Shuichi Watanabe

The synthesis of cubic BN films using a hot cathode plasma discharge in a parallel magnetic field

Abstract A method of synthesizing cubic boron nitride (c-BN) films by the activated reactive evaporation process was investigated. A special feature of the gas activation process is that a hot cathode plasma discharge in a parallel magnetic field is used. A conventional type of ion plating apparatus, with an electron beam gun for the evaporation of boron, was used to synthesize c-BN films on a single-crystal silicon plate. A stoichiometric boron nitride film was obtained by reacting boron vapour with high density nitrogen ions, prepared using a hot cathode plasma discharge in a parallel magnetic field around the substrate. Argon gas was mixed with the reactant nitrogen gas to enhance BN formation. An r.f. bias potential was applied to the substrate in order to obtain the cubic BN phase. The optimum value of the total gas pressure in the evaporation chamber was in the range 2.6 × 10 -2 -1.1 × 10 -1 Pa. The structures of the films obtained were characterized using IR absorption spectroscopy and X-ray diffraction analysis.

THE POSSIBILITY OF COATING CUBIC BN FILMS ON VARIOUS SUBSTRATES

Abstract A cubic BN (c-BN) film with stoichiometric composition has been prepared on a silicon wafer using a hot cathode plasma discharge in a parallel magnetic field. However, the film does not show good adhesion because of internal stress. The effect of variation in nitrogen concentration across the film thickness on adhesion has been examined to attempt to produce good adhesion of the film on a silicon wafer. A stainless steel substrate was also used. In this case it was necessary to use a dual layer deposition technique in which a titanium base layer or first layer was deposited followed by a second layer of graded BN (nitrogen concentration varied across the film thickness). The same idea was then applied to more practical tool materials, i.e. WC-Co alloy and high speed steel; these two materials were also successfully deposited with c-BN with good adhesion by using a first layer of titanium. Furthermore, it was observed that, for a silicon substrate with a diamond coating, a c-BN film could be directly deposited on the substrate without using the graded BN layers or the interlayer of titanium.

CVD diamond, DLC, and c‐BN coatings for solid film lubrication

The main criteria for judging coating performance were coefficient of friction and wear rate, which had to be less than 0.1 and 10-6 mm3/(N.m), respectively. Carbon‐ and nitrogen‐ion‐implanted, fine‐grain, chemical‐vapor‐deposited (CVD) diamond and diamondlike carbon (DLC) ion beam deposited on fine‐grain CVD diamond met the criteria regardless of environment (vacuum, nitrogen, and air).

Thermal Stability and Tribological Performance of DLC-Si–O Films

The thermal stability and tribological performance of silicon- and oxygen-incorporated diamond-like carbon films were investigated. The DLC-Si-O films were deposited using plasma-based ion implantation (PBII) method. The deposited films were annealed at 400°C, 600°C, and 750°C for 1 hour in vacuum, in argon, and in air atmospheres. Film properties were investigated using the Fourier transforms infrared spectroscopy, Raman spectroscopy, energy dispersive X-ray spectroscopy, and a ball-on-disk friction tester. The structures of the DLC-Si-O films with a low Si content ( ≤ 25 at.%Si, ≤ 1 at.%O) and high Si content ( > 25 at.%Si, > 1 at.%O) were not affected by the thermal annealing in vacuum at 400°C and 600°C, respectively, while they were affected by thermal annealing in argon and in air at 400°C. Film with 34 at.%Si and 9 at.%O after annealing demonstrated almost constant atomic contents until annealing at 600°C in vacuum. The friction coefficient of DLC-Si–O films with 34 at.%Si and 9 at.%O was shown to be relatively stable, with a friction coefficient of 0.04 before annealing and 0.05 after annealing at 600°C in vacuum. Moreover, the low friction coefficient of film annealed at 600°C in vacuum with 34 at.%Si and 9 at.%O was corresponded with low wear rate of 1.85 × 10 −7 mm 3/Nm.

Low-Friction and Long-Life Solid Lubricant Films Structured of Nanoperiod Tungsten Disulfide and Molybdenum Disulfide Multilayer

To reduce friction coefficient, hardness is increased by using a nanometer-period multilayer structure and shearing strength is decreased by applying of low-shearing-strength tungsten disulfide and molybdenum disulfide layers. In nanoindentation testing, multilayer films showed a higher hardness and a lower modulus of dissipation energy than single-layer films. In nanoscratch and microwear testing using an atomic force microscope (AFM), both the scratching force and wear rate of multilayer films could be decreased. The friction coefficient of the nanoperiod multilayer film was as low as µ=0.04 in the ball-on-disk tribotest in 52 to 58% humidity conditions. The friction endurance life of the nanoperiod multilayer films evaluated from the cycles in which the friction coefficient increases rapidly is nine times longer than those of single-layer films.

Optical properties of cubic boron nitride films made by a reactive ion plating method

Abstract Cubic boron nitride (c-BN) has been prepared using a magnetically enhanced plasma ion plating method. A magnetic field parallel to the electric field is used in conjunction with a hot cathode to produce a plasma at low pressure. R.f. power was simultaneously applied to the substrate holder to provide a negative bias for the desired ion bombardment. The optical properties of the c-BN films from the UV through the visible to near-IR were measured in comparison with hexagonal BN, mixed-phase BN and amorphous BN prepared in the same apparatus under different conditions, using a double-monochromator spectrophotometer. The crystal structures of these films were identified by electron diffraction analysis. It was found that c-BN films deposited on quartz substrates have the highest optical transparency, as well as the shortest wavelength above which they are transparent.

The Comparison of Biocompatibility Properties between Ti Alloys and Fluorinated Diamond-Like Carbon Films

Titanium and titanium alloys have found several applications in the biomedical field due to their unique biocompatibility. However, there are problems associated with these materials in applications in which there is direct contact with blood, for instance, thrombogenesis and protein adsorption. Surface modification is one of the effective methods used to improve the performance of Ti and Ti alloys in these circumstances. In this study, fluorinated diamond-like carbon (F-DLC) films are chosen to take into account the biocompatible properties compared with Ti alloys. F-DLC films were prepared on NiTi substrates by a plasma-based ion implantation (PBII) technique using acetylene (C2H2) and tetrafluoromethane (CF4) as plasma sources. The structure of the films was characterized by Raman spectroscopy. The contact angle and surface energy were also measured. Protein adsorption was performed by treating the films with bovine serum albumin and fibrinogen. The electrochemical corrosion behavior was investigated in Hanks’ solution by means of a potentiodynamic polarization technique. Cytotoxicity tests were performed using MTT assay and dyed fluorescence. The results indicate that F-DLC films present their hydrophobic surfaces due to a high contact angle and low surface energy. These films can support the higher albumin-to-fibrinogen ratio as compared to Ti alloys. They tend to suppress the platelet adhesion. Furthermore, F-DLC films exhibit better corrosion resistance and less cytotoxicity on their surfaces. It can be concluded that F-DLC films can improve the biocompatibility properties of Ti alloys.

Tribological Behavior of Cubic Boron Nitride Film Sliding Against Diamond

Cubic boron nitride (c-BN) film was deposited onto a silicon substrate by means of a magnetically enhanced plasma ion plating method utilizing a hot cathode plasma discharge in parallel magnetic field. In this study, the friction and wear behaviors of the c-BN film, particularly when it came into sliding contact with diamond, were investigated using a reciprocating tribometer in an applied normal load range of 0.1 ~ 4.9 N. The results showed that the friction coefficient of the c-BN film sliding against the diamond indenter tended to decrease as the load increased, and was very low, exhibiting values of 0.03 ~ 0.065 at the maximum load of 4.9 N. Furthermore, the study confirmed that the friction coefficient of annealed c-BN film was lower than that of as-deposited c-BN film throughout the whole load range. Judging from the results of comparable investigations in which c-BN film came into contact with other materials such as c-BN compact, SiC and stainless steel, the wear performance and peeling resistance of the c-BN film proved to be significantly better in the case of contact with diamond.

Effects of N+ ion implantation into cubic BN film for tribological usages

Abstract Cubic boron nitride (c-BN) film was deposited onto a silicon substrate by means of the magnetically enhanced ion-plating method developed by the authors, and ion implantation was performed as a post-treatment using N + under various conditions. In this study, the crystal structure and tribological properties against diamond of the c-BN film treated by ion implantation were investigated. The results showed that implantation depth increased with an increase in implanting energy even on this c-BN, and it was found that ion damage to the c-BN phase was less when the dosage fell below 8 × 10 15 ions cm -2 . It was also found that ion implantation was effective in decreasing the friction coefficient when the treated film was contacted with diamond.

Deposition and Tribological Properties of Sulfur-Doped DLC Films Deposited by PBII Method

Sulfur-doped diamond-like carbon films (S-DLC) fabricated from and mixtures were used to study the effects of sulfur content and negative pulse bias voltage on the deposition and tribological properties of films prepared by plasma-based ion implantation (PBII). The structure and relative concentration of the films were analyzed by Raman spectroscopy and Auger electron spectroscopy. Hardness and elastic modulus of films were measured by nanoindentation hardness testing. Tribological characteristics of films were performed using a ball-on-disk friction tester. The results indicate that with the increasing sulfur content, the hardness and elastic modulus decrease. Additionally, by changing the negative pulse bias voltage from 0 kV to 5 kV, the hardness and elastic modulus increase, while the friction coefficient and specific wear rate tends to decrease. Moreover, at a negative pulse bias voltage of 5 kV and flow-rate ratio of 1 : 2, there is considerable improvement in friction coefficient of 0.05 under ambient air is due to the formation of a transfer films on the interface. The decrease in the friction coefficient of films doped with 4.9 at.% sulfur is greater under high vacuum (0.03) than under ambient air (>0.1).