ICMCTF2015 Session GP: Symposium G Poster Session

Silica-based films are widely used by polymeric materials for industrial fields due to their properties such as optical transparency, gas barrier property, hardness and low-k. A linear type atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) method using DBD system has been attracted much attention as a method of high-speed synthesis to large area. However, deposition on a tridimensional figuration or thick substrate using a conventional linear type AP-PECVD method is impossible because substrates set in the discharge region whose gap typically is a few millimeters. A remote-type PECVD method which the plasma stream exits the discharge generation region between electrodes enables the deposition to complex configuration substrates.

In the present paper, the plasma nitriding assisted texturing is proposed as an alternative method to form the millions of micro-dimples on the stainless steel mold-die surface in the order of 10⁴ s. First, the original micro-texture pattern is printed onto the mold-die surface and followed by the low temperature plasma-nitriding. In the latter, significant amount of nitrogen atoms is infiltrated into the unmasked regions of surface; e.g. 5 mass% down to the depth of 16 – 20 mμm after plasma-nitriding for 7.2 ks at 693 K. Since the unmasked regions have hardness more than 1400 Hv, the printed micro-patterns are selectively removed down to 10-15 mμm in depth via the mechanical blasting for 100 s. This surface-treated mold-die is utilized as a mold for injection molding of plastic parts; i.e. the micro-dimple pattern formed on the mold-die by the present method is transferred onto the surface of plastic parts as a micro-bump pattern.

In the present paper, the hollow-cathode oxygen plasma etching system is developed to make fast-rate micro-texturing onto the CVD-diamond coatings with the depth of 20 μm on the WC (Co) and silicon substrates. Two types of imprinting procedures are employed to construct the original two-dimensional micro-patterns onto the surface of diamond films: ink-jet printing and mask-less patterning. The former method is used to imprint the micro-dot and micro-line patterns with the characteristic size down to 10 μm onto the diamond film. After the present etching for 7.2 ks, these 2D micro-patterns are transformed into micro-disc and micro-grid textures with the height of 20 μm. Through precise analysis by the Raman spectroscopy, no diamonds area left on the etched bottom surfaces of these micro-textures. The surface profiling measurement proves that the formed edges in these micro-discs and micro-grids have higher steep angles than 87^o. The latter method is also used to make finer micro-textures with the spatial resolution down to 1 μm. Micro-pillar patterns with higher aspect ratio than 10.0 are formed by this high-density plasma etching when starting from the 2D micro-dot patterns with the diameter of 1 μm.

It is widely known that the performance of a drilling tool increases with the application of coatings. Nowadays, the most widely used coatings for machining aluminum alloys are TiCN and TiN, due to their mechanical properties such as high hardness with low friction. This work presents a study on the performance of cemented carbide coated with diamond-like carbon (DLC) in the drilling of aluminum alloy, since the DLC is a promising material as a coating and has the same mechanical characteristics of the coatings used regularly. Samples of DLC coatings were deposited using PECVD. Initially, the adhesion between film and substrate did not occur. In order to avoid this, it was added intermediate silicon layer. After an extensive investigation of the deposition parameters, drilling coated tools were obtained. The characterization of the tool substrate through the X-ray diffraction showed the standard pattern of the WC-Co. For the coating, the typical spectrum of DLC was checked by Raman spectroscopy. An amount of two hundred pieces of molten on aluminum alloy (SA-323) were chosen for the respective analyzes of roundness, radial deviation, deviation of diameter and roughness. All these geometries were measured as a function of the number of holes produced by each tool, under coated and uncoated condition. Visual inspections by SEM and EDX analysis of worn tool were performed before and after each sequence. Finally, it was found that the DLC coating improves the tool performance, improving the geometry quality. However, the effect of peeling on the coating gradually increased.

The chemical vapor deposition (CVD) method is one of the reliable methods for growing carbon nanotubes (CNT). This method generally enables growing the vertically aligned CNTs on the substrate, which is a suitable feature as the interconnections in an integrated circuits (IC) and electrodes of electrical double layer capacitors (EDLC) etc. It has been reported that the water addition into the source gas increased the growth speed of CNT. In this study, the effects of the water addition on the CNT growth was investigated.

Vertically aligned CNTs were formed by using thermal CVD method on Si substrate. Fe particles on Si substrate were used as the catalyst of CNT growth. Acetylene and argon gases were used as source gas. The concentration of acetylene gas and the total gas flow rate were kept at 2 % and 1000 sccm, respectively. Water addition into the source gas was carried out by flowing argon gas into the water. The flow rate of argon gas flowing into the water was varied from 0 sccm to 10 sccm in order to control the concentration of water vapor in the source gas. Growth temperature and time was 750 oC and 15 minutes, respectively.

The vertically aligned CNTs with the length of 140 micro meters were formed on the Si substrate without the addition of the water vapor into the source gas. The growth speed of the CNTs was increased with the addition of the water vapor. The CNTs with the length of 520 micro meters were formed at the growth time of 15 minutes, when the argon gas was flowed at 6 sccm into the water for the addition of the water vapor into the source gas. When the argon gas was flowed into the water above 7 sccm, the growth speed was decreased. At the flow rate of 8 sccm, the length of the CNT was lower than that of the CNT deposited without the addition of water.

Our current study on the successful plasma treated γ-APS coating of polypropylene (PP) has improved the gas barrier property of PP by a factor of 15. The positron annihilation lifetime spectroscopy (PALS) revealed the decrease in the size of the free volume at the surface of the plasma treated γ-APS coating. To understand the mechanism of the improvement in the gas barrier properties of γ-APS/PP, this work focused on the investigation of the relation between the gas barrier enhancement and the structural change of γ-APS/PP caused by the alteration of the plasma power.

The plasma treatment time was fixed to 5 seconds, while the plasma power was shifted from 50 to 200 W. It was found that the oxygen transmission rate (OTR) was considerably reduced from 809.3 cc/m²/day/atm to 262.9 at the power of 200 W. The atomic fractions of the components of Si, O, C, and N at the surface of the γ-APS/PP were analyzed by X-ray photoelectron spectroscopy (XPS), revealing that C-atom fraction was decreased from 37.5% to 13.9% and Si-atom fraction increased from 17.8% to 23.5% after the plasma treatment. It was consequently surmised that the γ-APS surface was converted into SiO_x by the plasma treatment, while the C-atom fraction was decreased by the etching effect of the plasma. The C-atom was found to be at the fragment state of C₄H₁₀N or C₈H₁₄NO after the treatment, which was revealed by the time of flight secondary ion mass spectroscopy (TOF-SIMS). Such fragments were considered to make the free-volume size larger, and thus the decreasing amount of the C-atom fraction was important for the improvement of the gas barrier properties. In fact, the C/Si ratio calculated from the fractions was found to be strongly related to the OTR results, which was also confirmed in other plasma treatments. It was concluded that the effective plasma processing of the γ-APS crosslinkings into SiO_x and the significant reduction of the amount of C fragments lessened the size of the free volume at the surface of the plasma-treated γ-APS coating, leading to the improvement in the gas barrier properties of PP.

Plasma sprayed ceramic coatings are used for various industrial applications like thermal insulation, electrical insulation or corrosion protection. The interfacial strength of a ceramic coating is a key issue to achieve reliable coated components. The laser shock technique allows to debond a ceramic coating. The LASAT method (LAser Shock Adhesion Test) enables to measure the adhesion strength of a ceramic coating if the crack is located at the interface. In case of conventional ceramic coatings, it leads to a cracked disk area of a few mm² at the ceramic/metal interface and subsequent coating buckling. In this work, the LASAT method is applied to investigate the influence of various morphologies of the substrate on the resulting damage induced by laser shock at the interface or within the ceramic coating. Several processes were implemented to obtain different surface morphologies on a cobalt base alloy substrate. Random or deterministic surface morphologies were carried out involving either removal methods (grit blasting and electric discharged machining) or additive methods (plasma spraying and laser beam melting). A ceramic coating was then deposited on the different structured substrates by air plasma spraying. The size, location and profile of the laser-induced cracks were assessed with both destructive (scanning electron microscopy) and non-destructive (infrared thermography, 3D profilometry) methods. These crack features and the height of the buckling are discussed paying attention to 2D and 3D analyses of the morphology at the interface. The influence of the shock wave propagation through such structured interfaces is also discussed. From the assessment of the debonding behaviour under laser shock, a comparison of the interfacial strength level for the various interfaces is proposed.