping,which reduces the internal stress of the coatings.Annealing treatments not only maintain the structural characteristics of the coating but also release its internal stress.However,the structure of the coating is destroyed when the annealing temperature is high.To study the effect of annealing temperature on the microstructure and tribological properties of DLC and Si-DLC coatings,DLC and Si-DLC coatings were prepared via plasma enhanced chemical vapor deposition and arc ion plating.The coating was composed of a surface layer and a CrN transition layer.The Cr element came from the Cr target,the Si element of the Si-DLC coatings was derived from tetramethylsilane,and the C element was derived from acetylene gas.Then,the coatings were placed in a muffle furnace and annealed at 200,300,400 and 500℃,and the annealed coatings were tested.The microstructure,mechanical properties,and tribological properties of the coatings at different annealing temperatures were studied to analyze the relationships between them and their annealing temperatures.The morphologies and structures of the coatings were characterized via scanning electron microscopy,high-resolution transmission electron microscopy,Raman spectroscopy,and X-ray photoelectron spectroscopy.The mechanical and tribological properties of the coatings were tested using nanoindentation and friction and wear testing machine.The results showed that the coatings had both transition layer and surface layer structures and that the coating surface was smooth and dense.Both DLC and Si-DLC coatings had amorphous structures.The annealing temperature had an important effect on the microstructure and tribological properties of the coatings.With the increase of annealing temperature from room temperature to 500℃,owing to the fracture of the C-H bond and the clustering of the C network,the sp3 content of the coating first increased and then decreased.After annealing at 200℃,the structure and mechanical properties of DLC and Si-DLC coatings did not change significantly.The coating structure was changed by the precipitation of H atoms.The DLC coating heat-treated at 300℃achieved the maximum sp3 content,and the hardness of the DLC coating reached a maximum value of 20.66 GPa.The sp3 content of the Si-DLC coating was the largest at 400℃,and the maximum hardness of the Si-DLC coating was 24.28 GPa.The thermal stability of the Si-DLC coating was improved due to the doping of the Si element.When the temperature exceeded 400℃,the coatings failed.After annealing at 500℃,the ID/IG value of the DLC and Si-DLC coatings increased,and the coatings were graphitized,which resulted in a sudden drop in the mechanical properties of the coatings.The tribological test results showed that the wear mechanism of the coatings against the ZrO2 ball was abrasive wear.The wear rate of the coatings was related to the mechanical properties,showing the trend of first decreasing and then increasing.The optimal heat treatment temperatures of DLC and Si-DLC coatings were 300 and 400℃,respectively.In summary,the microstructure and tribological properties of the coating can be controlled by the heat treatment temperature,and the coatings have excellent comprehensive properties at the optimal heat treatment temperature.The results of this study provide theoretical support for the effect of annealing treatments on the properties of DLC and Si-DLC coatings,and have theoretical and practical value for the application of heat treatments to DLC coatings.