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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]

Inductively coupled radio frequency plasma surface treatment was applied to commercially pure titanium sheets. The goal was to increase the efficiency of the carbonitriding process, i.e., to decrease the plasma treatment time to a few tens of minutes instead of several hours. The effects of different plasma-processing times on the microstructure and mechanical properties of plasma-carbonitrided Ti were examined. The characteristics of the carbonitrided layer were investigated by microhardness testing, surface roughness measurements, optical microscopy and X-ray diffraction. The surface microhardness and the thickness of the compound layer of carbonitrided Ti increase with the plasma-processing time. Surface energy, yield strength and Young’s modulus for carbonitrided titanium were calculated from the Vickers microhardness data. An attempt was made to interpret the high carbonitriding rate and the high microhardness values of carbonitrided titanium with respect to previously published results. [ABSTRACT FROM AUTHOR]

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]

Abstract: Plasma immersion ion implantation (PIII) has been used to modify the surface properties of 304 austenitic stainless steel (AISI). The influence of working gas pressure, 0.2–1.0 Pa, and substrate temperature, 300–500 °C, on the microstructure, treating rate, nitrogen/carbon concentration depth profile, and surface microhardness was investigated. A gas composition of 25% C2H2, 75% N2, r.f. plasma power input of 350 W, and a negatively biased potential of 30 kV were fixed during the experiment. The experimental results show that the substrate temperature and the diffusion process of nitrogen and carbon depend on the gas pressure inside the plasma chamber. The thickness of the modified layer has been found to be more than 30 μm for samples were treated in the plasma for 60 min. The results show also that the values of diffusion coefficient and surface microhardness of the treated samples are high to be 3.4×10−1 μm2/s and 1880 kg/mm2, respectively. [Copyright &y& Elsevier]