Kaoru Awazu

A study of cavitation bubble collapse pressures and erosion part 1: A method for measurement of collapse pressures

Abstract A method for measuring the distribution of the pressures at collapse in caviation bubbles, and a data acquisition system, were studied in a magnetostrictive vibratory test. Impact loads (collapse pressures) were measured by our specially developed method using a pressure detector with a piezoelectric ceramic. The distribution curves for the impact loads were compared with those for the erosion pit sizes occurring at an early stage on the surfaces of aluminium, copper and mild steel. Assuming that an individual pit is formed by a single pulse from a collapsing bubble, the impact loads necessary to form a pit 4 μm in diameter were found to be 9.1 N, 9.7 N and 13.7 N for aluminium, copper and mild steel respectively. The number of impact loads larger than that required for the initiation of an erosion pit was found to be very small.

Adhesion strength of DLC films on glass with mixing layer prepared by IBAD

Abstract The improvement of the adhesion of diamond-like carbon (DLC) films has been tried by ion beam assisted deposition (IBAD). The adhesion strength must be quantitatively evaluated and determined in order to confirm the improving effect of the adhesion of DLC films by IBAD. In this study, DLC films were prepared on a glass substrate with a mixing layer prepared by IBAD. For the samples, the scratch tests were carried out using a scratch tester with a CCD camera and two AE sensors. The detachment process of the DLC film during a scratch test was observed and the detachment area was measured. On the other hand, AE signals were detected corresponding to the detachment of the DLC film, and the force causing the detachment was determined by analyzing the signals. The adhesion strength of DLC films was calculated from the detachment area and the force. From that result, the adhesion strength of DLC films without a mixing layer was 3.2 MPa. When the mixing layer was formed by IBAD with a condition of Ar-30 kV and 2.1 μA/cm2, the adhesion strength increased to 10.7 MPa. Furthermore, that increased up to 44 MPa in the case of 21.0 μA/cm2. Therefore, it was realized that IBAD improved the adhesion of DLC films and the effects were made clear quantitatively.

Effects of ion beam bombardment of carbon thin films deposited onto tungsten carbide and tool steels

Abstract A study was made of the effects of argon ion bombardment of carbon thin films deposited onto WC and tool steels. Carbon thin film deposition was performed at various temperatures ranging from 200 °C to 350 °C, using C 6 H 6 gas. Argon ion beam bombardment of the films was carried out at an energy of 150 keV with a dose of 1×10 16 ions cm -2 . The hardness and adhesion of the films were measured by means of Knoop hardness and scratch tests respectively. The structure of the carbon films was estimated by laser Raman spectroscopy, and the relations were investigated between the mechanical properties and the structure of the films. The hardness of carbon thin films increases as their deposition temperature decreases; this tendency corresponds to the increase in amorphous structure estimated by Raman spectra. Argon ion bombardment results in constant hardness and fraction of amorphous structure. Argon ion beam bombardment of films prior to additional carbon deposition may cause the adhesion of the subsequently deposited films to improve. It is concluded that argon ion beam bombardment is useful for improving the properties of carbon films deposited onto WC and tool steels.

Effect of ion implantation on ion-plated diamond-like carbon films☆

Abstract A Raman spectroscopic study has been carried out on the effects of ion implantation of argon or nitrogen on the structures of ion-plated diamond-like carbon (DLC) films. The carbon films were deposited on WC substrates at room temperature, 200, 250, 300 and 350 °C. Implantation of 150 keV Ar + or N + into the films was carried out with a dose of 1 × 10 16 ion cm −2 at room temperature. The structure of the carbon films was estimated by laser Raman spectroscopy. It was found that the Raman spectra for non-implanted and implanted DLC films consisted of four main peaks: two well-known peaks belonging to graphite and long-ranged-disordered graphite structures, and two other new peaks which can be considered as follows. One peak corresponds to an amorphous-like structure with C=C bonding, and the other peak corresponds to a kind of hydrogenated-like carbon with chains of alternate C=C and C-C bonds. The as-deposited DLC films had various structures, depending on the ion plating conditions. Ion implantation in DLC specimens changed their structures, making them the same. It is expected that an equilibrium of mutual transfer (amorphous graphite) was achieved during ion implantation.

The properties of BCN films formed by ion beam assisted deposition

A study has been made on the formation and the properties of boron carbonnitride (BCN) thin films. The BCN films were produced by ion beam assisted deposition, in which boron and carbon were deposited by electron beam heating and nitrogen was supplied by ion implantation simultaneously. The mechanical properties of BCN films were measured using a ultra micro hardness tester and a friction tester. The atomic ratio and the structure of BCN thin films were estimated by means of X-ray photoelectron spectroscopy, laser Raman spectroscopy and Fourier transform infrared spectroscopy. As preliminary results, it was found that the BCN films are higher in hardness and lower in friction coefficient than diamond-like carbon (DLC) films. The mechanical properties are discussed with the relation of surface composition and structure.

Diamond-like carbon thin film formation by ion-beam-assisted deposition

A study has been made of the formation of diamond-like carbon (DLC) thin films on tungsten carbide (WC), high speed steel (SKH) and silicon (Si) wafer by ion-beam-assisted deposition (IBAD). Carbon targets were sputtered by electron beams and the carbon particles were deposited on tool specimens of WC and SKH and on Si wafer. At the same time ion beams were irradiated on the specimens during carbon coating. The ion beams were produced by plasma ionization with a microwave method and were accelerated. The acceleration voltage was 20 or 35 kV and the total dose density was approximately 1 × 1017 ions cm-2. The carbon films on their specimens were analysed for structure by Raman spectroscopy, and adhesion and hardness tests were carried out. The IBAD carbon films were similar to diamond-like carbon films prepared by ion plating in terms of their structure and Knoop hardness. Adhesive DLC films were formed by IBAD. It was concluded that IBAD is useful for improving the adhesion of the carbon film to the substrate.

DLC films formed by hybrid pulse plasma coating (HPPC) system

Abstract A new coating system was developed which consists fundamentally of plasma CVD (chemical vapor deposition) and ion-mixing. The system employs pulsed-gas introduction, pulsed-plasma generation and plasma base ion implantation (PBII). In this paper the formation of DLC films by the HPPC system is reported. The plasma densities were measured using a Langmuir probe and a 10-GHz microwave interferometer. DLC films were formed on the surface of workpieces using hydrocarbon gases by the HPPC system, with monitoring plasma density during the coating process. Raman spectra of DLC films by the HPPC system are similar in shape to those by ion-plating, and the fractions of amorphous and graphite components in Raman spectrum gained by segregated four peaks decreased with the decrease of CH 4 /C 7 H 8 partial pressure ratios. The reason is considered that the larger the deposition rates of films become, the smaller the ion-mixing effects are. Furthermore, as the CH 4 /C 7 H 8 ratio becomes as low as 1, this phenomenon becomes more apparent. For the further study, the plasma density as well as the change in gas pressure in the chamber must be monitored for the formation of uniform DLC films.

Development of hybrid pulse plasma coating system

A new plasma coating system is developed, which incorporates plasma-based ion implantation (PBII) with pulse-gas introduction, as well as pulse-plasma generation. This system operates by combining plasma chemical vapor deposition (plasma CVD) with ion beam mixing. For to create a deposited layer with a uniform thickness, both gas introduction and plasma generation are performed in pulses. Gas is introduced into the chamber while the plasma is extinguished. Then a negative high voltage is supplied to the workpiece to perform atomic mixing by PBII. In this system a microwave-plasma source, which completely eliminates static magnetic field, is adopted. The plasma is ignited with the help of inductively coupled RF power of 13.56 MHz, and the density is then increased by absorption of 2.45 GHz of microwave power. In this paper, the principle of the new hybrid pulse-plasma coating system and some of the fundamental performances are described.

Films formed by hybrid pulse plasma coating (HPPC) system

A new coating system was developed which consists fundamentally of plasma CVD and ion mixing. The system employs plasma-source ion implantation (PSII) combined with pulsed-gas introduction and pulsed-plasma generation. The Hybrid Pulse Plasma coating (HPPC) system is constructed from three main components, that is, a pulsed-gas introducing apparatus, a pulsed RF-microwave generator for high-density plasma, and a negative high-voltage pulse power supply for PSII. The plasma densities were measured during the coating process using a Langmuir probe and/or a 10 GHz-microwave interferometer. Each process was monitored as a function of the plasma density as well as the change of the gas pressure. The mechanical properties of formed films were measured and the methods were discussed how to uniformly form films on complicated surfaces of three-dimensional workpieces.

Evaluation of raw hardness of DLC thin films prepared by IBAD

Abstract In this study, diamond-like carbon (DLC) films were prepared by ion beam assisted deposition (IBAD), and micro-indentation tests were performed to evaluate the raw hardness that was independent of both the film thickness and the substrate hardness. As a result, the hardness constant proportional to the square root of the product of the Vickers hardness and elastic modulus was defined by analyzing the loading curves. Then, the raw hardness of the DLC films on tungsten carbide (WC) or high-speed steel (HSS) was evaluated by using the hardness constant. The effects of ion species in IBAD and the substrates with the different hardness were discussed. It was concluded that the evaluation by using the hardness constant proposed in the present study was useful for determination of the raw hardness of DLC films prepared by IBAD.