Cross-sectional nanoindentation and nanoscratch of compositionally graded mullite films

Nanoindentation and nanoscratch have become well-established techniques for measuring mechanical properties of thin films. Conventionally, these tests are performed on the surface of the films to evaluate their mechanical integrity: elastic modulus, hardness and adhesion strength. However, in complex systems such as compositionally graded thin films, small spatial variations in mechanical properties are difficult to distinguish using this approach. In this work, the evaluation of the above parameters was conducted on cross-sections of compositionally graded mullite coatings, chemical-vapor deposited on silicon carbide substrates. To assess the intrinsic mechanical properties and their spatial variation, nanoindentation tests were carried out on mullite coatings with constant and graded Al/Si ratios. Additionally, transverse nanoscratch tests to evaluate the cohesive and adhesive resistance of the coatings as well as the coating/substrate systems, respectively, were performed. Different damage morphologies were identified within the coating and at the interface by using complementary characterization techniques. In the case of functionally graded coatings a gradual rise in the hardness and elastic modulus with increasing distance from the coating/substrate interface was observed. Nanoscratch tests on the cross-sections allowed determining the critical loads for cohesive and adhesive damage by following this approach. Compositionally graded mullite coatings exhibited the best combination of hardness/stiffness and cohesive/adhesive scratch strength.     

DLC and UHMWPE as hard/soft composite film on Si for improved tribological performance

The main purpose of this study is to explore the advantages of using a composite thin film of ultra high molecular weight polyethylene (UHMWPE) on a hard diamond like carbon (DLC) coating deposited on Si, for high wear life and low coefficient of friction. The experiments are carried out using a ball-on-disc tribometer at a constant linear speed of 0.052 m/s. A 4 mm diameter silicon nitride ball with a normal load of 40 mN is used as the counterface. The tribological results are discussed on the basis of hardness, elastic modulus, contact area, contact pressure and optical images of surface films. As a result of higher load carrying capacity (high hardness and elastic modulus), the wear life of Si/DLC/UHMWPE coated layer is approximately five times greater than that of Si/UHMWPE. Looking at the film thickness effect, UHMWPE film shows maximum wear resistance when the film is of optimum thickness (6.2 μm-12.3 μm) on DLC. Wear mechanisms of different UHMWPE thicknesses for Si/DLC/UHMWPE film are explained using optical microscopy of worn surfaces. Further, the use of perfluoropolyether (PFPE) ultra-thin film as the top layer on the composite coatings reduces the coefficient of friction to very low values (0.06-0.07) and increases the wear life of the films by several folds.     

Ti/Al过渡层对共掺杂类金刚石薄膜性能的影响

目的研究Ti/Al过渡层对不同溅射电流下的Ti/Al共掺杂DLC薄膜的成分、结构、机械性能和结合力的影响。方法采用线性离子束复合磁控溅射技术在316L基底上沉积含有Ti/Al过渡层的Ti/Al共掺杂DLC薄膜,利用场发射扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)、高分辨透射电镜(HRTEM)及共聚焦激光拉曼光谱仪分析了薄膜的界面形貌及键态结构。采用辉光放电光谱仪对样品成分进行深度分析,纳米压痕仪测量薄膜硬度及弹性模量,划痕测试系统测量膜基结合力,残余应力仪测量薄膜内应力。结果与未添加过渡层相比,添加Ti/Al过渡层对薄膜的结构和机械性能影响较小,且均在溅射电流为2.5 A时有最优的机械性能;然而,溅射电流为2.5 A时,添加过渡层使结合力从54.5 N提高到了67.2 N,提高了19%,残余应力从1.28 GPa降低到了0.25 GPa,降低了80%。结论 Ti/Al过渡层可缓解因DLC薄膜和基体的晶格匹配差异和膨胀系数不同而导致的高界面应力。在薄膜与基底界面,过渡层呈现典型柱状晶结构,可促进膜基界面间的机械互锁,显著改善薄膜与基体之间的结合力而不损伤其机械性能。     

Preparation of diamond-like carbon by PBII-enhanced microwave ECR chemical vapor deposition

Diamond-like carbon (DLC) films were fabricated with methane on the surface of Si(100) wafer by combining plasma-based ion implantation and microwave ECR chemical vapor deposition. Raman scattering spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemical structure of the DLC films and sp³ content of the DLC films was measured by XPS. Atomic force microscope was employed to investigate the surface morphology information of DLC films synthesized by different methods. The hardness of the films was evaluated using microindentation techniques. Results showed that plasma-based ion implantation enhanced ECR chemical vapor deposition could result in the better surface morphology, the higher adhesion strength and the enhanced hardness; in addition, the hardness of the DLC films was elevated by doping with nitrogen.     

A combinatorial thin film sputtering approach for synthesizing and characterizing ternary ZrCuAl metallic glasses

We report a combinatorial sputtering approach for synthesizing ternary metallic glass alloys on both silicon and sapphire substrates. ZrCuAl metallic-glass thin films were co-deposited using a multi-source radio-frequency magnetron-sputtering process. The combinatorial synthesis process yields a wide range of compositions via a single co-sputter deposition process. The compositions of the films were characterized by the energy-dispersive X-ray spectroscopy (EDS), and the structure of the ZrCuAl alloy thin films was investigated by the X-ray diffraction (XRD). Thorough phase analyses indicated the phases present in the films at different compositions were in good agreement with the binary Zr–Cu phase diagram. Nanoindentation results showed that mechanical properties of the bulk-metallic glasses (BMGs) thin film, such as elastic modulus and hardness, are functions of the Zr (or Cu) concentration. The composition with a moderate Zr content (45 atomic percent (at.%)) resulted in a high film modulus and hardness. The post anneal treatment increased the film elastic modulus and hardness. Small additions of aluminum slightly enhanced the film mechanical properties. Using this combinatorial technique could facilitate the development of the new multi-element metallic-glass alloy, particularly for systems with many elements. The first attempt of casting the optimum resultant ternary BMGs rod was successful.     

Evaluation of elastic properties of DLC layers using resonant ultrasound spectroscopy and AFM nanoindentation

Elastic properties of diamond-like carbon (DLC) layers with gradient carbon–silicon interlayer were studied by resonant ultrasound spectroscopy (RUS) and standard nano-indentation technique. The DLC layers were prepared by pulsed laser deposition on SiC/Si substrates. The RUS method is based on modal analysis of the specimen vibration. The resonant frequency shifts caused by the layer are for the evaluation of the dynamic in-plane elastic properties of the deposited DLC. The results were compared with the quasi-statical quantities — Young's modulus and hardness, obtained by nanoindentation using the AFM tip.     

镁合金表面磁控溅射DLC/SiC薄膜的纳米压痕与摩擦磨损性能

采用室温磁控溅射技术在镁合金(AZ91D)表面制备出DLC/SiC(类金刚石/碳化硅)双层薄膜(SiC为中间层),研究了薄膜的纳米压痕行为、膜基黏附力和膜基系统的摩擦磨损性能.结果表明:DLC薄膜具有低的纳米硬度(3.05 GPa)、低的弹性模量(24.67 GPa)和高的硬弹比(0.122);膜基系统具有高的界面黏附力和好的摩擦磨损性能;在以氮化硅球为对摩件的室温干摩擦条件下其磨损速率在10~(-6)mm~3·m~(-1)·N~(-1)级,摩擦系数约为0.175.分析表明:膜基系统具有的良好抗磨性能与其薄膜具有高的塑性和硬弹比、膜基系统具有好的弹性模量匹配是相一致的;DLC薄膜具有的不寻常力学行为(很低的硬度和弹性模量等)与其基材是镁有关.     

DLC基纳米多层膜摩擦学性能的研究进展与展望

类金刚石（DLC）薄膜是一种良好的固体润滑剂,能够有效延长机械零件、工具的使用寿命。DLC基纳米多层薄膜的设计是耐磨薄膜领域的一项研究热点,薄膜中不同组分层具备不同的物理化学性能组合,能从多个角度（如高温、硬度、润滑）进行设计来提升薄膜力学性能、摩擦学性能以及耐腐蚀性能等。综述了DLC多层薄膜的设计目的与研究进展,以金属/DLC基纳米多层膜、金属氮化物/DLC基纳米多层膜、金属硫化物/DLC基纳米多层膜以及其他DLC基纳米多层膜为主,对早期研究成果及现在的研究方向进行了概述。介绍了以上几种DLC基纳米多层膜的现有设计思路（形成纳米晶/非晶复合结构、软/硬交替沉积,诱导转移膜形成,实现非公度接触）。随后对摩擦机理进行了分析总结：1）层与层间形成特殊过渡层,提高了结合力;2）软/硬的多层交替设计,可以抵抗应力松弛和裂纹偏转;3）高接触应力和催化作用下诱导DLC中的sp3向sp2转化,形成高度有序的转移膜,从而实现非公度接触。最后对DLC基纳米多层膜的未来发展进行了展望。     

偏压对电弧离子镀沉积类金刚石膜的影响

采用电弧离子镀方法，在Si(100)基底上沉积了类金刚石(DLC)膜．用激光Raman谱和X射线光电子能谱(XPS)对不同偏压下沉积的类金刚石膜的结构进行了分析．结果表明，Raman谱的D峰和G峰的强度之比ID／IG随着脉冲负偏压的增加先减小后增大，sp^3键含量随着负偏压的增加先增加后减小．偏压为-200V时，ID／IG值最小为0．70，sp^3键含量最大为26．7％．纳米压痕仪测量结果表明，随着咏冲负偏压增加，硬度和弹性模量先增加后下降．偏压为-200V时，DLC膜的硬度和弹性模量最大，分别为30．8和250．1GPa．     

Effects of Al Content on Microstructure and Mechanical Property of CrAlN Coating Synthesized by Reactive Magnetron Sputtering

A series of CrAlN coatings with different Al content were synthesized on high-speed steel(M2)substrate by reactive direct current(DC)magnetron sputtering.The influences of Al content on the microstructure and mechanical property of CrAlN coatings were studied by scanning electron microscopy(SEM),X-ray diffraction(XRD),energy dispersive spectrum(EDS)and nano-indentation techniques,respectively.The results indicate that the coatings exhibit only fcc c-CrN phase when Al content is less than 65 at%,and fcc c-CrN and c-AlN phases when Al content is 78 at%.The coating with Al content of 60 at%exhibits high hardness and elastic modulus.The maximum hardness and elastic modulus values could reach 36.8 GPa and 459.5 GPa,respectively.     

反应溅射TiC薄膜的微结构及力学性能

采用反应磁控残射法在不同的甲烷分压下制备了一系列的TiC薄膜，利用XRD和TEM表征了薄膜的相组成和微结构，用力学探针测量了薄膜的硬度和弹性模量，并利用AFM观察了薄膜的生长形貌和压痕形貌，研究了甲烷分压对薄膜相组成、微结构和力学性能的影响。结果表明，甲烷分压对薄膜的相组成、微结构和力学性能均有明显的影响：低的甲烷分压下，制备的薄膜样品中有仗相的存在，薄膜的硬度和弹性模量较低；甲烷分压提高0.02～0.04Pa左右，薄膜内形成晶粒细小的单相TiC，并获得最高的硬度(30．9GPa)和弹性模量(343GPa)；进一步提高甲烷分压，薄膜互现非晶态，其硬度和弹性模量亦随之降低。     

Microstructure and mechanical property evaluation of pulsed DC magnetron sputtered Cr–B and Cr–B–N films

CrB₂ and four Cr–B–N films with high Cr/B ratio and various nitrogen contents were deposited by a co-sputtering process using a bipolar asymmetric pulsed DC reactive magnetron sputtering system. The structures and BN bonding nature of the thin films were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The surface and cross sectional morphologies of the thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface roughness of the thin films was explored by atomic force microscopy (AFM). Nanoindentation, microscratch and ball-on-disk wear techniques were used to evaluate the hardness, and tribological properties of the thin films, respectively.The microstructure of the Cr–B–N thin films changed from a coarse columnar structure to a glassy and featureless morphology as the nitrogen content increased from 15.2 at.% to 54.5 at.%, whereas the corresponding structure developed from an amorphous state to a nanocomposite structure consisting of CrN nanograins and amorphous BN phases. It was found that high hardness, good tribological and brittle properties were obtained for the CrB₂ coating. The hardness and elastic modulus of the Cr–B–N thin films decreased with increasing nitrogen content until the nanocomposite structure of nanocrystalline CrN grains and an amorphous BN matrix was formed. However, the hardening effect induced by the nanocomposite structure was limited due to the fact that the small CrN nanograins were surrounded by a thick intergranular soft amorphous BN layer. On the other hand, the fracture toughness and resistance against elastic strain to failure of the Cr–B–N coatings were effectively enhanced by the addition of nitrogen.     

掺Ti量对类金刚石薄膜机械性能的影响

采用非平衡磁控溅射技术,通过改变Ti靶溅射电流,在不锈钢衬底表面沉积了不同掺Ti量的类金刚石薄膜(Ti-DLC),研究了掺Ti量对薄膜的显微硬度、弹性模量、膜/基结合强度、断裂韧性及摩擦磨损行为的影响。结果表明:DLC薄膜掺杂Ti后,硬度明显提高,且随着Ti靶溅射电流的增大,薄膜硬度先增加、后降低,Ti靶溅射电流为1.5A时,薄膜硬度最高;掺杂适量的Ti,可以明显改善DLC薄膜的膜/基结合强度和断裂韧性,并能明显降低DLC薄膜的摩擦系数。     

Deposition,microstructure and hardness of TiN/(Ti,Al)N multilayer films

In this work, TiN/(Ti,Al)N multilayer films were deposited on stainless steel substrates with alternatively switching Ti and TiAl alloy targets sources on and off by pulse biased arc ion plating. The crystallography structures and cross-sectional structures of TiN/(Ti,Al)N multilayer films were evaluated by X-ray diffraction analysis (XRD) and by TEM, respectively. The hardness and film/substrate adhesion were determined by nanoindentation and scratch test, respectively. A complex set of microstructures has been found between TiN and (Ti,Al)N layers, at the interface, another layered interfacial region which consists of extremely fine sub-layers, which results from the rotation of the specimen in the deposition chamber. The hardness values of the multilayers exhibit higher hardness compared with that of monolithic (Ti,Al)N film.     

Deposition and properties of Al-containing diamond-like carbon films by a hybrid ion beam sources

Metal incorporation is one of the most effective methods for relaxing internal stress in diamond-like carbon (DLC) films. It was reported that the chemical state of the incorporated metal atoms has a significant influence on the film internal stress. The doped atoms embedding in the DLC matrix without bonding with C atoms can reduce the structure disorder of the DLC films through bond angle distortion and thus relax the internal stress of the films. In present paper, Al atoms, which are inert to carbon, were incorporated into the DLC films deposited by a hybrid ion beams system comprising an anode-layer ion source and a magnetron sputtering unit. The film composition, microstructure and atomic bond structure were characterized using X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. The internal stress, mechanical properties and tribogoical behavior were studied as a function of Al concentration using a stress-tester, nanoindentation and ball-on-disc tribo-tester, respectively. The results indicated that the incorporated Al atoms were dissolved in the DLC matrix without bonding with C atoms and the films exhibited the feature of amorphous carbon. The structure disorder of the films tended to decrease with Al atoms incorporation. This resulted in the distinct reduction of the internal stress in the films. All Al-DLC films exhibited a lower friction coefficient compared with pure DLC film. The formation of the transfer layer and the graphitization induced by friction were expected to contribute to the excellent friction performance.     

钛合金表面大气压等离子体枪制备类金刚石薄膜

在大气下,采用大气压介质阻挡放电(DBD)等离子体枪在低温下(350℃),以甲烷为单体,氩气为工作气体,在Ti6Al4V钛合金表面制备一层类金刚石薄膜(DLC),以期改善钛合金表面摩擦学性能。利用激光拉曼(Raman)光谱和X射线光电子能谱(XPS)分析了所制备DLC薄膜的结构;利用扫描电子显微镜(SEM)观察DLC薄膜的表面形貌;利用划痕仪测量了DLC薄膜与基体的结合力;利用球-盘摩擦磨损实验仪对DLC薄膜的耐磨性能进行了研究。结果表明:在本实验工艺条件下沉积的类金刚石薄膜厚度约为1.0μm,薄膜均匀且致密,表面粗糙度Ra为13.23nm。类金刚石薄膜与基体结合力的临界载荷达到31.0N。DLC薄膜具有优良的减摩性,Ti6Al4V表面沉积DLC薄膜后摩擦系数为0.15,较Ti6Al4V基体的摩擦系数0.50明显减小,耐磨性能得到提高。     

Composition and structure of Ti-C/DLC graded composite films

The Ti-C→DLC gradient composite films were characterized systematically.The elemental depth profile and elemental chemical state evolution were determined by X-ray photoelectron spectroscopy (XPS).The transmission electron microscope (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to study the structure of interfacial zone between DLC film and Ti-C layers.Results show that there are composition transition zone between DLC film and either Ti-C layer or steel substrate on condition that pre-deposited Ti layers on the steel substrate then plasma based bias deposited DLC films.In Ti-C graded layer,the chemical state of titanium and carbon are changed gradually.The structures of zone in Ti-C layer near the DLC film is consisted of random oriented nanocrystallines TiC dispersed in amorphous DLC matrix.The structure of the zone between DLC film and Ti-C graded layer is gradually changed too.     

不同过渡层对DLC薄膜力学性能和摩擦学性能的影响

薄膜与基体间的界面结合性能是决定薄膜性能发挥的关键要素。针对类金刚石薄膜(DLC)在硬质合金上结合力差的问题,采用线性阳极离子束复合磁控溅射技术在硬质合金YG8基体上设计制备了单层W过渡层、WC过渡层、双层W过渡层和三层W过渡层4种不同W过渡层的DLC薄膜,探讨了不同过渡层对DLC薄膜力学和摩擦学性能的影响。结果表明:不同过渡层结构的DLC薄膜结构致密,界面柱状生长随着层数增加及过渡层厚度的降低而打断,有利于改善薄膜的韧性。当为三层W过渡层时,DLC薄膜的断裂韧性达到最大值6.44 MPa·m1/2;与单层W过渡层相比,薄膜硬度有小幅下降,但薄膜内应力降低了55%,且膜/基匹配性更佳,结合强度高达85N,此时薄膜具有较低的摩擦因数和磨损率,表现出比较优异的抗磨减摩性能。     

Use of diamond-like carbon with tungsten (W-DLC) films as biocompatible material

Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), are a class of materials with excellent mechanical, tribological and biological properties. When the DLC films are enhanced with other elements, all of these properties can be changed within a certain range.In this work, reactive magnetron sputtering was used to deposit W-DLC (hydrogenated tungsten carbide) films on Ti6Al4V (implant material). Many films were made using pure tungsten (99.99%) target and different plasmas processes, with different ratio among argon and methane. It was possible to change the films composition (from pure amorphous carbon to carbon enhanced with tungsten) according to ratio of argon and methane plasma. Between all films processed, the carbon films enhanced with tungsten showed good results in the “in vitro” cytotoxicity testing. Raman spectroscopy was used to analyze the chemical bonds kinds and the chemical bonds quantities. The Rutherford Back Scattering (RBS) was used to analyze the films compositions. The chemical inertness was analyzed by scanning voltametry. W-DLC thin films obtained in these processes have low roughness, high chemical resistance, good adhesion and show a high biocompatibility, when compared with common DLC thin films. Hence we have concluded that the tungsten concentrations in the DLC films make an important role to improve the properties of the DLC layers.     

Effects of the substrate on the determination of thin film mechanical properties by nanoindentation

We examine the effects of the substrate on the determination of mechanical properties of thin films by nanoindentation. The properties of aluminum and tungsten films on the following substrates have been studied: aluminum, glass, silicon and sapphire. By studying both soft films on hard substrates and hard films on soft substrates we are able to assess the effects of elastic and plastic inhomogeneity, as well as material pile-up, on the nanoindentation response. The data set includes Al/glass and W/sapphire, with the film and substrate having nearly the same elastic properties. These systems permit the true contact area and true hardness of the film to be determined from the measured contact stiffness, irrespective of the effects of pile-up or sink-in. Knowledge of the true hardness of the film permits a study of the effects of the elastic modulus mismatch on the nanoindentation properties, using the measured contact stiffness as a function of depth of indentation.