金属学报, 2017, 53(7): 879-887
doi: 10.11900/0412.1961.2016.00436
碳基非晶镀层的纳米晶诱发机理及其摩擦学性能研究

Study on Nano-Crystallization Mechanism and Tribological Performance of Amorphous Carbon-Based Coatings
董丹, 蒋百灵, 郭萌, 杨超

摘要:

采用磁控溅射离子镀技术制备了一组不同Cr含量的碳基离子镀层,利用XRD、SEM、TEM、XPS及Raman光谱对镀层的微观结构进行了表征,并分析了微观结构对镀层的力学性能及摩擦学性能的影响。实验结果表明:随着Cr含量的增加,碳基镀层从典型的非晶结构转变为纳米晶/非晶复合结构,sp2杂化键含量逐渐增加,sp3杂化键含量逐渐减少,并且碳基镀层的硬度和内应力均随着Cr含量的增加而呈现减小的趋势。微量的金属Cr掺杂可有效地降低镀层的摩擦系数和比磨损率。过量的Cr掺杂虽有利于sp2杂化键含量的提高,但金属相的弥散分布导致了碳基镀层摩擦系数和比磨损率的增大,摩擦学性能变差。

关键词: 碳基镀层 ; Cr含量 ; 微观结构 ; 摩擦学性能

Abstract:

Amorphous carbon coatings mainly composed of sp3 and sp2 bonds have a great potential to be widely used in modern industry for their attractive properties, such as high hardness, high wear resistance and low friction coefficient. However, the high internal stress and poor adhesion of amorphous carbon coatings limit the range of industrial applications. In order to reduce the internal stress and improve the tribological performance, a series of carbon-based coatings with different atomic fraction of Cr were prepared by magnetron sputtering. The microstructure of coatings was characterized by XRD, SEM, TEM, XPS and Raman spectra. The mechanical and tribological properties of coatings were analyzed. The results showed that with the increase of atomic fraction of Cr, the carbon-based coatings changed from amorphous structure to nano-crystalline/amorphous composite structure, the ratio of sp2 bond increased and the ratio of sp3 bond decreased gradually. Also, the hardness and the internal stress showed a decreasing trend with the increase of atomic fraction of Cr. In addition, a small amount of Cr doping could effectively reduce the friction coefficient and specific wear rates of coatings. Excessive Cr doping is beneficial to the increase of the ratio of sp2 bond, however, the dispersion distribution of the metal phase leads to the increase of the friction coefficient and specific wear rates, so that the tribological properties were deteriorated.

Key words: carbon-based coating ; Cr content ; microstructure ; tribological performance

随着现代化工业的日益发展,越来越多的机械部件开始朝着高精度、高速度、高质量的水平发展,作为机械部件的主要基础件——轴承的摩擦失效问题越来越突出。精密机械传动系统中,由于其相对运动部件之间几乎是零间隙装配,传统的通过在摩擦副之间形成连续油膜来隔离部件以减少磨损的“引入润滑介质实现减磨延寿”的制造理念已很难实现。例如在谐波减速器中的柔性轴承因难以形成连续油膜而处于钢与钢之间的直接接触摩擦,其摩擦系数(一般大于0.5[1])远大于形成连续油膜的摩擦副之间10-2 [2~4]数量级的摩擦系数,从而导致摩擦副过早失效,严重缩短工件的使用寿命。而为解决此类有相对运动精密机械基础件的“减磨延寿”问题,在其表面制备1 μm左右厚度的高导热、低摩擦系数并有纳米金属微晶起增韧作用的碳基离子镀层的表面处理成为有效途径。

在过去的几十年中,由于工业需求对固体润滑材料的推动,CNx薄膜、类金刚石薄膜、类石墨薄膜等诸多碳基镀层得到了迅速发展[5~7]。类金刚石碳膜(DLC)以sp3杂化键结构为主,具有较高的硬度及较好的摩擦学性能[8],但同时因其较差的膜基附着力及高内应力,严重限制了此类固体润滑材料的工程应用[9~11]。而类石墨薄膜(GLC)是一种以sp2杂化键为主要化学键结构的无定形碳质材料,非晶基质中同时含有纳米量级形态各异的碳团簇[12~14],表现出更为良好的自适应减摩抗磨特性,可为大量处于干摩擦及混合摩擦状态下的摩擦副零部件提供有效的润滑剂防护[15~17],具有更为广阔的应用前景。20世纪80年代以来,大量研究[18~26]表明,给纯碳类石墨碳镀层中掺入Cr、Ti、W、Mo等过渡金属元素可有效缓解其高脆性及较差的附着力。其中,Yang等[27,28]的研究表明,Cr作为掺杂金属引入非晶碳基镀层中,能与C键合形成碳化物纳米晶镶嵌在非晶碳基质中,有效地缓解碳基离子镀层的内应力和提高膜基附着力,改善碳基离子镀层的高脆性及机械摩擦学行为。虽然人们研究了很多掺杂类石墨碳基镀层的性能,但掺杂金属诱发碳基镀层微观结构的改变以及微观结构差异对镀层性能影响的机理均了解不够透彻。

本工作利用磁控溅射离子镀沉积技术,制备了一组不同Cr含量的碳基离子镀层,研究了金属Cr掺杂诱发碳基离子镀层纳米晶/非晶复合结构产生的机理,讨论了Cr含量对碳基离子镀层的力学及摩擦学性能的影响机制。

1 实验方法

实验采用MSIP019型闭合场非平衡磁控溅射离子镀设备沉积不同Cr含量的碳基离子镀层。设备真空腔直径450 mm、高400 mm,平面阴极靶材为高纯C靶(约99.99%)及Cr靶(约99.99%)各一块,对称布置于圆柱形炉腔两侧,靶材直径100 mm,通过调整阴极磁铁排布及磁场强度将靶材表面放电面积缩小至45 cm2左右。实验基体选取P型(100)单晶Si片和M2高速钢片,其中,单晶Si片主要用于检测镀层的微观结构、内应力以及力学性能;高速钢片主要用于检测镀层的摩擦学性能。基体材料在使用前分别采用CH3COCH3 (丙酮)和CH3CH2OH (乙醇)溶液各超声波清洗20 min,清洗完成后用N2吹干放置于真空腔内120 mm处。实验在高纯Ar气氛中进行,真空度抽至3.0×10-3 Pa以上,气压保持在1.1×10-2~1.2×10-2 Pa范围内。碳基离子镀层的制备过程主要包括等离子体清洗、沉积纯Cr打底层、沉积过渡层和沉积工作层4个步骤。沉积工作层时,C靶电流为1.5 A,基体偏压为-60 V,沉积时间为2 h,通过改变Cr靶电流调节工作层Cr含量,具体实验参数如表1所示。

表1 碳基离子镀层的沉积参数
Table 1 Deposition parameters of carbon coatings
Sample No. I / A U / V p / (Wcm-2) cCr / % d / nm
1 0 0 0 0.0 869
2 0.05 300 0.33 2.0 894
3 0.10 320 0.71 6.5 1067
4 0.20 330 1.50 17.3 1094
5 0.30 340 2.30 25.5 1227

Note: I—target current, U—target voltage, p—target power density, cCr—atomic fraction of Cr, d—thickness

表1 碳基离子镀层的沉积参数

Table 1 Deposition parameters of carbon coatings

利用JSM-6700F场发射扫描电子显微镜(SEM)和Dimension Icon型原子力显微镜(AFM)观察镀层表面与截面的微观形貌;利用Renishaw inVia Relfex型Raman光谱仪对镀层进行结构分析;利用AXIS ULTRA型X射线光电子能谱(XPS)分析镀层的元素组成及化学状态;利用XRD-7000S型X射线衍射仪(XRD)分析镀层的相结构,Cu靶(波长为0.15406 nm),电压40 kV,电流30 mA,步长0.02°,扫描速率8°/min,扫描范围(2θ)为20°~80°;利用JEM-3010型透射电子显微镜(TEM)分析镀层的截面显微结构;用BGS 6341型电子薄膜应力分布测试仪分析镀层的内应力;利用Aligent Technologies Nano Indentor G200型纳米压痕仪分析薄膜的硬度及弹性模量;利用XLGT200型POD针盘式摩擦磨损实验机测试镀层的摩擦性能,所用摩擦副为直径5 mm的GCr15小球,测量转速为200 r/min,测试时间为30 min,相对湿度为50%~60%,温度为20~25 ℃。

2 实验结果与分析讨论
2.1 镀层的微观结构

5组不同Cr含量碳基镀层的表面形貌如图1所示。从图中可以看出,镀层基本呈岛状生长方式,表面呈大小不等的团簇,团簇之间有明显的界限。实验利用AFM对镀层的表面粗糙度(Ra)进行检测,5组试样的Ra分别为4.7、2.8、4.8、5.8和5.9 nm。当Cr含量为0 (纯C)时,镀层表面团簇之间界限细浅且团簇大小基本均等(图1a);当Cr含量增加到2.0%时,镀层表面团簇之间界限更加细浅,粗糙度降低且表面平整光滑,致密性良好(图1b);当Cr含量增加到6.5%时,镀层表面团簇颗粒直径减小,团簇之间界限增多(图1c);当Cr含量增加到17.3%时,镀层表面团簇颗粒更加细小,团簇之间界限变宽,致密性变差(图1d);当Cr含量进一步增加至25.5%时,镀层表面团簇起伏明显,粗糙度增大,团簇之间界限出现空隙,致密性进一步劣化(图1e)。因此,微量掺杂金属Cr元素有助于降低碳基镀层表面粗糙度,并提高其致密性,但掺Cr过多则有不利影响。

图1 不同Cr含量镀层的表面形貌

Fig.1 Surface morphologies of coatings with different atomic fractions of Cr(a) 0 (b) 2.0% (c) 6.5% (d) 17.3% (e) 25.5%

图2为5组不同Cr含量碳基镀层的Raman光谱。从图中可以看出,Raman光谱在1000~1800 cm-1处呈现出典型的非晶C的非对称特征峰,并且随着Cr含量的增加主峰的强度逐渐减弱。这是因为C元素有较强的光吸收性,Raman光谱主要检测分析C元素的吸收结果,随着Cr含量的增加,镀层中C元素比例及自由C的含量逐渐减少,峰强逐渐变弱。典型的非晶C膜Raman光谱主要由1350 cm-1附近的D峰和1560 cm-1附近的G峰构成,G峰和D峰都是由于C原子的sp2杂化键引起的,其中,G峰源于镀层中所有sp2态(环状或链状)的面内伸缩振动,D峰源于环状结构sp2态的呼吸振动[29~31]

图2 不同Cr含量镀层的Raman光谱

Fig.2 Raman spectra of coatings with different atomic fractions of Cr

Raman光谱拟合之后D峰和G峰的积分面积强度比(ID/IG)反映sp2环状结构的多少,G峰半高宽(FWHM(G))和G峰位置(Disp(G))反映薄膜的无序度,其中,FWHM(G)主要测量薄膜由键长和键角引起的结构上的无序,而Disp(G)主要测量薄膜中sp2团簇尺寸和形状引起的拓扑无序。5组不同Cr含量碳基镀层的Raman光谱的拟合结果如图3所示。从图中可以看出,随着Cr含量的增加,(ID/IG)呈现先升高后降低的趋势,在Cr含量为17.3%时(ID/IG)最大,(ID/IG)越大说明镀层中以离域形式存在的π键含量越少[32,33],即C-C键主要以sp2杂化键形式存在;随着Cr含量的增加,FWHM(G)先减小后增大,而Disp(G)则先增大后减小,这说明镀层中sp2团簇的有序度先增强后降低。由于Cr靶功率密度增大,沉积过程中粒子离化率增大且能量增强,sp2团簇增加的同时,能量的增加并未影响sp2杂化键的形状和尺寸;当Cr靶功率密度增大,能量进一步增强时,sp2杂化键的原有秩序被打乱,镀层的有序度降低。

图3 不同Cr含量镀层的ID/IG及G峰位置

Fig.3 ID/IG and G-peak position of coatings with different atomic fractions of Cr (FWHM(G)—full width at half maximum, Disp(G)—G peak dispersion, ID/IG—intensity ratio of D and G peaks)

图4为5组不同Cr含量镀层的C1s精细谱(XPS)。从图中可以看出,随着Cr含量的增加,C1s峰的强度逐渐减弱,这主要是Cr含量增大造成镀层中C含量相对减少的结果。石墨的C1s电子结合能在284.3 eV左右,而金刚石的C1s电子结合能在285.2 eV左右[34],图中镀层的C1s电子结合能均更接近于284.3 eV,则说明镀层中的C键结构主要以sp2杂化键为主。随着Cr含量的增加,C1s峰均比纯C镀层向结合能低的方向移动,说明sp2杂化键在C键中的比例增加。对C1s精细谱进行分峰拟合可得能量位于284.3 eV的sp2峰、285.2 eV的sp3峰、286.8 eV的C—O峰和288.5 eV的C=O峰,当Cr含量增大到一定值时,还会在282.1 eV处出现C—Cr峰[18]。拟合之后各价键比例如图5所示。随着Cr含量的增加,sp2杂化键比例从59.9%增加到79.2%,sp3杂化键比例从28.9%减少到8.6%,可见,金属Cr元素的添加促进了镀层的石墨化转变。随着Cr含量的增加,镀层中C—Cr键比例从0增加到7.0%,说明掺入Cr元素后,镀层微观结构中逐渐开始出现少量的碳铬化合物(有Cr23C6、Cr7C3及Cr3C2,主要为Cr3C2)纳米晶团簇。

图4 不同Cr含量镀层的C1s精细谱

Fig.4 C1s spectra of coatings with different atomic fractions of Cr

图5 不同Cr含量镀层的C1s精细谱拟合结果

Fig.5 Fitting results of C1s spectra of coatings with different atomic fractions of Cr

5组不同Cr含量镀层的XRD谱如图6所示。从图中可以看出,当Cr含量为0 (纯C)时,镀层的XRD谱为典型的非晶衍射峰,说明镀层为非晶相结构;当Cr含量从2.0%增加到25.5%时,图中逐渐出现微弱的晶相衍射峰,说明镀层中出现短程有序结构或尺寸极小的微晶粒,衍射峰强度随Cr含量的增加而增大,说明微晶粒的尺寸及数量随之增大。当Cr含量增加到一定程度时,镀层中形成大量尺寸很小的金属Cr或碳铬化合物等结晶相,镀层的微观结构由典型的非晶结构转变为纳米晶镶嵌在非晶基质中的纳米晶/非晶复合结构。

图6 不同Cr含量镀层的XRD谱

Fig.6 XRD spectra of coatings with different atomic fractions of Cr

图7为Cr含量为2.0%和25.5%时镀层的HRTEM像及SAED谱。从图7a中可以看出,Cr含量为2.0%时金属掺杂量较小,镀层的SAED谱呈弥散的圆晕状,表明其结构为典型的非晶态,由镀层的HRTEM像也可看出其呈均匀的非晶结构。结合前文中XPS及XRD的分析结果可知,虽然Cr含量为2.0%时镀层中有极少的C—Cr键形成,有微弱的晶化的趋势,但团簇短程有序度很低,不足以在镀层高分辨像中观察到明显的纳米晶粒。从图7b中可以看出,当Cr含量增加到25.5%时,镀层的SAED谱呈衍射环,镀层显微组织的晶态特征明显增强,表明此时镀层已由完全的非晶结构转变为纳米晶镶嵌在非晶基质中的纳米晶/非晶复合结构。图中深色区域为易形成纳米晶的富Cr区,浅色区域为易形成非晶结构的富C区,并且在图中可以观察到大量2~10 nm尺度的纳米晶粒团簇分散在非晶碳基质的局部区域。

图7 不同Cr含量镀层工作层的HRTEM像和SAED谱

Fig.7 HRTEM images and SAED patterns (insets) of working layer in coatings with 2.0%Cr (a) and 25.5%Cr (b)

结合以上微观结构分析可知,纯C镀层为典型的非晶结构,当Cr含量很小时,Cr原子完全溶解于非晶C镀层中,随着Cr靶功率密度的进一步增加,铬离子或活性基团含量及平均动能均随之增加,促使碳铬化合物的形成,当Cr含量超过一定范围,碳基镀层中会生成大量的金属Cr及碳铬化合物纳米晶粒,镀层从完全的非晶结构转变为纳米晶/非晶复合结构。

2.2 镀层的力学性能

图8为5组不同Cr含量镀层的力学性能测试结果。从图中可以看出,随着Cr含量的增加,镀层的内应力先显著减小后基本趋于平稳,镀层的硬度及弹性模量均随Cr含量的增加而呈减小的趋势。镀层内应力显著减小主要有以下3个原因:第一,最初Cr含量较小的溶解阶段,Cr原子易与C原子键合从而减少镀层中的悬挂键,降低了成键对方向性的束缚,缓解了镀层三维碳基网络结构中由于键角扭曲而产生的内应力,并且镀层中sp3杂化键含量降低,sp2杂化键含量趋于增多,内应力可通过sp2杂化C重新排列而释放;第二,Cr作为过渡族金属元素,其原子核对外层电子约束较小,而C原子与Cr原子键合可有效改变碳基网络结构的核外电子密度,从而抑制内应力的累积;第三,当Cr含量增加到一定程度时,镀层中出现纳米晶金属碳化物,其固有的弛豫作用及结构转化,降低了镀层生长过程中的内应力。原子键的结合键强度越大,受到外力作用时抵抗塑性变形的能力越强,表现出硬度就越大。要想获得高硬度的镀层,则需要高强度的共价键和短的键长,键能大、键长短的sp3杂化键是决定镀层硬度的主要因素。随着Cr含量的增加,镀层中sp3杂化键含量减小,sp2杂化键含量增大,并且结合图3可知,镀层中sp2杂化键有序度也相应提高,使得镀层的sp3/sp2比率迅速减小,镀层的硬度随之降低;另一方面,随着Cr含量的增加,镀层的致密度降低,也导致了镀层硬度的降低。

图8 不同Cr含量镀层的力学性能

Fig.8 Mechanical properties of coatings with different atomic fractions of Cr

2.3 镀层的摩擦学性能

图9为5组不同Cr含量镀层在不同环境条件下的摩擦系数。从图中可以看出,随着Cr含量的增加,镀层在干摩擦及谐波油润滑条件下的摩擦系数均先减小后增大,在Cr含量为2.0%时,摩擦系数有最小值,并且谐波油润滑条件下镀层的摩擦系数均小于干摩擦条件下的摩擦系数。在摩擦过程中,两个固体表面在一定压力作用下相互接触,相对移动时会发生物理粘着现象,碳基镀层表面在摩擦应力的热效应作用下会发生石墨化并生成转移膜,有效地降低镀层的磨损,提高了其耐磨性能[35,36]。当Cr含量为2.0%时,镀层中sp2杂化键含量增加有序度提高,有利于转移膜的生成,并且镀层组织均匀、致密度高且粗糙度小,有效地降低了镀层的摩擦系数;当Cr含量继续增加时,镀层组织的均匀性及致密性降低,粗糙度增大,并且形成大量的金属Cr及碳铬化合物等微晶组织,阻止摩擦面连续转移膜的形成,使镀层的摩擦系数增大。在谐波油润滑条件下,摩擦系数的变化较为平缓,润滑油膜使镀层与摩擦副无直接接触,并且润滑油膜厚度大、黏度高,剪切应力主要集中在润滑油膜内,减少微凸体之间的接触,剪切强度降低,从而降低了镀层的摩擦系数。

图9 不同Cr含量镀层的摩擦系数

Fig.9 Friction coefficients of coatings with different atomic fractions of Cr

5组不同Cr含量镀层在干摩擦条件下的比磨损率如图10所示。从图中可以看出,当Cr含量为2.0%时,镀层的比磨损率从9.4×10-16 m3/(Nm)降低到5.2×10-16 m3/(Nm),之后比磨损率随Cr含量的增加而增大,当Cr含量增加到25.5%时,镀层在实验时间内磨穿失效,说明掺入较少的金属Cr元素可以有效地降低镀层的比磨损率。

图10 不同Cr含量镀层的比磨损率

Fig.10 Specific wear rates of coatings with different atomic fractions of Cr

5组不同Cr含量镀层在干磨擦条件下的磨痕形貌如图11所示。从图中可以看出,纯C镀层的磨痕中间有微凸体划过的痕迹,即微凸体在镀层表面滑动形成犁沟,分布在磨痕中间位置,越靠中间犁沟痕迹越深,并且在边缘有被挤出的C粉材料堆积;当Cr含量为2.0%时,磨痕轨迹中未出现犁沟,磨痕较浅,是因为低的摩擦系数减轻了摩擦力;随着Cr含量的增加,磨痕进一步变宽但仍未出现较深的犁沟;当Cr含量为17.3%时,磨痕轨迹变深,出现明显的犁沟,并且在磨痕最深的位置有部分微小的脱落;当Cr含量为25.5%时,磨痕轨迹更加明显,且镀层有严重的脱落现象,脱落部分摩擦副直接与高速钢基体接触摩擦产生很深的痕迹,这是因为Cr含量过大使镀层的硬度和弹性模量大幅降低,承载能力变差导致耐磨性明显下降。

图11 不同Cr含量镀层的磨痕形貌

Fig.11 Wear tracks of coatings with different atomic fractions of Cr(a) 0 (b) 2.0% (c) 6.5% (d) 17.3% (e) 25.5%

镀层的耐磨性主要取决于其摩擦系数、硬度和显微组织等几方面因素。镀层的摩擦系数越小,硬度越高,则镀层的比磨损率越小。当Cr含量较小时,镀层的摩擦系数显著减小,镀层的硬度稍有降低,显微组织均匀致密,有助于降低镀层的比磨损率;当Cr含量进一步增加时,镀层中形成大量金属Cr和碳铬化合物等硬质颗粒,在摩擦过程中这些硬质颗粒与摩擦副产生磨粒磨损,加上镀层硬度的显著下降,使其比磨损率明显增大,加速了镀层的磨损,降低了镀层的耐磨性。

3 结论

(1) 微量掺杂金属Cr元素有助于降低磁控溅射离子镀技术制备的碳基镀层的表面粗糙度,并提高镀层致密性。

(2) 碳基离子镀层均以sp2杂化键为主,随着Cr含量的增加,镀层中的sp3杂化键含量减小,sp2杂化键含量增大,一定范围内提高了sp2杂化键的有序度,促使其发生石墨化转变。并且随着Cr含量的增加,镀层中C—Cr化合键含量增加,当Cr含量为25.5%时,出现大量2~10 nm的纳米晶团簇,其微观结构由典型的非晶结构转变为纳米晶/非晶复合结构。

(3) 碳基离子镀层的显微组织和sp2、sp3杂化键含量多少是影响其性能的主要因素,其硬度、弹性模量以及内应力均随着Cr含量的增加呈降低趋势,金属Cr元素的掺杂对碳基离子镀层有明显的去应力作用。在干摩擦及谐波油润滑条件下,镀层的摩擦系数和比磨损率均呈先减小后增大的趋势,当Cr含量为2.0%时,镀层的摩擦系数和比磨损率最小,微量金属Cr元素的加入可有效地改善碳基离子镀层的摩擦学性能。

The authors have declared that no competing interests exist.

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用离子束辅助非平衡中频磁控溅射技术,在Si,高速钢或不锈钢基体上分别沉积得到了具有多组分过渡金属层缓冲的W梯度掺杂类金刚石碳(DLC)膜,研究了W靶电流对DLC膜组成、结构和性能的影响。实验表明,随着W靶电流增大,薄膜中W掺杂量增加,W的碳化物含量增加,sp~3结构含量减少;薄膜的纳米硬度和弹性模量逐渐增大,且材料抗塑性参数H/E随之增大;随W靶电流增大,材料与基体结合力增强,划痕实验临界载荷在80—100 N之间,材料摩擦系数增大;但磨损率因W掺杂而明显减小,且随W靶电流增大而减小。样品表面元素分布均匀,粗糙度(R_a)较小,R_a值在7.56—15.8 nm之间。
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[21] Nie C Y, Zhang B Y, Xie H M.Structure analysis of Ti-doped DLC coatings deposited by unbalanced magnetron sputtering[J]. Acta Metall. Sin., 2007, 43: 1207
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(聂朝胤, 张碧云, 谢红梅. 非平衡磁控溅射掺Ti类金刚石薄膜的结构分析[J]. 金属学报, 2007, 43: 1207)
采用非平衡磁控溅射沉积技术在SCM415渗碳淬火钢基片上沉积 了无氢Ti掺杂类金刚石(Ti-DLC)薄膜和无氢高纯类金刚石(DLC)薄膜,通过调节Ti靶的溅射功率使获得的Ti-DLC薄膜Ti含量(原子分数) 为1.9%-34%.利用Raman分光光谱仪、XPS,XRD、显微硬度计及纳米划痕仪分析研究了Ti-DLC的组织结构、显微硬度及薄膜附着力.结果 表明,利用非平衡磁控溅射得到的Ti-DLC薄膜,在Ti含量小于25%时,Ti-DLC薄膜仍具有类金刚石薄膜的sp2,sp3结构,但Ti的掺杂促进 了sp3键向sp2键的转变.掺杂的Ti以TiC纳米晶的形式存在于非晶态的DLC中.掺杂Ti后薄膜的硬度明显降低,而薄膜附着力明显改善;但是当Ti 含量超过3%后,薄膜附着力无明显变化,硬度逐渐回升.
[22] Wu Z Z, Tian X B, Cheng S D, et al.Microstructure and mechanical properties of DLC films doped with high crystallinity CrN nanoparticles[J]. Acta Metall. Sin., 2012, 48: 283
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(吴忠振, 田修波, 程思达. 高结晶度CrN纳米粒子掺杂的DLC薄膜的显微结构及力学性能[J]. 金属学报, 2012, 48: 283)
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[23] Sheeja D, Tay B K, Sun C Q, et al.Characterization of Ti-containing amorphous carbon films prepared on titanium substrates[J]. J. Mater. Sci., 2003, 38: 421
Amorphous carbon (a:C) films prepared on pure titanium (Ti) substrates exhibit relatively high intrinsic compressive stress. In order to obtain low stress films with varied electrical and mechanical properties, metal (Ti) ions are incorporated into the plasma. This is done with the help of metal containing carbon targets. Amorphous carbon films with varied percentage of Ti were deposited on polished pure Ti substrates using Filtered Cathodic Vacuum Arc (FCVA) technique together with substrate pulse biasing. Characterizations of the films were carried out using various equipments including Raman Spectroscopy, X-ray diffractometer, Atomic Force Microscopy (AFM), Pin-on-Disk Tribometer and Micro-Scratch Tester; and properties such as microstructure, crystallography, film stress, morphology, frictional coefficient and critical load were investigated as a function of Ti content in the target. The results suggest that the film prepared with 5 at.% Ti-containing carbon target, under 7 kV substrate pulse bias voltage, displays almost zero stress. However such films are inferior in its Tribological properties compared to that of pure a:C films.
DOI:10.1023/A:1021807312324      URL     [本文引用:0]
[24] Wang A Y, Lee K R, Ahn J P, et al.Structure and mechanical properties of W incorporated diamond-like carbon films prepared by a hybrid ion beam deposition technique[J]. Carbon, 2006, 44: 1826
W incorporated diamond-like carbon films were prepared on silicon(1 0 0) wafers using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a tungsten DC magnetron sputter source. The W concentration in the films was controlled by changing the fraction of Ar in the Ar and C 6H 6 reaction gas. The chemical composition, atomic bond structure, and mechanical properties were investigated for W concentrations ranging from 0 to 8.6 at.%. When the W concentration was <2.8 at.%, the W atoms were dissolved in the amorphous carbon matrix without forming a WC 161 x phase. Amorphous and crystalline WC 161 x nano-particles appeared when the W concentration was >2.8 and >3.6 at.%, respectively. It was found that the hardness and elastic modulus were not sensitive to the W concentration in this concentration range. On the other hand, the residual compressive stress was strongly dependent on the chemical state of the incorporated W atoms. The change in mechanical properties is discussed in terms of the microstructural changes induced by W incorporation.
DOI:10.1016/j.carbon.2005.12.045      URL     [本文引用:0]
[25] Fu R K Y, Mei Y F, Fu M Y, et al. Thermal stability of metal-doped diamond-like carbon fabricated by dual plasma deposition[J]. Diamond Relat. Mater., 2005, 14: 1489
Metal incorporation into amorphous diamond-like carbon films can provide superior properties as metal nano-clusters or nanocrystalline metallic carbides can be embedded in the carbon network. In this work, a filtered metal plasma cathodic arc technique is used to generate a metal plasma and acetylene is introduced to the metal plasma plume to deposit metal-containing DLC (Me-DLC) films and form nanocrystalline carbide phases in the amorphous carbon matrix. The films exhibit high thermal stability up to annealing temperatures of 500 °C as revealed by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. At treatment temperature over 500 °C, a large amount of hydrogen is lost from the Me-DLC films as shown by elastic recoil detection. Breakdown and structural collapse of the film at high temperature can be attributed to the breaking of C–H bonds. Consequently, the C–C networks become more graphite-like to facilitate the formation of volatile C–O and metal oxides phases.
DOI:10.1016/j.diamond.2005.03.006      URL     [本文引用:0]
[26] Uglov V V, Kuleshov A K, Rusalsky D P, et al. Wear-resistant metal-carbon composite coating [J]. Surf. Coat. Technol., 2000, 128-129: 150
Carbon coatings containing a metallic component (zirconium, tantalum) were deposited with ion assistance on AISI M2 steel samples using a SVETLYACHOK source. The coatings were studied by Auger electron spectroscopy (AES), transmission electron microscopy (TEM), Raman spectroscopy (RS) and pin-on-disc tribological tests. The results have shown that the carbon coatings contain up to 20 at.% of the metallic component. These coatings have an amorphous structure with sp 3-type bonds. The presence of the coating on the surface of AISI M2 steel reduces the friction coefficient by a factor of five under the tribological conditions investigated. It is found that the tribological properties of the coatings deposited with the assistance of metal ions are significantly better than those coatings deposited with assistance of carbon ions. The latter coatings had carbon atoms with mixed sp 3顥竤p 2 bonds. The deposited composite carbon coatings are stable at a temperature of 100 C and allow a twofold improvement in the lifetime of fuel pump rods.
DOI:10.1016/S0257-8972(00)00573-9      URL     [本文引用:1]
[27] Yang S, Teer D G.Investigation of sputtered carbon and carbon/chromium multi-layered coatings[J]. Surf. Coat. Technol., 2000, 131: 412
Pure carbon and carbon/chromium multilayer coatings were deposited using unbalanced magnetron sputtering technology in a deposition system with a three-fold rotation turntable. The physical properties, microstructure and tribological performance of these coatings were investigated. The pure carbon coating was found to have a hardness of up to 4000 HV whilst the C/Cr multilayer coatings were in general softer with the exact hardness depending on the amount of Cr in the coatings. Keeping the sputtering power of carbon targets constant, a sputtering current on Cr was found that produced coatings with the best combination of properties of hardness of approximately 2200 HV and critical load of scratch ( L c) up to 85 N. The microstructures of the coatings were analysed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The tribological performance of the coatings was investigated using a pin-on-disc test. The pure carbon coating was found to have very good wear properties at low load whilst the coatings with optimized Cr content were found to have excellent tribological performance at high load. No failure was detected in 1 h running in the pin-on-disc test using a 5 mm WC ball rubbing against a coated M42 steel substrate at a speed of 200 mm/s with a load of 140 N and contact pressure higher than 3.4 GPa. Drilling tests under dry and un-lubricated conditions on C/Cr multilayer coated high-speed steel drills showed very good cutting performance with a lifetime three times longer than that of commercial TiN-coated drills.
DOI:10.1016/S0257-8972(00)00859-8      URL     [本文引用:1]
[28] Yang S, Li X, Renevier N M, et al. Tribological properties and wear mechanism of sputtered C/Cr coating [J]. Surf. Coat. Technol., 2001, 142-144: 85
Carbon/chromium (C/Cr) coatings were co-deposited using unbalanced magnetron sputtering deposition technique. The tribological properties including wear mechanism and microstructures of the coatings were investigated using pin-on-disc tribometer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The coatings were characterised by a high hardness (652200 HV), a low coefficient of friction (<0.1) and a very low wear rate under very high loads. The pin-on-disc tests of C/Cr coated tool steel against WC ball (5 mm of diameter) revealed low friction coefficient 0.06–0.1 depending on load and low wear rate 6510 6117 m 3/Nm with little dependence on load and sliding speed for the test using load up to 80 N and siding speed up to 400 mm/s for 1 h. Critical sliding speed was found above which, the wear rate was higher. The pin-on-disc tests of C/Cr coated austenitic 316 stainless steel against WC ball under a load of 10 N at siding speed of 400 mm/s for 1 h revealed a low friction coefficient 650.1 and a very low wear beyond the limitation of the as used wear measurement technique could detect. Microstructure of the coated stainless steel was investigated. XRD profiles of the coating exhibited typical patterns for amorphous-like material, with no crystal-like peaks identified. Cross-sectional TEM analysis of the rubbed tracks of the coated stainless steel revealed some deformation in the substrate near the interface. However, no sign of interfacial spallation was observed, indicative of excellent adhesion of the coating to the substrate. The selected area electron diffraction patterns taken from the rubbed and unrubbed regions of the coating were interpreted and discussed. The tribological performance of this novel C/Cr coating is believed to be closely related to its graphite nature. The high resolution TEM (HRTEM) cross-section analysis of the coating on stainless steel substrate revealed that the outer-most surface of the rubbed track was reoriented due to the rubbing in a 1-h pin-on-disc test under a load of 10 N. Finally, the relationship between deposition parameters and tribological performance of the coating is also discussed in this paper.
DOI:10.1016/S0257-8972(01)01147-1      URL     [本文引用:1]
[29] Ferrari A C, Robertson J.Interpretation of Raman spectra of disordered and amorphous carbon[J]. Phys. Rev., 2000, 61B: 14095
The model and theoretical understanding of the Raman spectra in disordered and amorphous carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of states and the long-range polarizability of bonding. Visible Raman data on disordered, amorphous, and diamondlike carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the spsites in sp-bonded clusters. In cases where the spclustering is controlled by the spfraction, such as in as-deposited tetrahedral amorphous carbon (ta-C) or hydrogenated amorphous carbon (a-C:H) films, the visible Raman parameters can be used to derive the spfraction.
DOI:10.1103/PhysRevB.61.14095      URL     [本文引用:1]
[30] Gradowski M V, Ferrari A C, Ohr R, et al. Resonant Raman characterisation of ultra-thin nano-protective carbon layers for magnetic storage devices [J]. Surf. Coat. Technol., 2003, 174-175: 246
Carbon thin films are very important as protective coatings for a wide range of applications such as magnetic storage devices. The key parameter of interest is the sp 3 fraction, since it controls the mechanical properties of the film. Visible Raman spectroscopy is a very popular technique to determine the carbon bonding. However, the visible Raman spectra mainly depend on the configuration and clustering of the sp 2 sites. This can result in the Raman spectra of different samples looking similar albeit having a different structure. Thus, visible Raman alone cannot be used to derive the sp 3 content. Here we monitor the carbon bonding by using a combined study of Raman spectra taken at two wavelengths (514 and 244 nm). We show how the G peak dispersion is a very useful parameter to investigate the carbon samples and we endorse it as a production-line characterisation tool. The dispersion is proportional to the degree of disorder, thus making it possible to distinguish between graphitic and diamond-like carbon.
DOI:10.1016/S0257-8972(03)00602-9      URL     [本文引用:0]
[31] Kanda K, Yamada N, Okada M, et al.Graphitization of thin films formed by focused-ion-beam chemical-vapor-deposition[J]. Diamond Relat. Mater., 2009, 18: 490
The effect of annealing on the structure of diamond-like carbon (DLC) thin film fabricated by focused-ion-beam chemical-vapor deposition (FIB–CVD) was investigated. The near-edge x-ray absorption fine-structure spectrum of the carbon K-edge over the excitation energy range of 275–32002eV was measured on the FIB–CVD DLC thin film by annealing for 102h in a temperature region from room temperature (RT) to 127302K. The sp 2/( sp 2 + sp 3) ratio maintained ≈ 0.4 in an annealing temperature region from room temperature to 52302K and steeply increased from ≈ 0.4 to ≈ 0.7 with annealing temperature from 52302K to 77302K. The I( D)/ I( G) ratio, which was obtained from the Raman spectrum, also indicated a similar dependence on annealing temperature. The graphitization of thin film fabricated by focused-ion-beam chemical-vapor deposition (FIB–CVD) by annealing was confirmed to start at ≈ 60002K.
DOI:10.1016/j.diamond.2008.10.013      URL     [本文引用:1]
[32] Liu L, Wang T, Huang J L, et al.Diamond-like carbon thin films with high density and low internal stress deposited by coupling DC/RF magnetron sputtering[J]. Diamond Relat. Mater., 2016, 70: 151
61Diamond like carbon films were deposited by coupling DC/RF magnetron sputtering.61The films prepared have high mass density and low internal stress.61The diamond like carbon films were deposited will be used in inertial confinement fusion (ICF) experiments.
DOI:10.1016/j.diamond.2016.10.004      URL     [本文引用:1]
[33] Chiu S M, Lee S C, Wang C H, et al.Electrical and mechanical properties of DLC coatings modified by plasma immersion ion implantation[J]. J. Alloys Compd., 2008, 449: 379
DLC (a-C:H) films were deposited by the plasma enhanced chemical vapor deposition (PECVD) on silicon substrate and then post-implanted by plasma immersion ion implantation (PIII) at different voltages and ion species (Ar, N 2 and C 2H 2). Microstructure, dielectric constant and nano-hardness of the modified DLC films were studied. It is found that implanted C 2H 2 ions can effectively increase the nano-hardness of DLC films from 13.5 to 25.3 GPa and reduce the dielectric constant to 2.5 in the bias voltage range of 6135 to 6140 kV. The improved properties are mainly associated with the increase in the ratio of sp 3 C C/sp 2 C C bonds and the reaction mechanisms in the implantation zone are discussed.
DOI:10.1016/j.jallcom.2006.02.108      URL     [本文引用:1]
[34] Tsai P C, Chen K H.Evaluation of microstructures and mechanical properties of diamond like carbon films deposited by filtered cathodic arc plasma[J]. Thin Solid Films, 2008, 516: 5440
Diamond-like carbon (DLC) films were deposited by a cathodic arc plasma evaporation (CAPD) process, using a mechanical shield filter combined with a magnetic filter with enhanced arc structure at substrate-bias voltage ranging from 61 50 to 61 30002V. The film characteristics were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties were investigated by using a nanoindentation tester, scratch test and ball on disc wear test. The Raman spectra of the films showed that the wavenumber ranging from 900 to 180002cm 61 1 could be deconvoluted into 114002cm 61 1, D band and G band. The bias caused a significant effect on the sp 3 content which was increased with the decreasing of I D/ I G ratio. The XPS spectra data of the films which were etched by H + plasma indicated the sp 3 content are higher than those of the as-deposited DLC films. This implied that there is a sp 2-rich layer present on the surface of the as-deposited DLC films. The nanoindentation hardness increased as the maximum load increased. A 38002nm thick and well adhered DLC film was successfully deposited on WC-Co substrate above a Ti interlayer. The adhesion critical load of the DLC films was about 3302N. The results of the wear tests demonstrated that the friction coefficient of the DLC films was between 0.12 and 0.2.
DOI:10.1016/j.tsf.2007.07.060      URL     [本文引用:1]
[35] Holmberg K, Ronkainen H, Laukkanen A, et al.Friction and wear of coated surfaces-scales, modelling and simulation of tribomechanisms[J]. Surf. Coat. Technol., 2007, 202: 1034
Coating a surface with a thin layer changes the surface material properties and is an important tool for controlling friction and wear. The tribological mechanisms, scale effects and parameters influencing the friction and wear of coated surfaces are discussed. The basic friction and wear mechanisms can be reduced to: friction by adhesion, ploughing and hysteresis and wear by adhesion, abrasion and fatigue combined with material fracture. The tribochemical and surface physical effects and surface fatigue taking place before material fracture are treated here as pure surface material modification mechanisms. Scale effects in a tribological contact are illustrated by explaining typical surface roughness related tribological mechanisms for diamond and DLC coated surfaces. For diamond coatings asperity interlocking effects are important for rough surfaces, graphitisation is a dominating mechanism for smooth engineering surfaces and hydrogenising of dangling bonds may be crucial for physically smooth surfaces. For DLC coated surfaces, surface graphitisation is important with rougher surfaces; building up transfer layers and graphitisation is crucial for smooth engineering surfaces and hydrogenising of dangling bonds can explain superlubricity for physically smooth surfaces. An analysis of dominating surface parameters such as elastic, plastic and fracture behaviour of the top surface, the coating, the coating/substrate interface and the substrate in addition to the coating thickness forms the basis for surface modelling. A stress intensity factor analysis of crack growth shows the importance of considering both modes I, II and III loading, crack spacing and location of crack, while crack orientation, location in crack field as well as load biaxiality have minor influences. It is shown how surface 3D FEM modelling generates stress and strain values at the nano level, within bond layers at coating/substrate interfaces and around cracks and forms the basis for better understanding the origin of wear.
DOI:10.1016/j.surfcoat.2007.07.105      URL     [本文引用:1]
[36] Wang Y X, Wang L P, Li J L, et al.Tribological properties of graphite-like carbon coatings coupling with different metals in ambient air and water[J]. Tribol. Int., 2013, 60: 147
78 GLC coating exhibits different tribological properties against metals. 78 The differences are highly dependent on adhesions and wear behaviors of the metals. 78 GLC coating could show low friction and wear against GCr15 and Ti in air. 78 GLC coating is more suitable to machine common metals in water.
DOI:10.1016/j.triboint.2012.11.014      URL     [本文引用:1]
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关键词(key words)
碳基镀层
Cr含量
微观结构
摩擦学性能

carbon-based coating
Cr content
microstructure
tribological performance

作者
董丹
蒋百灵
郭萌
杨超

DONG Dan
JIANG Bailing
GUO Meng
YANG Chao