This paper is concerned with plasma diagnosis on a N2-H2 gas mixture to determine the optimum parameters for the nitriding process. Plasma parameters such as pressure, RF-voltage, and DC-bias were varied for optimization. The active species such as N2+ and NH were identified in plasma diagnosis. In the N2-H2 gas mixture, hydrogen imposed a great influence on plasma generation. The small addition of a hydrogen molecule into the gas mixture resulted in the highest yield of N2+ ions and NH radicals; the optimum hydrogen content was 20% in the mixture. The austenitic stainless-steel type AISI304 was nitrided at 673 K and 623 K to experimentally demonstrate that hydrogen gas content optimization is necessary to improve the surface hardness and to describe low temperature nitriding under high nitrogen flux at the surface.
-Diamond-Like Carbon (DLC) and Chemical Vapor Deposition (CVD)-diamond films have been widely utilized not only as a hard protective coating for molds and dies but also as a functional substrate for bio-MEMS/ NEMS. Micro-texturing into these hard coated molds and dies provides a productive tool to duplicate the original mother micro-patterns onto various work materials and to construct any tailored micro-textures for sensors and actuators. In the present paper, the high density oxygen plasma etching method is utilized to make micro-line and microgroove patterns onto the DLC and diamond coatings. Our developing oxygen plasma etching system is introduced together with characterization on the plasma state during etching. In this quantitative plasma diagnosis, both the population of activated species and the electron and ion densities are identified through the emissive light spectroscopy and the Langmuir probe method. In addition, the on-line monitoring of the plasmas helps to describe the etching process. DLC coated WC (Co) specimen is first employed to describe the etching mechanism by the present method. Chemical Vapor Deposition (CVD) diamond coated WC (Co) is also employed to demonstrate the reliable capacity of the present high density oxygen plasma etching. This oxygen plasma etching performance is discussed by comparison of the etching rates.
Huge amount of CVD-diamond coated milling tools were used for machining of CFRP and CFRTP sheets and blocks in the airplane and automotive industries. Because of chipping and tooth-tip damage in the diamond coatings during those dry machining processes, the tools must be exchanged with new ones to preserve the geometric accuracy in practice. WC (Co) substrate in these used tools had to be recycled to lower the production cost; reliable ashing process was necessary to remove only the used diamond coatings without significant damages even to the tooth tip of substrate. Furthermore, fast-rate ashing became a key to shorten the leading time for exchange of milling and drilling tools. High density oxygen plasma ashing method with use of the hollow cathode device was proposed to remove the used diamond coating with the film thickness of 10 µm. Both the emissive-light optical spectroscopy and the Langmuir probe method were employed to make quantitative diagnosis on the generated oxygen plasmas. The average ion density increased up to more than 1x10 17 m -3 , higher than the conventional plasma states by one order. Activated oxygen atom had overwhelming population among the generated species in this high plasmas density. This high density oxygen flux was responsible for complete and fast-rate removal of CVD diamond coating; e.g. the average ashing rate turned to be more than 10 µm/hour. The short-shank, end-milling tools were employed to describe this ashing behavior with time. Corresponding to the variation of CO-peak intensity in the measured spectra by on-line spectroscopy, the diamond film thickness reduced monotonically with time up to 3.6 ks. The removal rate gradually decreased with time in the final stage. Fine tuning of oxygen plasma processing conditions was capable to reduce the damage depth of tool teeth tips down to 1 µm, significantly less than the standard tolerance of 5 µm.
High density oxygen plasma ashing of CVD-diamond coatingwith minimum damage to WC (Co) tool substrates
Plasma diagnosis has done by using Langmuir probe and software modeling. COMSOL and JMAG software were employed to characterize the electron density and identifying the set up effect in the plasma system. First, the COMSOL software was employed to simulate the behavior of electron density. The pressure and DC-bias voltage were varied during the simulation process. The DC bias voltage was varied in the range-200 V to-600V. The pressure was also varied in the range 30 to 80 Pa. The high electron density was generated in the high DC-bias voltage and high pressure by using simulation process. Second, the Langmuir probe was also employed to measure the behavior of electron density inside the actual plasma chamber. The DC-bias voltage and pressure were also varied in the range-350V to-650V and 60 Pa to 120 Pa, respectively. The experiment and modeling result were shown the same trend for the behavior of electron density. Third, the JMAG software was also utilized to characterize and modifying the set up in the plasma system. The electrode and DC bias was varied in the range 100 to 500 V and-100 to-500 V, respectively. The electric field distribution was concentrated in the electrode and DC-bias plate from the original set up. However, the electric field distribution was shifted to the center area after modification process. The modifications of experiment set up have provided the new way to confine the electric field. The high concentrated of electric field was effective to generate high plasma density.
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