Yoshinori Funada

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.

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.

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.

EFFECTS OF H-IMPLANTATION ENERGY ON THE OPTICAL STABILITY OF IMPLANTED URUSHI FILMS UNDER PHOTO-IRRADIATION

A study has been made on the improvement of the optical stability of urushi films under optical irradiation using ion implantation. Ion implantation of hydrogen ions in urushi films was performed with a dose of 1015 ions/cm2 at ion energies ranging from 0.2 to 150 keV at room temperature. The photo-irradiation onto the urushi films was carried out at irradiation energies ranging from 40 to 400 MJ/m2. H-implantation onto urushi films is useful for improving the optical stability under photo-irradiation when the implantation energy is larger than 60 keV.

Lap welding with direct diode laser of thin foil on thick substrate

Lap welding of thin foils on thick substrate is required for manufacturing of electronic devises such as a pressure sensor. The decrease of thickness of foils makes lap welding of them on thick substrates more difficult because of the generation of the thermal distortion around the heating area and so on. Heat conduction welding with an elliptical beam of a direct diode laser is effective in butt-welding of thin foils because of slight thermal distortion caused by the low power density. Lap welding of thin foils on thick substrates was examined with a direct diode laser system. Lap welding of thin stainless foils of 20µm in thickness on thick substrate of 2mm in thickness was made possible at a high welding speed of 0.5m/sec without wrinkles, by a sufficient contact of the thin foils with the substrates and pre-heating. It was recognized that heat conduction welding with a direct diode laser was applicable to lap welding of thin foils on thick substrates.Lap welding of thin foils on thick substrate is required for manufacturing of electronic devises such as a pressure sensor. The decrease of thickness of foils makes lap welding of them on thick substrates more difficult because of the generation of the thermal distortion around the heating area and so on. Heat conduction welding with an elliptical beam of a direct diode laser is effective in butt-welding of thin foils because of slight thermal distortion caused by the low power density. Lap welding of thin foils on thick substrates was examined with a direct diode laser system. Lap welding of thin stainless foils of 20µm in thickness on thick substrate of 2mm in thickness was made possible at a high welding speed of 0.5m/sec without wrinkles, by a sufficient contact of the thin foils with the substrates and pre-heating. It was recognized that heat conduction welding with a direct diode laser was applicable to lap welding of thin foils on thick substrates.

Micro-Welding of Thin Foil with Direct Diode Laser

Recently, industrial products parts and components are being made smaller to reduce energy consumption and save space, creating a growing need for micro-welding of thin foil less than 100 mm thick. For this purpose, laser processing is expected to be the method of choice because it allows more precise heat control compared wih arc and plasma processing. In this report, the practicability of welding thin stainless steel foil with a direct diode laser system was investigated. The elliptically shaped laser beam of the direct diode laser enabled successful butt-welding of thin stainless steel foil 100 μm and less in thickness. Foil as thin as 50 μm could be successfully welded with a narrow bead width of 150 μm at a high speed of 18.0m/min. No spatter or plasma plume was observed when welding without an assist gas. The tensile strength of the weld bead was nearly the same as that of the base material.

Heat conduction welding of thin foils with elliptical beam of direct diode laser

A finely focused elliptical beam of a direct diode laser was applied to lap welding of thin foils on thick substrates. This beam shape enabled welding with a narrow bead at a high speed and low power. The welding phenomena were very calm because of its low power density. An elliptical beam of 230 µm x 1800 µm successfully welded thin stainless steel foil of 5µm in thickness on 1mm thick stainless steel substrate. These characteristics are caused by the heat conduction type welding with the low power density elliptical beam. In this report, characteristics of heat conduction welding of thin foils with a finely focused elliptical beam of direct diode laser will be discussed with welding parameters such as power, power density and welding speed.A finely focused elliptical beam of a direct diode laser was applied to lap welding of thin foils on thick substrates. This beam shape enabled welding with a narrow bead at a high speed and low power. The welding phenomena were very calm because of its low power density. An elliptical beam of 230 µm x 1800 µm successfully welded thin stainless steel foil of 5µm in thickness on 1mm thick stainless steel substrate. These characteristics are caused by the heat conduction type welding with the low power density elliptical beam. In this report, characteristics of heat conduction welding of thin foils with a finely focused elliptical beam of direct diode laser will be discussed with welding parameters such as power, power density and welding speed.

Synchrotron x-ray induced real time observations of CoCr alloy layer formation by micro laser cladding

The direct injection type laser cladding system using combined multi lasers, which supplies a clad powder from a center nozzle, was developed for realize of low dilution area and micro cladding. A fiber coupled diode laser was employed. The six-diode lasers were guided to focusing head with every optical fiber, which core diameter is 100 μm. Beam profile at focal point of the combined six lasers was set a spot diameter of 300 μm by CCD camera. Here, A cobalt-chromium alloy (CoCr-alloy) called by Stellite, which has excellent properties such as wear resistance, corrosion resistance and resistance to environment, was used as a cladding material. The focusing head has a function to supply a CoCr-alloy powder at a focal point from a center nozzle. When the laser irradiation and powder supply are simultaneously performed toward to a stainless steel 304 substrate, the CoCr-alloy powder was melted and solidified on the substrate to form a cladding layer. The melting and solidification process for CoCr-alloy was observed in real time using synchrotron radiation imaging technique at BL22XU in SPring-8. From results, it was clarified that the CoCralloy melt-solidification phenomenon greatly differs for laser output power. At the output power of 60W, it was found that a minimum amount of molten pool was formed and then solidified to form the cladding layer.

Development of laser metal deposition technology with IR and blue diode lasers (Conference Presentation)

Laser cladding, which is one of laser metal deposition (LMD) technologies, is an effective metal surface coating technique capable of increasing component lifetimes, in which an additive material such as a powder or a wire is melted by a laser beam and deposited on the substrate surface. We developed a multi-beam processing head with six high intensity infrared (IR) diode lasers, which was based on multi laser combining method, in order to realize a high quality cladding layer having a dense, fine and purity. An IR diode laser light with the power of 50 W was output from an optical fiber. Total laser power on the base plate was 300 W since six laser beams were overlapped. A nozzle to supply the powder was in the center of the processing head. The processing head was installed in a machine tool (simultaneous 5-axis machining). Hardness and abrasion resistances of blade edge and shaft made from stainless steel were improved by cladding of cobalt-base alloy powder, which was one of the applications with the machine. We also designed a multi-beam processing head with high intensity blue diode lasers for cladding of copper powder. We have developed a high intensity blue diode laser with the power of 100 W. The blue laser light was output from an optical fiber whose core diameter and NA were 100 m and 0.22, respectively. The three blue diode lasers would be installed to the processing head to obtain the power of 300 W on the base plate

In-situ x-ray observation of molten pool dynamics while laser cladding with blue direct diode laser

A blue direct diode laser cladding system, which uses multi laser combining method, was developed in order to realize a high quality cladding layer having a dense, fine and purity. In order to clarify the mechanism of copper layer formation, the layer formation process when forming a copper layer using a blue direct diode laser was observed using in situ X ray observation. The six-blue diode lasers were guided to focusing head with every optical fiber, which core diameter is 100 μm. Beam profile at focal point of the combined six lasers was set a spot diameter of 400 μm. The focusing head has a function to supply a pure copper powder at a focal point from a center nozzle. As the results, it was found that the stainless steel 304 substrate was melted and generate some bubble in molten pool at laser fluence of 1221 kJ/cm2, and output power of 92W. At laser fluence of 407 kJ/cm2, the bubble was not appeared because only a slight molten pool was formed on the surface of the substrate. It was found that amount of bubble and penetration depth was depended on the laser fluence with blue direct diode laser. By controlling the amount of input energy, the copper coating was produced minutely with no weld penetration.