**3. Results**

340 Corrosion Resistance

of 8.4x10-2 mbar. The sample was heated mainly by the rf field. The sample temperature was measured during the rf plasma process by a Chromel-Alumel thermocouple, attached to the sample holder. As shown in Fig. 1, the substrate temperature was influenced by the effect of gas compositions. It was found that the temperature gradually increases from 475 °C for pure nitriding up to 550 °C for carbonitriding (50% C2H2, 50% N2) and raises up to 600 °C for pure carburizing. Grazing incidence X-ray diffraction (GIXRD) with Cu Kα radiation was used to determine the phases, present in the treated layers. For the chosen incidence angle of 2° the (1/e)-penetration depth of the X-rays was approximately 700 nm. The recorded diffraction pattern shows therefore mainly the structure of the phases formed in this near-surface region. In this paper we concentrate on the study of corrosion resistance, surface morphology before and after corrosion, and tribological properties of the treated samples. The surface roughness was measured by use of the rough machine (Dektak 8000, Veeco Instrument GmbH). Wear and friction measurement were performed at room temperature in laboratory air with low humidity of 16 to 24 % using an oscillating ball-on-disk type tribometer wear tester without lubrication. The 3-mm ball of cobalt tungsten carbide was moved at mean sliding speed of 15 mm/sec with different normal loads of 3, 5 and 8 N. The corrosion properties were evaluated using the electrochemical testing technique. The corrosion tests were performed in a 1 wt. % NaCl solution by application of the potentiodynamic polarization method. A three-electrode electrochemical cell has been used, counter and reference electrode were related to Pt and saturated calomel electrode, respectively.

Fig. 1. Temperature variation as a function of the gas composition.
