The Influence of Surface Condition on the Electrochemical Properties of ASTM F138 Steel for Biomedical Applications

Fernando Michelon Marques,Rodrigo Cardoso Costa,Jane Zoppas Ferreira,Alexandre Da Silva Rocha,Giovanni Rocha Santos,Mario Wolfart Junior

doi:10.1590/1980-5373-mr-2020-0062

Abstract

The aim of this paper was to determine the influence of machining parameters on the surface layer, and consequently on the electrochemical properties, of ASTM F138 austenitic stainless steels. Eight different surface conditions were generated in cylindrical samples by turning and polishing. The surface was characterized by surface roughness Ra and Rt, Vickers microhardness and microstructural characteristics. Cyclic voltammetric tests were performed to evaluate the potential of repassivation and pitting. The surfaces were analyzed by Scanning Electron Microscopy after the electrochemical tests were performed. The cutting parameters were identified to have a significant influence, and the feed rate was as influential as the depth of cut. The use of polishing alone is not sufficient to ensure that a surface has good surface integrity. Even with the polishing application, usually used to produce prostheses, a significant reduction in corrosion resistance occurs if care is not taken to minimize surface machining damage. Corrosion resistance is lower and pitting nucleation is higher in the samples with no polishing and with more severe machining parameters. The tests indicated that softer machining parameters can contribute to an increase in the life of implantable components, reducing the probability of localized corrosion, as well as improving the mechanical properties of prostheses.

Highlights

Austenitic stainless steels are widely used in the biomedical area for manufacturing prostheses, orthotics for orthopaedic and orthodontic corrections, surgical instruments and surgical peripherals
Austenitic stainless steels have low thermal conductivity when compared to low alloy steels or bonded steels. They are susceptible to microstructural changes due to thermal and shear action during the machining process, since heat dissipation decreases through the workpiece[2]
Heat generated during the cutting process can be reduced by using coated tools along with lubricating fluids

Summary

Introduction

Austenitic stainless steels are widely used in the biomedical area for manufacturing prostheses, orthotics for orthopaedic and orthodontic corrections, surgical instruments and surgical peripherals. Austenitic stainless steels have low thermal conductivity when compared to low alloy steels or bonded steels They are susceptible to microstructural changes due to thermal and shear action during the machining process, since heat dissipation decreases through the workpiece[2]. The microstructural changes of ASTM F138 stainless steel can be attenuated Such coolants can contaminate the machined area of the workpiece and peripherals of the surface subject to the machining process, requiring further cleaning processes. For Austenitic stainless steels are considered the most difficult materials to process due to the fact that they cause excessive premature tool wear and because it is very difficult to obtain a satisfactory surface finish for the respective processes through which they are submitted[6,7]. Machined surfaces with low roughness values present higher resistance to localized corrosion due to smaller valleys and peaks where oxides form

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