Presents the study on thermal stability of diamond -like carbon (DLC) films and measurements of thermal stability and the analysis of the variation of structure and intrinsic stress for DLC films vs annealing temperature and reviews the recent progress on thermal stability of DLC films.

The frictional behaviors of DLC films against bearing steel balls and Si3N4 balls in different humid air and vacuum environments were investigated. The results show that the friction coefficients of DLC films against bearing steel balls in steady-state decrease from 0.34 to 0.12 with the increase in the relative humidity (RH) of air from 10 to 95%, respectively, while the friction coefficients of DLC films against the Si3N4 balls increase from 0.02 to 0.12 with the increase in the RH of air from 10 to 95%. Both the friction coefficients of DLC films against the bearing steel balls and against Si3N4 balls become gradually close to each other with the increase in the RH of air and are all the same to 0.12 when the RH up to 95%. In vacuum, the friction coefficient of DLC film against DLC film (which is deposited on the bearing steel ball) is the lowest and only about 0.05; the friction coefficients of DLC films against bearing steel balls is about 0.12 and lower than that of in dry air and humid air, while the friction coefficients of DLC films against Si3N4 balls is about 0.1 and higher than that of in dry air but lower than in humid air a little. The variation of the friction coefficients of DLC films against both bearing steel balls and Si3N4 balls with the increase in different RH of air is associated with the formation of the transfer film and partial graphitized DLC films. The friction coefficients of DLC films against bearing steel balls in dry air exhibited higher lever; perhaps related with the oxidization of DLC films and steel counterpart during sliding in dry air. The friction coefficient of DLC films against Si3N4 balls in vacuum higher than in dry air is due to the dehydrogenation and the graphitizing of the DLC film under the action of friction stress, besides, the hydrogen content in DLC films prepared in this study is only 26.7at.%. This hydrogen content is lower than ordinal a-C:H films; this probably weakened the oxidization for DLC films during sliding in dry and humid air, thereby decreasing the friction coefficient.

Cubic boron nitride (c-BN) films were deposited on Si substrate with poor adhesion using magnetically enhanced active reaction evaporation (ME-ARE). An attempt has been made to enhance the adhesion strength between c-BN film and substrate by nitrogen plasma based ion implantation (PBII) into c-BN film. Nitrogen ion doses range from 5×1016 to 1×1017 ions cm−2 at an implant voltage of 50 kV. The nitrogen ion implanted c-BN films were analyzed using FTIR, scratch test, and XPS to investigate the change of structure, adhesion strength of c-BN film, and interfacial mixing between the initial turbostratic BN (t-BN) film layer and substrate caused by nitrogen ion implantation. FTIR spectra showed little change of c-BN phase content in the films under the above implantation conditions but XPS depth elemental profile of N+-implanted boron nitride films displayed a mixed layer consisting of elements from film and substrate formed at interface. A highly optimized dynamic Monte Carlo program TAMIX was used to simulate the PBII process in a good agreement with above measured depth elemental profile. The scratch test showed that the adhesion strength evaluated in terms of the critical load of N+-implanted c-BN film was 1.4 times higher than that of as deposited c-BM film.

The effect of negative bias pulse applied to substrate on the bonding configurations and properties of diamond-like carbon (DLC) films prepared by plasma-based ion implantation (PBII) with acetylene were investigated. The research results show that as the plasma density is 109 cm−3 and the negative bias pulses applied to substrate decrease from 50 to 10 kV, the Raman spectra of the carbon films all possess the most dominant characterizations of typical a-C:H [J. Robertson, Mater. Sci. Eng., R 37 (2002) 129-281.], the positions and FWHM for G and D peaks vary no distinguished, but the ratio ID/IG decreases monotonically, as the negative bias pulse decreasing to 5 kV, the Raman spectrum possesses rather strong photoluminescence characterized the polymer-like phase. The variation of Raman spectra for plasma density 108 cm−3 is analogous to that of the plasma density 109 cm−3. The binding energies of XPS C1s peak decrease from the side of diamond peak to the side of graphite peak with the increasing of negative bias pulse from 10 to 50 kV monotonously, the sp3 content in the films increases with the decreasing in the negative bias pulse. With the increasing of negative bias pulse from 0 to 50 kV, the surface electric resistance of the films decreases monotonously, but the surface nanohardness at first increases with the increasing of the negative bias pulse from 0 to 10 kV, then decreases with the increasing of the negative bias pulse from 10 to 50 kV monotonously. These properties of the films are corresponding to the bonding configurations of the films. The reason for the highest sp3 fractions of the a-C:H films formed at higher effective ion energy per C atom in PBII is discussed in this paper.

A prismoidal-shaped target with trapezoidal section containing four different convex corners was implanted with nitrogen using plasma-based ion implantation (PBII) in order to study the effect of target shape on the retained dose and its distribution with depth. Nitrogen was implanted into a silicon wafer clamped on the side wall of the sample holder, and Auger electron spectroscopy was employed to obtain the nitrogen depth distribution and the retained dose. Both a former simulation and the present experimental analysis exhibit dependence of the dose on the target shape but with a reversed trend. A method that combines a fluid dynamic model to simulate plasma sheath expansion during a high voltage pulse and the Monte Carlo method of the TRIM code to simulate the incident ion distribution in the solid was presented to predict the concentration depth profile after PBII. When establishing the model, the mechanism of the resulting lower retained dose near the corner with the higher density of ion impact flux was discussed. It was found that the oblique impact of the ion flux reduces the retained dose of the modified layer in three ways and changes the form of the profile remarkably. The continuous distribution of ion impact energy and the low N+/N-2 ratio in the plasma shift the N depth profile nearer to the surface, which reduces the implantation depth significantly. In addition, the oblique impact near the edge of the convex corner decreases the reduction in ion range and retained dose and should account for the gradient in the retained dose distribution on the target surface. The model presented can give a good prediction and explanation for the experimental results.

DLC coated 2024 aluminum alloy samples having four different intermediate layers prepared by different plasma-based ion implantation modes. The composition and structures of DLC coated samples were investigated by X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy and glancing angle X-ray diffraction (GXRD). Knoop micro-hardness and nano-hardness of the layers had been measured too. The tribological behaviors of these samples were investigated by ball on disk frictional tester and scanning electron microscopy (SEM). Results show that the stable friction coefficients of these four samples are nearly same and about 0.1, but the sliding cycles of holding stable friction coefficient are different, they increase according to the order of samples (a)–(d) sequentially. For these four samples, whether the loading was 1 or 20N, the stable friction coefficient is nearly same, but the sliding cycles of holding stable friction coefficient are different, while the cycles of holding stable friction coefficient as loading 20N are less than as loading 1N for same sample. The wear rate of the samples decreases according to the order of samples (a)–(d) sequentially. The SEM morphologies of the worn tracks are dependent on the intermediate layer structures and friction test conditions, the characters of the wear are rubbing, abrasive wear and delamination wear, but for samples (a) and (b) a slight adhesive wear appears as loading 20N.

Using plasma-based ion implantation, two types of gradient layers have been prepared on 2024 Al alloy. One is prepared by N-implantation then C-deposition, the other adds an interlayer composed of a Ti layer and a Ti–N layer between N-implantation and C-deposition. C-deposition is carried out at various implanting voltages or C2H2/H2 ratios. The composition depth profiles of these layers were characterized by x-ray photoelectron spectroscopy. The structure, morphologies and microstructure of the C layers were studied using Raman spectroscopy, atomic force microscope and transmission electron microscope, respectively. The surface hardness was measured with a Knoop tester and a mechanical property microprobe. The dry ball-on-disc wear tests were performed in ambient air. The gradient layer without interlayer is composed of an N-implanted layer rich in AlN and a diamond-like carbon (DLC) layer (film), and the two layers are connected with a C–Al transition layer containing Al4C3. The Ti layer rich in α -Ti and the N-implanted layer are connected by a Ti–Al transition layer containing TiAl3, while the Ti–N layer rich in TiN and the DLC film are connected by a C–Ti transition layer containing TiC, TiCN, etc. Thus, the gradient layer with interlayers has optimized the gradient structure. DLC films are compact and amorphous, contain high sp3/sp2 ratios and depend on the implanting voltage and the C2H2/H2 ratio. Similarly, these gradient layers exhibit significant improvement in morphologies, surface hardness and tribological properties; the interlayer, the implanting voltage and the C2H2/H2 ratio all have prominent effects on these properties.

Al-plasma based ion implantation (Al-PBII) into AgMgNi alloy is carried out using metal plasma generated from the unbalanced magnetron sputtering (UBMS) and RF stimulating. The depth profile and the chemical states of Al and O are analyzed using XPS. The phase structures of the samples before and after the implantation are determined by XRD analysis. The results show that an Al implantation layer appears on the surface of AgMgNi alloy substrates and the concentration of Al decreases gradually as the depth increases. There are three chemical states of Al in the implantation layer: pure Al, Al in solid solution and as Al2O3 and two chemical states of oxygen, i.e. solid solved oxygen and oxygen in Al2O3. The effect of the distance from magnetron target to substrates (Ds−t) on the surface structure has also been studied. Comparing the surface structures before and after implantation shows that: with a shorter Ds−t of 200 mm, the lattice constant α of the Ag phase in the implantation layer of AgMgNi alloy substrate decreases, while the intensity of the peak defined as the (311) plane increases; when Ds−t is increased to 300 mm, the lattice constant α increases with no significant change of the intensity of the peak of any plane. At a moderate Ds−t of 250 mm, no significant change of α can be detected, but the intensity of the peak defined as (311) increases. The reason for the changes of the surface structure of AgMgNi alloy is the formation of an Ag–Al implantation layer and the collision cascades of Ar+ in the surface of the substrate.

As an interlayer in the gradient layers such as AlN/Ti/TiN/DLC prepared by plasma-based ion implantation (PBII) on 2024 aluminum alloy, titanium layer plays an important role in enhancing adhesion, reducing thermal stress, limiting the crack propagation, etc. A series of dual-layers prepared by PBII with nitrogen then titanium at various sputtering currents of titanium target on 2024 aluminum alloy have been reported in this paper. The composition distributions and the chemical states are analyzed using X-ray photoelectron spectroscopy (XPS). The structures are studied with grazing X-ray diffraction (GXRD). The results show that PBII with titanium strongly depends on the sputtering current. It is found that there exists a critical sputtering current corresponding only to a titanium-implanted layer containing TiAl3. When the sputtering current exceeds the critical value, a titanium-deposited layer rich in α-Ti is formed on a titanium-implanted layer. By controlling the sputtering current an appropriate titanium interlayer can be prepared to meet the requirement of forming a proper gradient layer.

The structures of diamond-like carbon (DLC) films deposited by vacuum arc evaporation with and without curve arc magnetic filter are studied and compared using Raman shifts. The Raman shifts are deconvolved into D peak and G peak with Gaussian-Lorentzion fitness. The effects of the deposition parameters such as bias voltage and bias current strength of curved magnetic fields on the DLC films structures are discussed. The results show that Ar gas pressure has not obvious effect on the formation of the DLC film; moderate bias current increases the sp3 content; the sp2 cluster can be increased for a too high substrate bias. The magnetic curved filter not only can remove the carbon macroparticles, but also can improve the sp3 content.

Plasma base ion implantation (PBII) at elevated temperature is a very important technology for the surface modification of materials. A technology for PBII at constant temperature is presented. The single implantation parameter such as implantation dose, implantation voltage and temperature can be changed conveniently using the technology, which provide a doable technology for the optimization of ion implantation. N ion implantation into αFe is carried out using the technology at various temperatures, and the results indicate that the temperature or voltage can be changed singly in larger range on the bases of designed technology during ion implantation. The fluctuation of temperature is very small, and the nitride layer thickness can be increased greatly.

2024 aluminum alloy was implanted with nitrogen then titanium at different titanium target sputtering currents by plasma-based ion implantation (PBII). The appearances were observed by atomic force microscope, and the surface hardness was measured with Knoop hardness tester and the mechanical property microprobe. Ball-on-disc dry wear experiments were performed under ambient air conditions, to study the tribological properties of the modified layers against GCr15 steel ball, employing various loads and a constant sliding speed. After dual modifications, surface hardness at 100 nm depth could reach to 9 GPa, increasing by about 5 times; tribological properties at lower load(e. g. 1 N) were obviously improved, with the friction coefficient(below 0.2) decreasing by over 60%, and the wear life(800 times) increasing by about 5 times. Meanwhile, with the increase of the sputtering current the appearance is smooth, the surface hardness tends to a slow and even variation, the wear life presents a parabola-like change, and the friction coefficient and the adhesive wear degree decrease. However, tribological properties are reduced with the increase of the load due to the modified layer rapidly getting thin.

Carbon nitride films have been grown by vacuum cathodic arc method in the substrate temperature range of 100–500 °C. The bonding structure of the films was investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and infrared (IR) spectroscopy. With increasing substrate temperature, the films indicate various characteristics. At 100 °C, it can be described as a network similar to DLC in which aromatic sp2C phase is cross-linked by sp3C phase. Between 200 and 400 °C, with increasing substrate temperature the films become graphitized and the sp2CN phase increases, meanwhile the non-aromatic sp2CN phase appears at the edges of aromatic clusters in planar position as well as in out-of-planar regions. While at 500 °C the non-aromatic sp2CN phase almost comes to the same level as the aromatic sp2CN phase. So in the network of the film the aromatic sp2C phase is cross-linked by the non-aromatic sp2C phase. Based on the variation of the microstructure of the films, a comprehensive assignment pattern for the XPS C1s and N1s at different substrate temperature is proposed. In addition, the interpretation of p electron band in valence band spectra at various substrate temperatures is also discussed.

The retained dose and compositional depth profile were studied in the context of cylindrical target with different plasma density treated by plasma-based ion implantation (PBII). Nitrogen was implanted into silicon wafer clamped on the samples in order to acquire high quality profiles. Auger electron spectroscopy (AES) was used to acquire the nitrogen depth profile at the middle of Si wafer. A method, that combined fluid dynamic model to simulate plasma sheath expansion during high voltage pulse and TRIM code to simulate incident ion distribution in the solid was presented to simulate the experimental results. Both retained dose and N depth profile were compared with the results of theoretical simulation. The agreement between them for all three cases is good; that is, the model can give a good prediction and explanation to the experimental results. The retained dose for cylinder increases with increasing plasma density. The continuously distributed energy of incident ions and low N+/N2 ratio in the plasma shift the N depth profile nearer to the surface and reduce the range significantly.

TiAlN/Ti coating was deposited by multiarc ion plating (MAIP) method with hotpresssintered TiAl alloy used as the target. The interface structure of coating was studied with XTEM. The results show that both TiAlN layer and Ti layer have polycrystalline columnar structure, an interface phase FeTi, which exists between the Ti transition layer and the high speed steel (HSS) substrate has certain orientation relationship with the αFe phase in the substrate.

The composition depth profiles, structure and ball-on-disk frictional characteristics of aluminum alloys 2024 plasma-based ion implanted with nitrogen, titanium and nitrogen then acetylene were investigated. The layers implanted with nitrogen then with nitrogen and titanium and finally with acetylene included three zones: a top DLC (diamond-like carbon) zone, a C, Ti and N coexisting intermediate zone which undergoes chemical changes forming TiC, Ti(C,N), TiN (Ti,Al)N and AlN second phases, and the bottom zone of the substrate. The micro-hardness and nano-hardness of these layers are HK7.8 GPa and 22 GPa, respectively. The layers showed lower friction coefficient and higher wear resistance. The Raman spectra for worn tracks after sliding for different numbers of cycles showed that when the loading was I N after sliding 10,000 cycles, a slight graphitization phenomenon of the DLC film is found. If the loading was 20 N, the graphitization phenomenon of the DLC film is more obvious after sliding 2000 cycles. The SEM morphologies of the wear tracks showed that when the load was 1 N, after sliding 7200 cycles the wear is from rubbing and abrasive wear. When the load was 20 N, after sliding 2000 cycles, delamination wear is dominant.

Based on plasma source ion implantation with nitrogen, 2024 aluminum alloy (LY12) was further implanted with titanium plus nitrogen, or with titanium plus nitrogen and titanium, to generate the intermediate layers of different compositions and thickness, followed by implantation with carbon to generate DLC films on the intermediate layers. The composition depth distributions of the modified layers were characterized using X-ray photoelectron spectroscopy. The nano-hardness and the friction and wear behavior of the DLC films were examined, while the effect of the intermediate layer composition and structure on the tribological properties of the DLC films against steel was discussed. Results showed that the carbon-implanted layer was composed of DCL films whose properties were closely related to the composition and structure of the intermediate layers. The DLC films on various intermediate layers showed much higher nanohardness and better wear resistance than the ones without the intermediate layer. Moreover, the implanted carbon reacted chemically with the elements in the intermediate layer, which contributed to increasing the interfacial bonding strength between various gradient layers. Thus the DLC films with optimized tribological behavior could be prepared by properly screening the intermediate layer which affected the appearances, thickness and structures of the carbon-implanted modified layers. In this sense, the DLC film on the intermediate layer after the implantation with titanium, nitrogen and titanium showed the best wear resistance.

This paper reports the research that systematically studied the effect of the adjustable process parameters on the retained dose in plasma based ion implantation with an aim to provide a method for optimizing the implantation process. Nitrogen was implanted in a silicon wafer clamped on a cylindrical sample holder while varying parameters such as implantation voltage, radio frequency (RF) power, pulse width and target size. Auger electron spectroscopy was used to execute sputter depth profiling and to obtain the retained dose at the middle of the silicon wafer. The retained dose on the wafer was also predicted using fluid dynamic model, which simulates the sheath dynamic mode with consideration of the sputtering effect of the implanted ions. The measured results were compared with theoretical calculations, and the agreement for all the samples was good. The implantation dose for the cylinder will increase with increasing implantation voltage, pulse width or the RF power. A larger sample will result in a decreased dose, although the large ion reception area will push the sheath edge to a further position from the substrate.

The effects of thermal annealing on the component and microstructure of carbon nitride films deposited by vacuum cathodic arc method are reported. The bonding structure of the films is investigated by Raman spectroscopy, FTIR, XPS and valence band XPS. Upon annealing, the N content of the film drops gradually from original 31.0 to 17.0at.% at 600°C. The results of Raman spectroscopy, FTIR and valence XPS demonstrate that the films below 500°C mainly consist of aromatic cluster component and polymeric component, which is rather stable upon the increasing of anealing temperatures. With the further increasing of the annealing temperatures from 400 to 600°C, the fraction of polymeric component decreases and the aromatic component develops greatly. Meanwhile the films tend to transform towards the fullerene-like microstructure, which can be seen from the large separation of the N 1s peaks (>2.0eV). As a result the N sp3 C bonds increase due to the rising of cross-linking between the graphite plane.