Yenilmez, A.; Karakan, M.; Çelik, I.

Austenitic stainless steels are widely used in several industries such as chemistry, food, health and space due to their perfect corrosion resistance. However, in addition to corrosion resistance, the mechanic and tribological features such as wear resistance and friction are required to be good in the production and engineering of this type of machines, equipment and mechanic parts. In this study, ferritic (FNC) and austenitic (ANC) nitrocarburizing were applied on AISI 316 stainless steel specimens with perfect corrosion resistance in the plasma environment at the definite time (4 h) and constant gas mixture atmosphere. In order to recover corrosion resistance which was deteriorated after nitrocarburizing again, plasma postoxidation process (45 min) was applied. After the duplex treatment, the specimens’ structural analyses with XRD and SEM methods, corrosion analysis with polarization method and surface hardness with microhardness method were examined. At the end of the studies, AISI 316 surface hardness of stainless steel increased with nitrocarburizing process, but the corrosion resistance was deteriorated with FNC (570 °C) and ANC (670 °C) nitrocarburizing. With the following of the postoxidation treatment, it was detected that the corrosion resistance became better and it approached its value before the process.

Çelik, I.; Karakan, M.

Commercial pure titanium (CP-Ti) is used in many engineering fields because of its superior properties such as excellent corrosion resistance, high strength/weight ratio, and biocompatibility. However, it is not available at the desired rate, since the CP-Ti has poor wear resistance. For this reason, many surface treatments have been applied to improve the poor tribological properties of the CP-Ti. In this study, duplex surface treatments, which are the combination of treatments of electroless Ni-B coating and plasma nitriding, were applied on the surfaces of the CP-Ti. Structural properties of the different surfaces of the treated materials were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Microhardness measurements were made for the determination of mechanical properties and the pin-on-disk wear tests were made to determine the tribological properties. It was observed that poor wear resistance of the CP-Ti was improved with duplex surface treatments. The results showed that surface hardness, friction coefficient, and surface roughness of coated samples were better than of uncoated CP-Ti.