C_(2)H_(2)流量对反应溅射石墨制备非晶碳膜层结构及性能影响研究

Effects of C_(2)H_(2)Flow Rate on Structure and Properties of Amorphous Carbon Films Prepared by Reactive Sputtering Graphite

目的研究反应溅射石墨制备非晶碳过程中乙炔流量变化对非晶碳微观结构、力学性能及摩擦学性能的影响规律。方法通过在乙炔气氛中反应溅射石墨靶,调控乙炔流量,制备不同结构的非晶碳膜层,采用X射线光电子能谱仪、激光共聚焦拉曼光谱仪分析膜层的微观结构,采用纳米压痕仪表征膜层的力学性能,采用球盘式摩擦磨损试验机、白光干涉仪和光学显微镜表征膜层摩擦学性能。结果通过反应溅射法制备了致密均匀的非晶碳,分析发现,所有薄膜表层均含有一定量O元素(原子数分数为6.36%~13.86%)。经Ar^(+)刻蚀后,大部分膜层的O含量可降至1%以下;随着乙炔流量的增加,膜层的硬度(H)、弹性模量(E)和H^(3)/E^(2)均呈先增后减的趋势,在乙炔流量为10 cm^(3)/min时膜层的硬度和弹性模量达到最大值,分别为27.93、233.55 GPa;摩擦学性能测试结果显示,膜层的平均摩擦因数在0.09~0.11之间,在启动阶段摩擦因数随着氢元素(H)含量的增加呈下降趋势,5 cm^(3)/min试样的膜层的耐磨性最高、磨损量最小,其磨损量为0.72×10^(−16)m^(3)/(N·m)。结论通过调节反应溅射石墨过程中乙炔的流量,可调控非晶碳中sp^(3)/sp^(2)、H含量,进而达到调控非晶碳力学性能、摩擦学性能的目的。

Amorphous carbon film,which combines good chemical inertia,wear resistance and mechanical properties,has been applied in aerospace,automotive,magnetic storage,mechanical processing and other fields.sp^(3) ratio and H content significantly influence microstructure and tribological properties of amorphous carbon.Especially,the tribological behavior of amorphous carbon with different sp^(3) ratio and H content varies greatly in the run-in stage under vacuum and air,which means a lot for wear pair design in aerospace equipment components.This work aims to investigate the relationship between film structure and properties,so as to find the optimum processing window.Mirror-polished 9Cr18 pieces(diameter 35 mm×thickness 3 mm)were used as substrates to deposit films by means of pulsed DC reactive sputtering graphite in Ar atmosphere mixed with different amount of acetylene.All substrates were ultrasonic cleaned in alcohol for 20 minutes to remove oil on the surface followed by hot air drying,and then fixed on the substrate holder.Before deposition,degassing was carried out by vacuum heating at 200℃until base pressure reached 3×10^(−3) Pa.After that,a plasma source with current of 50 A was applied to do Ar^(+)cleaning for 20 min,to further remove contaminants and activate substrate surfaces.500 nm Cr was deposited below the amorphous carbon layer to improve the adhesion strength between the substrate and the film.For amorphous carbon layer deposition,4 kW were applied on the graphite target while a–100 V negative bias was applied on the substrate.The argon flow rate was between 50-100 cm^(3)/min,and the acetylene flow rate changed from 0 to 100 cm^(3)/min to deposit amorphous carbon with various structures.In order to investigate effects of acetylene flow on microstructure,mechanical properties and tribological properties of films fabricated above,an X-ray photoelectron spectrometer and a Raman spectrometer were used to analyze microstructure,such as sp2,sp^(3),ID/IG,position and FWHM of D peak and G peak.Mechanical properties were characterized with a nanoindentor.The tribological properties were examined with a ball-disc tester,with load of 5 N,rotational speed of 1 m/s in air condition.The wear track on the film as well as the wear scar on the mated ball were tested with a white light interferometer and an optical microscope.The results showed that dense and uniform amorphous carbon film were prepared by reactive sputtering.Element analyzing demonstrated that all films contained a certain amount of O element(6.36%-13.86%)on the surface layer,O content of lower than 1%could be reached for most films after Ar^(+)etch.With the increase of acetylene flow rate,H,E and H^(3)/E^(2)increased first and then decreased.When acetylene flow rate was 10 cm^(3)/min,the hardness and elastic modulus reached maximum,which were 27.93 GPa and 233.55 GPa,respectively.Tribological results showed that the average friction coefficient was between 0.09-0.11 for all films,and the friction coefficient for the start-up stage decreased with the increase of H content.Wear resistance of 5 cm^(3)/min sample was the best,the minimum wear rate was 0.72×10^(−16)m^(3)/(N·m).The sp^(3)/sp^(2) and H can be tailored by adjusting acetylene flow in reactive sputtering,so as to regulate mechanical properties and tribological properties of amorphous carbon films.