Plasma immersion ion implantation induced improvements of mechanical properties, wear resistance, and adhesion of diamond-like carbon films deposited on tool steel

Nitrogen-rich layers are formed on the surface of JIS-SKH51 tool steel substrates using the plasma immersion ion implantation (PIII) technique. An unbalanced magnetron sputtering (UBMS) system is then used to coat the steel substrates with diamond-like carbon (DLC) films of various thicknesses. The adhesive strength and wear resistance of the DLC films are then examined by performing nanoscratch and nanowear tests. Finally, the microstructures of the DLC films are analyzed using TEM and Raman spectroscopy. The nanoindentation test results show that the PIII treatment yields an effective improvement in both the hardness and the Young's modulus of the SKH51 substrates. Moreover, cross-sectional observations show that the implantation depth and microstructure of the nitrogen-rich surface layer are dependent on the nitrogen/hydrogen flow ratio used in the PIII process. The nanoscratch test results show that the PIII treatment improves the adhesion of the DLC film to the steel substrate. Furthermore, the Raman spectroscopy results indicate that the use of hydrogen in the PIII process limits the increase in the I(D)/I(G) ratio by increasing the DLC film thickness. Finally, the nanowear test results show that the deposition of a DLC coating with a sufficient thickness yields a significant improvement in the wear resistance of the steel substrate.     

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.     

Effects of N-doping on the microstructure, mechanical and tribological behavior of Cr-DLC films

We report on the effects of nitrogen doping on Cr-containing diamond-like carbon (Cr-DLC) films. DLC, Cr-DLC and N-doped Cr-DLC films were deposited on (100) Si substrates using a hybrid plasma-assisted CVD/PVD process. Film microstructure, composition and chemical state of elements were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Mechanical and tribological properties were investigated using microhardness testing and pin-on-disc experiments. Analysis by TEM and XPS shows that the Cr-DLC films contain a dispersion of amorphous, Cr-rich nanoparticles. In the N-doped films, N combines with C and partly transforms the Cr-rich nanoparticles into chromium carbon nitrides, CrC(N), dispersed in the amorphous DLC matrix. Also, a significant portion of N is incorporated into the C network. The N-doped Cr-DLC films were found to possess higher hardness, lower intrinsic stresses and somewhat higher coefficient of friction and wear rate than Cr-DLC and DLC films. Such influence of the N-doping on the properties is attributed to the formation of CrC(N) nanoparticles and C-N bonds in the DLC matrix.     

Thickness dependence of the structure of diamond-like carbon films by Raman spectroscopy

The thickness dependence on structure of Diamond-like carbon films of a-C:H deposited by ECR-CVD and ta-C by FCVA has been studied by visible and UV Raman spectroscopy. The results show that the evolution of structure as a function of the thickness for a-C:H films contains two stages: when thickness is less than 50 Å, the film contains less sp³ sites and not continuous; and when thickness is up to 50 Å, the film contains more sp³ sites and become continuous. However, for ta-C films, it includes three stages. In the first stage of thickness lower than 20 Å, the film is not continuous, and also contains less sp³. In the second stage of thickness between 20 Å and 50 Å, the sp³ site abruptly shifts a higher value in 20 Å and then keeps stable. In the third stage of thickness over 50 Å, the sp³ site has a little increase and then almost not changed. Thus, the fundamental limitation thickness in using DLC as an ultrathin overcoat for ta-C films is 20 Å (> 10 Å), and for a-C:H films is 50 Å. The implications of result on the mechanisms proposed for the film growth mode were also discussed.     

Effect of metal ion implantation on thermal instability of diamond-like carbon films

In this work, molybdenum and tungsten ions were implanted onto the DLC films deposited by filtered cathodic vacuum arc. We investigated the effects of ion species and doses on carbon related bonding property such as the ratio of sp³ carbon to sp² phase, the chemical composition and tribological properties of the DLC films in the range of 200 to 600 °C. The oxidation starting temperature decreased with an increasing ion dose and ion mass owing to higher sp² carbon fraction. Oxidation of the implanted-metal element, however, keeps the DLC film from carbon sublimation by oxidation, offering stable tribological characteristics by covering it with a metal oxide layer at the high temperature.     

Exploring the potential of high power impulse magnetron sputtering for growth of diamond-like carbon films

Amorphous carbon films are deposited employing high power impulse magnetron sputtering (HiPIMS) at pulsing frequencies of 250 Hz and 1 kHz. Films are also deposited by direct current magnetron sputtering (dcMS), for reference. In both HiPIMS and dcMS cases, unipolar pulsed negative bias voltages up to 150 V are applied to the substrate to tune the energy of the positively charged ions that bombard the growing film. Plasma analysis reveals that HiPIMS leads to generation of a larger number of ions with larger average energies, as compared to dcMS. At the same time, the plasma composition is not affected, with Ar⁺ ions being the dominant ionized species at all deposition conditions. Analysis of the film properties shows that HiPIMS allows for growth of amorphous carbon films with sp³ bond fraction up to 45% and density up to 2.2 g cm^− 3. The corresponding values achieved by dcMS are 30% and 2.05 g cm^− 3, respectively. The larger fraction of sp³ bonds and mass density found in films grown by HiPIMS are explained in light of the more intense ion irradiation provided by the HiPIMS discharge as compared to the dcMS one.     

Liquid phase sintering of functionally graded WC–Co composites

Functionally graded cemented tungsten carbide (WC–Co) is an example of functionally graded materials (FGM) in which mechanical properties are optimized by the presence of microstructural gradients such as cobalt gradient and grain size differences within the microstructure. In particular, a cobalt gradient is preferred. However, the manufacture of FGM WC–Co with a cobalt gradient is difficult because the flow of the liquid phase during liquid phase sintering (LPS) would eliminate any initial cobalt gradient built into the powder compacts. In this paper, different factors, which can be used to influence the migration of liquid during sintering, are investigated. These factors include gradients in grain size, carbon and cobalt content, and sintering time. It is shown that a difference in particle size may induce a step-wise profile of cobalt concentration. Initial carbon content differences, however, can be used to obtain a gradient of cobalt during sintering. The effects of these factors are explained based on the roles of capillary force and phase reactions.     

Friction behaviour of diamond-like carbon films with varying mechanical properties

Diamond-like carbon (DLC) films deposited on silicon wafer with varying film thickness were investigated for their micro-scale friction behaviour. Films with three different thicknesses, namely 100 nm, 500 nm and 1000 nm, deposited by a radio frequency plasma-assisted chemical vapor deposition method on Si (100) wafer, were used as the test samples. The elastic modulus of the DLC samples increased with their film thickness. The micro-scale friction tests were conducted in a ball-on-flat type micro-tribotester, using soda lime glass balls with different radii (0.25 mm, 0.5 mm and 1 mm), and with varying applied normal load (load range: 1500 μN to 4800 μN). Results showed that the friction force increased with applied normal load, whereas with respect to the ball size, two different trends were observed. In the case of 100 nm thick sample, friction increased with the ball size at any given normal load, while for 500 nm and 1000 nm thick samples, friction had an inverse relation with the ball size at all applied normal loads. The friction behaviour in the case of the 100 nm thick film was adhesive in nature, whereas for the thicker films plowing was dominant. The friction behaviour of the test samples with the ball size, which was distinctly different, was discussed in terms of the contact area, influenced by their mechanical property, namely, the elastic modulus.     

A technique for fabrication of coated TiCN-based cermets with functionally graded structure

A technique for fabrication of coated TiCN–Ni–Mo cermets with functionally graded microstructure and composition has been developed. A multilayer coating and the substrate near-surface zone with graded microstructure form as a result of interaction between the cermets and chromium vapour in vacuum. The coating consists of an upper layer of chromium carbide of about 10 μm in thickness and a thin interlayer of less than 1 μm composed of a Ni–Cr alloy between the carbide layer and the substrate. The wide near-surface zone of over 100 μm in thickness with graded microstructure and composition forming under the coatings has an increased Cr content in the Ni-based binder. This zone is characterised by enhanced corrosion- and oxidation-resistance.     

V and N co-doped diamond-like carbon films deposited by pulsed bias arc ion plating

V and N co-doped diamond-like carbon (DLC–VN) composite films were deposited on cemented carbide substrates by pulsed bias arc ion plating. The effects of V and N contents on the structures and properties of the films were investigated by X-ray photoelectron spectroscopy (XPS), Raman spectra, grazing incident X-ray diffraction (GIXRD), transmission electron microscopy (TEM) and nano-indentation, respectively. The as-deposited films consist of a DLC–VN nanocomposite, where VN nanograins are embedded in an amorphous carbon matrix. The V and N contents have significant influences on the relative proportion of VN with respect to DLC. A proper concentration of VN nanocrystals in DLC induces even the formation of nano-diamond. The DLC–VN films have higher hardnesses than pure DLC films, which could be attributed to the nanocomposite structure.     

Thermal fracture resistance of a functionally graded coating with periodic edge cracks

This work investigates the thermal fracture resistance of a functionally graded coating with an array of periodic edge cracks. The integral equation method is used to analyze the thermal stress intensity factors (TSIFs) at the crack tips and the critical thermal shocks that cause crack initiation. The effects of crack density (crack spacing) and thermal property gradients on the critical thermal shocks and TSIFs are examined using an Al₂O₃/Si₃N₄ graded coating on a Si₃N₄ substrate. Numerical results show that for a given crack density, the graded Al₂O₃/Si₃N₄ coating exhibits higher critical thermal shocks than the homogeneous Al₂O₃ coating, and hence higher thermal fracture resistance. For a given material gradation profile, a higher crack density (smaller crack spacing) enhances the critical thermal shock significantly.     

Mechanical properties and antibacterial activity of copper doped diamond-like carbon films

A hydrogenated diamond-like carbon (a-C:H) with a copper dopant (Cu/a-C:H) was deposited on glass substrates using a combined radio-frequency plasma and magnetron sputtering deposition process under various Ar/CH₄ gas mixtures. The effects of the Cu content on the structure and properties of the a-C:H matrix were investigated using X-ray diffraction (XRD), Raman transmission electron microscopy, high-resolution transmission electron microscopy (TEM), and nano-indentation. The bacterial activity of a Cu/a-C:H film was evaluated with Escherichia coli (E. coli). TEM images and XRD spectra demonstrated that composite films containing copper nanoparticles embedded in the a-C:H were deposited on the glass substrates. The Raman spectra showed the structure of a-C:H film was substantially changed by the incorporation of Cu. The Cu/a-C:H films offered superior antibacterial activity against E. coli indicating that they could be suitable for surface coatings in cardiovascular applications.     

Thermal analysis of functionally graded coating AlSi alloy and steel pistons

Functionally graded coatings are coating systems used to increase performances of high temperature components in diesel engines. These coatings consist of a transition from the metallic bond layer to cermet and from cermet to the ceramic layer. In this study, thermal behavior of functional graded coatings on AlSi and steel piston materials was investigated by means of using a commercial code, namely ANSYS. Thermal analyses were employed to deposit metallic, cermet and ceramic powders such as NiCrAl, NiCrAl + MgZrO₃ and MgZrO₃ on the substrate. The numerical results of AlSi and steel pistons are compared with each other. It was shown that the maximum surface temperature of the functional graded coating AlSi alloy and steel pistons was increased by 28% and 17%, respectively.     

掺钨类金刚石膜离子渗硫后的微观结构与摩擦学性能

探讨了掺钨类金刚石(W-DLC)膜沉积及离子渗硫两步合成DLC和WS2复合固体润滑膜的新方法。利用低温离子渗硫技术对4种钨含量的W-DLC膜进行离子渗硫处理,采用扫描电子显微镜(SEM)、俄歇扫描探针(SAM)、X射线光电子能谱(XPS)、拉曼光谱仪(Raman),纳米硬度计(Nano-indenter)和摩擦磨损试验机考察了渗硫处理后W-DLC膜的微观结构与摩擦学性能。结果表明:渗硫处理使W-DLC膜中生成了WS2,促进了DLC膜的石墨化,并降低了其纳米硬度;随钨含量增加,渗硫处理的W-DLC膜纳米硬度逐渐升高,摩擦系数和磨损率逐渐减小,渗硫后的27.7%W-DLC膜表现出最优异的摩擦学性能。     

Fundamentals of liquid phase sintering for modern cermets and functionally graded cemented carbonitrides (FGCC)

Metallurgical reactions and microstructure developments during sintering of modern cermets and functionally graded cemented carbonitrides (FGCC) were investigated by modern analytical methods such as mass spectrometer (MS), differential thermal analysis (DTA), differential scanning calorimeter (DSC), dilatometer (DIL), microscopy and analytical electronic microscopy with energy dispersive spectrometer (EDS). The complex phase reactions and phase equilibria in the multi-component system Ti/Mo/W/Ta/Nb/C,N-Co/Ni were studied. The melting behavior models in the systems of TiC–WC/MoC–Ni/Co, TiC–TiN–WC–Co and TiCN–TaC–WC–Co have been established. By an in-depth understanding of the mechanisms that govern the sintering processing and metallurgical reactions, new cermets and different types of FGCC with desired microstructures and properties were developed.     

Microstructure and tribological properties of diamond-like carbon and TiAlSiCN nanocomposite coatings

Diamond-like carbon (DLC) and TiAlSiCN nanocomposite coatings were synthesized by multi-plasma immersion ion implantation and deposition. The DLC content in the composite coating was controlled by the flow ratio of N₂ to C₂H₂ during the deposition process. The microstructure and tribological properties of the as-deposited coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), nanoindentation and ball-on-disk friction tests. The TEM results show that all the DLC-TiAlSiCN coatings had a two phase composite structure of the TiCN nanocrystals embedded in an amorphous matrix consisting of a-Si₃N₄, a-SiC, a-CN and DLC. TEM observations also reveal that the spacing between the adjacent nanocrystals increases with DLC content. In addition, the DLC-TiAlSiCN nanocomposite coating with a small crystalline spacing of about 0.6 nm shows a higher hardness up to 50 GPa and a larger friction coefficient. An increase in the DLC content of the coating benefits its friction coefficient while its hardness decreases. The friction coefficient reduces to 0.14 when the DLC content is about 31%.     

Ion beam energy effects on structure and properties of SiOx doped diamond-like carbon films

SiO_x doped diamond-like carbon (DLC) films were synthesized by direct ion beam from hexamethyldisiloxane vapor. Effects of ion beam energy were studied. Variation of atomic concentration of the oxygen versus carbon with ion energy has been observed. Raman scattering spectroscopy didn’t indicate essential changes in structure of the films deposited at different ion beam energies. The synthesized films were atomically smooth. Depending on the ion energy the refractive index of the SiO_x doped diamond-like carbon films varied within 2.1-2.5 and increased with increase of energy. The contact angle with water for all samples was only 61-64°.     

氧化物/不锈钢梯度复合材料初步设计与评价

采用粉末层叠和整体热压烧结的方法,制备了Y₂Ti₂O₇/316L不锈钢功能梯度复合材料。经金相显微镜、X射线衍射仪和电子探针分析确定,该材料在金属和氧化物界面处实现了成分和微观组织的梯度过渡。对不同梯度含量复合材料的力学性能测试表明,界面处的力学性能存在相应的梯度变化,即随各层金属相含量的逐渐增加,过渡区材料的致密度、抗弯强度不断提升,而硬度则不断下降。     

Structure, scratch resistance and corrosion performance of nickel doped diamond-like carbon thin films

Nickel doped diamond-like carbon (DLC:Ni) thin films were fabricated on conductive p-Si (100) substrates with DC magnetron sputtering deposition by varying DC power applied to a Ni target. The bonding structure, surface morphology, scratch resistance and corrosion resistance of the DLC:Ni films were studied using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM), micro-scratch test, potentiodynamic polarization test and open circuit potential measurement. The results indicated that the corrosion resistance of the DLC:Ni films in a 0.6 M NaCl solution decreased with increased Ni content in the films though the films showed good passivation behavior in the NaCl solution.     

Modification of diamond-like carbon coatings with fluorine to reduce biofouling adhesion

Diamond-like carbon (DLC) and fluorinated DLC (F-DLC) coatings were deposited onto 10 mm stainless steel 316 L discs by radio frequency plasma-enhanced chemical vapour deposition (rf PECVD). Surface energy analysis of the F-DLC coatings revealed that with increasing F content the total surface energy decreased significantly, which was attributed to the change of the bonding nature in the coatings, in particularly increasing CF and CF₂ bonds. The anti-biofouling property of F-DLC coatings was evaluated with Pseudomonas fluorescens, which is one of the most common bacteria forming biofilms on the surface of heat exchangers in cooling water systems. The experimental results showed that the incorporation of fluorine into the DLC coatings reduced bacterial attachment and increased bacterial removal. The F-DLC coatings with higher F content (39.2 at.%) reduced bacterial attachment by 48.8% and increased removal by 90.2%, compared with a standard DLC coating.