Electrolytic-plasma polishing of cobalt-chromium alloys for medical products

Abstract

In the manufacture of implants that are subject to increased cyclic loads, cobalt-chromium alloys with high hardness- and wear resistance have recently been widely used. Roughness of working surfaces is one of the most important characteristics of such products. The traditional processes of finishing the surface of cobalt-chromium alloy implants are based on mechanical and electrochemical methods. The disadvantages of mechanical methods are low productivity, susceptibility to the introduction of foreign particles, difficulties in processing of complex geometric shapes. For electrochemical technologies the treated materials are considered intractable, harmful electrolytes, consisting of solutions of acids, are used in the process of polishing. As an alternative to existing methods, it was proposed to use an environmentally safe method of electrolytic-plasma polishing, the main advantage of which is the use of aqueous solutions of salts with a concentration of 3–5 % as electrolytes. According to the results of the technological process, it has been established that at most electrolyte-plasma polishing modes of cobalt-chromium alloys for medical purposes, a relief in the form of a grid of protrusions occurs on the surface, the origin of which can be explained by the heterogeneity of the material structure that occurs at the stage of casting. Moreover, the height of the formed relief protrusions has a direct impact on the amount of surface roughness. As a result of studies, electrolyte-plasma polishing process modes were established, ensuring the formation of a smooth surface without the presence of embossed protrusions, smoothing the microrelief with the removal of scratches resulting from pre-grinding, achieving a low roughness value (Ra 0.057 micron) and a high reflection coefficient (0.7), which fully meets the requirements for the surface of the implants.

Effect of Electrolytic Plasma Polishing on Surface Properties of Titanium Alloy

“…Compared to other polishing methods, such as electrochemical and mechanical polishing [8][9][10][11], EPPo offers advantages such as no structural selectivity, no macroscopic forces, high processing efficiency, excellent polishing quality, and environmental friendliness. EPPo is particularly suitable for polishing biomedical parts with free-form surfaces or complex geometries such as knee joints, dental implants, and surgical instruments [12]. It can be used not only as a final processing procedure for biomedical parts but also as a pretreatment for thermal spraying [13], ion implantation [14], physical vapor deposition [15], chemical vapor deposition [16], and other processing processes, which has a broad application prospect in the biomedical field.…”

Electrolyte component preference and surface integrity impact analysis for electrolytic plasma polishing of cobalt-chromium-molybdenum alloys

“…Aliakseyeu Y G. et al established an EPP process mode for surface nishing of cobalt chromium alloy implants, which can smooth microrelief while removing scratches generated by pre-grinding. The roughness was reduced to 0.057µm, and the surface re ection coe cient was increased to 0.7, resulting in a smooth and wear free high-quality surface [12]. Thus, EPP technology proves capable of attaining exceptional surface nishes, even for challenging-to-machine high-temperature alloys.…”

Electrolytic plasma polishing of NiTi alloy

“…In addition to surface polishing, the method also provides deburring, cleaning, and increased corrosion resistance of the surface [13]. EPP is widely used in the processes of polishing and surface cleaning of medical devices made of various metallic materials, such as corrosion-resistant steels, titanium alloys, cobalt-chromium alloys [14,15]. However, until now, technological regimes and electrolytes have not been developed for processing nitinol products, including products of small section and rigidity used for minimally invasive endovascular surgery.…”