| AVS 61st International Symposium & Exhibition | |
| Tribology Focus Topic | Thursday Sessions |
| Session TR-ThP |
| Session: | Tribology Poster Session |
| Presenter: | Petros Abraha, Meijo University, Japan |
| Authors: | P. Abraha, Meijo University, Japan S. Mikashima, Meijo University, Japan |
| Correspondent: | Click to Email |
Stainless steels have very good corrosion resistance but the lower surface hardness poses marked limitation on the range of tribological applications that can be envisaged. Here plasma nitriding treatment was performed to modify the hardness without altering the corrosion resistance of austenitic 316L stainless steels.
In nitriding the 316L stainless steel, the passive CrO2 layer that protects the surface from corrosion is removed first as it hinders the diffusion of nitrogen ions and atoms into the bulk of the stainless steel material. The removal of the passive layer was done by argon sputtering and the subsequent plasma nitriding was performed in electron beam excited plasma apparatus under nitrogen atmosphere for three hours. The apparatus was driven at an acceleration voltage of 100 volts and a beam current of 3 amperes. The sample temperature was held constant at 450 degree centigrade. Treated and untreated samples were characterized by means of morphological analysis, Vickers hardness measurements, and corrosion tests in NaCl solutions.
The results of our experiments show that nitriding treatments performed in primarily ion and neutral environs have increased hardness, slightly lower chrome concentration, and hence slightly higher quantity of rust. The measured hardness, chrome concentration, and quantity of rust for the non-treated samples were 230 Hv, 17 mass%, and 4 g/m2, respectively. Ion nitriding in contrast largely increased the surface hardness of the stainless steel samples (more than 6 times), but decreased the corrosion resistance properties due to the CrN precipitation (15.8 mass %). Nevertheless nitriding treatments performed under neutral nitriding increased the surface hardness of the stainless steel samples (more than 3 times), avoid a large CrN precipitation (16.8 mass %) and rust quantity of 7.8 g/m2 that is much lower than the 350 g/m2 for ion nitriding. The above results indicate that stainless steels can be used as sliding or meshing mechanical parts in environments such as vacuum chambers and underwater machinery.