ABSTRACT
Martensitic stainless steels can be used in different applications such as surgical instruments where a good wear and corrosion resistance are required. Surface modification treatments such as nitriding improve the mechanical properties of these steels, however; they affect the corrosion resistance. For this reason, the DLC (Diamond Like Carbon) coatings deposition can be convenient.
The wear and corrosion behaviour was studied in duplex samples (nitrided and PACVD coated) and they were compared with nitrided and only coated samples and with those without treatment, only heat treated (quench and tempering). The coatings were analyzed by Raman spectroscopy and EDS. Pin on disk tests were performed and the adhesion was evaluated using Scratch Test and Rockwell C Indentation. The nanohardness was measured with a Berkovich indenter. The corrosion tests for surgical instruments (according to the Standard ASTM F 1089 -02) and Spray Salt Fog tests were carried out.
In the DLC coatings, the ID/IG ratio was 0.8 and the hydrogen content was calculated and resulted to be about 20 %. The coating thickness was 2 µm and the hardness reached 24 GPa. The nitrided layer thickness was 10 µm. The duplex and coated samples presented low friction coefficient and the wear volume loss was undetectable. The coatings had good corrosion behaviour in the corrosion tests. Nevertheless, the nitrided sample presented a corroded region in the copper sulfate and boil tests. The duplex samples had better adhesion than the coated samples in scratch test and indentation Rockwell C.
Keywords
DLC coatings; AISI 420; wear; corrosion; surgical instruments
