Study of Surface Structure, Morphology and Hardness of Several Different Diamond-Like Carbon Films
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wheels resting perpendicular to the sample surface. The sample is rotated, causing the abrasive wheels to rotate in opposite directions, thus abrading the sample surface. A vacuum nozzle is positioned just above the sample surface to remove debris caused by abrasion. The weight chosen in this study was 500g. After samples were abraded 100 revolutions, the intensity of damage was quantified by measuring the percentage of haze with an integrating sphere haze meter according to the ASTM D 1003-61 method[ 10]. Haze measurements were obtained for the PC before and after DLC coating, and after the Taber abrasion testing using a Gardner Haze meter UX10, and a PG-5500 Digital Photo Metric Unit for the read out. b) Nanoindentation The hardness of the DLC coating on PC substrate was measured using a Nano Instruments Inc. Nano IndenterTm II. The hardness of all the DLC films and the PC substrate with and without siloxane hardcoat were recorded at three different depths: 20, 40 and 80 nanometers(nm). Each sample was indented ten times at ten randomly selected locations.
c) Ballistic Testing Ballistic testing was carried out using a standard .22 caliber fragment simulator projectile weighing 1.10 grams. The projectiles were fired from a 1.23 m long gas gun which is connected to a high speed solenoid valve leading to a helium gas cylinder[l 1]. Before firing, a desired pressure was selected, then the gun was fired by manual closure of an electrical circuit which opened the solenoid valve. The projectile velocities were determined by a pair of printed silver grid-paper screens located in front of the specimen and connected to an electronic chronograph for time-off-flight measurements. Because of the limited number of specimens, impact response was not rated in terms of a characteristic projectile impact velocity V50. This quantity is defined as the projectile impact velocity at which there is 50% probability of complete penetration of the target Ballistic tests were performed in order to determine the effects of the coating and coating process on the impact behavior of the PC. Chemical Exposure PC coupons coated with various DLC thin films were exposed to various chemicals, including chloroethylethylsulfide (CEES) which was injected from a three microliter syringe at room temperature. Each test specimen was covered with an inverted watch glass to prevent evaporation. Coupons, after exposure to chemicals for a certain period of time, were examined for deterioration with either an optical microscope or a scanning electron microscope. Environmental Conditioning The DLC coated PC samples were conditioned in an environmental chamber set at 71 0 C and 90% humidity for accelerated weathering. RESULTS AND DISCUSSIONS Material Characterization Visually and from SEM, the DLC films appeared to be smooth and uniform. Atomic Force Microscopy (AFM) revealed some small bumps and particles on the surface. X-ray Photoelectron Spectroscopy could not differentiate the sp2 and sp 3 carbon bonding. Scanning Auger Spectroscopy was used to determine t
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