Nano-Thick Amorphous Oxide Layer Produced by Plasma on Type 316L Stainless Steel for Improved Corrosion Resistance Under Plastic Deformation

Abstract

Localized corrosion constitutes a major concern in medical devices made of stainless steel. The conventional approach to circumvent such a problem is to convert the surface polycrystalline microstructure of the native oxide layer to an amorphous oxide layer, a few micrometers thick. This process cannot, however, be used for devices such as stents that undergo plastic deformation during their implantation, especially those used in vascular surgery for the treatment of cardiac, neurological, and peripheral vessels. This work explores the feasibility of producing a nano-thick plastic-deformation resistant amorphous oxide layer by plasma-based surface modifications. By varying the plasma process parameters, oxide layers with different features were produced and their properties were investigated before and after clinically-relevant plastic deformation. These properties and the related corrosion mechanisms were mainly evaluated using the electrochemical methods of open-circuit potential, cyclic potentiodynamic polarization, and electrochemical impedance spectroscopy. Results showed that, under optimal conditions, the resistance to corrosion and to the permeation of ions in a phosphate buffered saline, even after deformation, was significantly enhanced.

On the adhesion of diamond‐like carbon coatings deposited by low‐pressure plasma on 316L stainless steel

“…43 1where EW is the equivalent weight of SS316L and d is its density: 27.9 SI and 7.8 g/cm 3 , respectively. 39,47 All the measurements were repeated three times.…”

“…37,38 The interface morphology and topography were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the corrosion behavior was evaluated by potentiodynamic tests. 39 The film adhesion on carburized SS316L substrates was assessed by a 25% plastic deformation process using a small-punch test device, 40 and analyzed by SEM after deformation. The long-term stability of DLC on SS316L, essential for coatings commercial use, was assessed on the deformed samples, after 1 year of environmental aging.…”

Surface modification and direct plasma amination of L605 CoCr alloys: on the optimization of the oxide layer for application in cardiovascular implants

“…This oxide layer must resist deformation related to the deployment of the device, and must be corrosion resistant to avoid the release of toxic ions in the blood stream, whilst being biocompatible. 6,10,11 Among the different strategies to modify the oxide layers and the nishing of metallic substrates, procedures can be divided into mechanical treatments, thermal treatments, ion implantation and chemical treatments. 12 All of these treatments can modulate properties such as chemical composition, surface roughness, corrosion and deformation resistance, wettability, blood compatibility and cytotoxicity.…”

“…12,13 In regards to ion implantation processes, such as plasma immersion ion implantation (PIII), these can produce changes both on the surface and in the internal structure, producing an amorphous oxide layer, due to the acceleration of ions into the metallic substrate. 11,[14][15][16] Finally, chemical treatments, for example electropolishing, allow for the removal of any surface contaminant and the passivation of the surface whilst obtaining a nano-smooth surface with a mirror like nish. 7,12,17 This study focuses on the surface preparation step of L605 alloys for their direct plasma amination.…”