Microstructural Characterization of 316L-Type Stainless Steel Exposed to SiFX Species in Argon Atmosphere

Abstract

ABSTRACTNowadays, Si3N4 coatings are used to increase the hardness of 316L-type stainless steel for a wide variety of applications. These coatings are normally prepared by chemical vapor deposition (CVD) or variant techniques such as the hybrid solid-gas precursor system chemical vapor deposition (HYSYCVD), where Na2SiF6 is used as a solid precursor. Within the reaction chamber the Si-F gas species interact with nitrogen precursors to form Si3N4; however, during silicon nitride formation there is always certain amount of residual Si-F gas species which may affect the integrity of the steel surface. Therefore, in this work the effect of the Si-F species on the surface of 316L type stainless steel under argon atmosphere has been investigated. Stainless steel samples were prepared under two surface conditions (abraded and mirror polished), and were exposed to Si-F species considering various parameters such as: argon gas flow rate equal to 10 cm3/min, different temperatures (300, 500, 700, 900°C), and three exposure times (30, 60, 90 minutes). After exposure, the substrates were characterized by X-ray diffraction (XRD) and by scanning electron microscopy (SEM). The results show that the FeF2 phase is formed at low temperatures while the formation of different oxides is directly related to the processing temperature. What is more, these oxides are also strongly influenced by processing time; however temperature is the parameter that most significantly influences the oxides formation.