Hisanori Ohara

An investigation of the wear track on DLC (a-C:H) film by time-of-flight secondary ion mass spectroscopy

Abstract Tribological behaviors of diamond-like carbon (DLC) on steel under ambient air without lubricant were investigated. DLC (a-C:H) film was prepared on a cemented carbide substrate by radio frequency (r.f.) plasma assisted chemical vapor deposition (PACVD) using a methane (CH 4 ) precursor. The hydrogen content in DLC film was approximately 35 at.%. Pin-on-disk experiments were conducted on DLC-coated disk at the sliding velocity of 52 mm/s under 10 N loading using a steel ball (AISI 52100, 6 mm in diameter) as the pin material. After the evaluation of friction coefficient and wear resistance, the transferred layer and wear debris on the wear track of DLC film were investigated using Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). The data of TOF-SIMS show the existence of hydrocarbon macromolecules (C n H m ) inside the wear track. This result suggests there is a formation of some kind of lubricant materials containing polymer (macromolecule of hydrocarbon), which is generated by the polymerization of DLC film during the tribo-test, contributing thus, to the low friction performance of DLC film.

Thermal stability of TiN/AlN superlattices

Abstract In this paper, the thermal study of a TiN/AlN superlattice was reported. The thermal stability of a superlattice structure and a crystal structure of cubic AlN in a TiN/AlN superlattice were evaluated by using in situ high temperature transmission electron microscopy (HTTEM), X-ray diffraction (XRD) measurements and TEM observations after an annealing treatment in a hydrogen atmosphere, and semi in situ high temperature X-ray diffraction (HTXRD) in a nitrogen atmosphere. It was confirmed that the superlattice structure remained up to 1473 K for a short time by HTTEM observation. HTXRD studies showed that the superlattice structure and c-AlN remained after 1273 K annealing for 3.5 h. According to the change of low angle diffraction intensity of HTXRD, two kinds of diffusion processes may operate. One was short range diffusion that improved the superlattice structure from 1073–1233 K and the other was long range diffusion that started at above 1233 K.

Deposition of NiTiN nano-composite films by cathodic arc ion-plating

Abstract Thick composite films containing Ni and TiN were prepared by using the filtered cathodic arc ion-plating method. In this study, Ni and Ti were simulataneously evaporated by vacuum arc discharge in a nitrogen atmosphere. Since a magnetic field in a filtered arc-evaporator transports only small size ionized particles to the substrate, macro-particles are eliminated from the film and a uniform fine structure can be obtained. It was observed by transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD) that Ni and TiN particles with 5–10 nm diameter were deposited. Scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX) were also used to investigate the morphology and the composition of films. Residual stresses were evaluated by measuring the bending of the substrate before and after the deposition. Hardness measurements were also carried out to investigate the mechanical properties of films. The hardness of the film increased with the increase in the TiN content of the film. When the Ni content was lower than 30 at%, the hardness of the film was nearly the same as TiN itself. The residual stresses of the Ni rich films were 0.05–0.5 GPa (tensile stresses) and those of the TiN rich films were −1–−3 GPa (compressive stresses). Substrate bias voltage and N 2 pressure had a great effect on the residual stress. The compositionally graded multi-layered films (thickness of 350 μm) were synthesized from these results.

Characterization of ion implanted TiN films

Abstract The tribological properties, chemical states, and microstructures of TiN films implanted with Cr and Al ions have been studied. TiN films were deposited using the cathodic arc ion-plating method. After the deposition, Cr or Al ions were implanted into TiN films at an energy below 200 keV. The wear resistance of the ion implanted TiN films, measured by the pin-on-disk method, was improved when compared to the as-deposited TiN film. The XPS spectrum of the implanted films showed the components of CrN and AlN bonds respectively. The glancing angle X-ray diffraction analysis indicated the formation of a ternary compound of TiCrN or TiAlN. Some mechanisms of the tribological improvements by ion implantation are discussed.

The production and properties of TiN-Ni nanostructure films by filtered vacuum arc deposition

Abstract Nanostructure films, consisting of TiN and Ni, were obtained by filtered vacuum arc deposition. The TiN-Ni nanostructure film is expected to have superior mechanical properties. In this method, Ti metal ions and Ni metal ions were alternately introduced to the substrate along a magnetic field sustained in the quarter-torus. The nanoparticle structure and the multilayer structure could be obtained. The TED pattern indicated that the crystallographic orientations of TiN and Ni were aligned, TiN(111) //Ni(111), TiN(100) //Ni (100). The thermal stability of the nanostructure and the film hardness were investigated up to 1053 K. It was confirmed that the nanostructure and the film hardness were stable up to 973 K. The nanostructure was effective for improvement of hardness.

Characterization of TiN films alternately treated with PVD and Cr ion implantation

Abstract The projected ranges of the conventional ion implantation are generally below submicrons. This makes it difficult to apply the implantation techniques to the tribological uses. The combined process of the physical vapor deposition (PVD) and the ion implantation was developed to form the thick implanted layers over a few microns. In this process, firstly, the PVD films are deposited by the cathodic arc ion plating method with a film thickness of 50 to 250 nm. Secondly, the metal ions are implanted using the pulsed arc ion source at an energy below 80 keV without mass separation. These two processes were alternately conducted up to the film thickness of a few microns. Using this combined process, Cr implanted PVD-TiN films were studied. The film thicknesses of the implanted layers were 2–7 μm, which are over ten times larger than those of conventionally implanted layers. Furthermore, these films showed excellent wear resistances compared with the unimplanted PVD-TiN films.

CVD Tungsten and Tungsten-Rhenium Alloys for Structural Applications

Abstract The microstructures of CVD tungsten and tungsten-rhenium alloys have been investigated to evaluate their suitability as high temperature materials. We found that the partial pressure in the reaction chamber affected the microstructure and surface roughness of deposited pure tungsten and tungsten-rhenium alloys. Grain sizes smaller than 0.5 im were obtained for both deposited pure tungsten and tungsten-rhenium alloys. Fine-grained tungsten proved to have greater hardness (Hv>1000 at room temperature (R.T.)) bending strength (δ = 700-1230 MPa at R.T.-l 175 K) and thermal coefficient of linear expansion (β = 4.5-4.9 xl06K−1 at 575-1175 K) characteristics than tungsten with columnar structure.