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Abstract: Amorphous carbon nitride thin films were deposited on polymer substrates using radio frequency (rf) plasma in a mixture of nitrogen (N2) and acetylene (C2H2) gasses. The samples were prepared at different rf plasma power (350, 400, 450, 500, and 550W), at constant plasma exposure time of 10min, and constant N2/C2H2 ratio of 50%. The crystal structure and surface morphology of the prepared samples were examined using X-ray diffraction and atomic force microscopy analysis, respectively. The absence of the carbon nitride diffraction peaks confirms the amorphous nature of these films. The root mean square roughness of the films increased from 3.77 to 25.22nm as the power increased from 350 to 550W. The thickness and the deposition rate were found to increase with increasing plasma power. Over the whole studied wavelength range, from 200 to 2500nm, the transmittance decreased with increasing plasma power. A shift in the onset of absorption towards higher wavelengths with increasing plasma power, indicating a decrease in the optical band gap, has been observed. The refractive index values were found to decrease while the extinction coefficient increased with increasing plasma power. [Copyright &y& Elsevier]

Abstract: The present work reports on the effect of input plasma processing power in the range of 350–650W on the microstructure and mechanical properties of plasma nitrided Ti. The plasma processing time was 20min and a gas mixture of 15% C2H2 and 85% N2 was used. The characteristics of the carbonitrided layer have been investigated by microhardness measurements, surface roughness measurements, optical microscopy, and X-ray diffraction. The measured surface hardness values of the compound layer shows a maximum of 2050HV0.1 for the sample treated at a plasma power of 550W. The thickness of the carbonitrided layer continuously increases as the plasma power increases. Moreover, the highest carbonitriding rate of 3.52μm2/s was observed when the input plasma power was adjusted at 600W. This high carbonitriding rate of treated titanium samples is ascribed to the high concentration of active carbon and nitrogen species in the plasma atmosphere and the formed microcracks in the near surface of the sample during the plasma processing. [Copyright &y& Elsevier]

Abstract: Radio frequency (RF) plasma nitriding using different input plasma processing powers (250–600 W) improves the surface of titanium by forming hard phases of TiN, Ti2N, and Ti (N) into the surface. The characteristics of the compound layer have been investigated by optical microscopy, microhardness measurements, and X-ray diffraction. The effect of plasma power on the sample temperature, electron temperature, and plasma density was studied using Langmuir double probe. The measured surface hardness value of the compound layer is 2190 HV 0.1 for treated sample at plasma power 500 W. The compound thickness continuously increases as the plasma power increases. The highest nitriding rate of 5.88 μm2/s was recorded when the input plasma power was adjusted at 550 W. This high nitriding rate of treated titanium samples is ascribed to the high concentration of active nitrogen species in the plasma atmosphere and the formed microcracks near to the surface of the sample during the plasma processing. We have proposed that at low input plasma power (low temperature) the interstitial diffusion is the main mechanism. However, vacancy-controlled diffusion for high input plasma power (high temperature) is probably the one needed to surmount the energy barrier. [Copyright &y& Elsevier]

A systematic study was undertaken with surface of titanium nitrided by Rf inductively coupled plasma. The continuous plasma processing time was changed from only 3 to 40 min in steps of 5 min or less. The other plasma parameters were fixed. The effect of cyclic plasma processing time on titanium sample was investigated too. The single period of plasma processing was adjusted to be 25 min and the nitriding process was repeated twice, triplet, and quadruple. X-ray diffraction (XRD), optical micrograph (OM), and Vickers microhardness (HV) were employed as analytical techniques. The results clearly show that the surface hardness and nitriding rate increase incessantly as the continuous plasma processing time increases to reach the maximum values of 2150 HV0.1 at 40 min and 3.38 μm2/s at 30 min, respectively. This behavior may be attributed to formation of new hard phases α-Ti(N), δ-TiN, and #x03B5;-Ti2N in the treated layer. In this interval, the active nitrogen species penetrate faster through surface grain boundaries and through the formed surface microcraks of titanium sample. For relatively long nitriding time more than 30 min of continuous plasma processing, the rate of nitriding decreases. The formed nitrided phases might block the previously formed microcracks in the treated layer. Therefore, the penetration of nitrogen species rate through these microcracks decreases and the rate of nitriding process decreases consequently. Using cyclic nitriding method yielded an increase in the microhardness of titanium sample to be 2650 HV0.1 with relatively high rate of nitriding. These investigations show that the short Rf plasma processing time treatment and cyclic nitriding method play an important role for producing hard surface titanium with high rate of nitriding. [Copyright &y& Elsevier]

Adding C2H2 gas to nitrogen gas during r.f. plasma processing has significant influence on the properties of 304 austenitic stainless steel. The elemental depth profiles of the compound layer were investigated by glow discharge optical spectroscopy. Different treatment gas compositions of N2/C2H2 mixtures (0–100% in steps of 10 or 5% in some cases) have been investigated. The total gas pressure during the plasma processing was 8.4×10-2 mbar. The sample temperature was approximately 550 °C with an insignificant variation for different gas compositions. A high rate of diffusion of carbonitriding has been obtained without initial sputter removal of the surface oxide layer, which demonstrates that the surface oxide layer does not play a crucial role during r.f. plasma carburizing and carbonitriding of stainless steel. The nitrogen concentration and the compound layer thickness increase, when 10% of C2H2 is added. With further increase in the C2H2 ratio, they decrease again gradually. The carbon depth profiles for the same samples show lower concentration and opposite tendency with respect to the nitrogen content. X-ray diffraction was used to characterize the microstructure of the compound layers. Fe2N, Fe3N, CrN, nitrogen-expanded austenite (γn) and carbon-expanded austenite (γc) phases are detected. The relative proportions of the phases are critically dependent on the N2/C2H2 ratio. Depending on the N2/C2H2 ratio, the microhardness value increases by a factor between 2 and 6. The carbonitrid layer exhibits a corrosion resistance better than pure nitrided and carburized layers. [Copyright &y& Elsevier]