Abstract
Silicon nitride compound deposited by plasma enhanced chemical vapor deposition (PECVD) on plasma nitrided stainless steel 316L using tetraethylorthosilicate (TEOS):H2:N2 mixtures. Plasma nitriding is extensively used to improve the hardness and wear performance of steels. It is also known that silicon nitride compounds can have interesting properties, such as low friction coefficient, high hardness and wear resistance. Therefore the deposition processes were carried out at optimized gas compositions and temperatures in order to obtain a combination of the best mechanical and enhanced tribological properties. The composition and structure of the surface layers were characterized using XRD, Glancing angle X-ray diffraction (GAXRD), optical and EDX built in electron microscopy, Microhardness and pin-on-disc wear tests. The compound of α-Si3N4 was found on the top surfaces of PECVD and plasma nitrided austenitic stainless steel 316 L. The nitride compounds were composed of Fe2-3N, Fe4N in addition to chromium nitride. PECVD treatments substantially improved the hardness and wear resistance of plasma nitrided SS 316 L and reduced the friction coefficient and wear rate of the samples. The investigation showed that the combination of PECVD of organosilicon compounds and plasma nitriding results in superior hi gh hardness, low friction and high wear resistance of treated surfaces if compared to those of conventional plasma nitrided surfaces.
Highlights
In recent years, the treatment of surfaces with oxides and nitrides has increasingly gained importance in wear resistant applications
Plasma nitriding of all samples was performed at 500 °C and resulted in the formation Fe2-3N and Fe4N and chromium nitride (CrN) compounds on the surface
At 500 °C, the nitrides like CrN, Fe2–3N and Fe4N form due to partial decomposition of the metastable supersaturated austenite phase [19]
Summary
The treatment of surfaces with oxides and nitrides has increasingly gained importance in wear resistant applications. Anti-abrasion layers are necessary to increase the hardness and improve the resistance of surface against strokes, impacts of small particles and large pieces as well as friction. Industries use stainless steels for the good corrosion resistant and toughness of these materials where contact pressures are not considerable [1,2]. The high demand for these alloys requires the improvement of their surface hardness and wear resistance. Nitriding improves the surface hardness and wear resistance of various steel materials, such as tool steels and stainless steels. Thermo-chemical diffusion treatments such as nitriding and carburizing processes alter the surface of austenitic stainless steels as a main group of these materials [3,4,5,6]. The investigators carry out nitriding merely at low temperatures using liquid, gas or plasma environments; the industry is being more interested in plasma nitriding over traditional gas and bath nitriding [7,8,9]
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