The influence of chromium as a diffusive additive in the boronizing treatment of AISI 4140 steel on the corrosion resistance of the coating evaluated by Electrochemical Impedance Spectroscopy (EIS)

Dimitrios I Zagkliveris,Georgios K Triantafyllidis,Efstathios Ntovinos,Azarias Mavropoulos,G Mansour,D Tzetzis,P Kyratsis

doi:10.1051/matecconf/202031801040

Dimitrios I Zagkliveris, Georgios K Triantafyllidis + Show 5 more

Open Access

https://doi.org/10.1051/matecconf/202031801040

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Abstract

A large variety of protective coating is being used in industrial applications to improve the resistance of the metallic substrates against corrosion. The pack-cementation method for boronizing and borochromizing is effective to produce extremely hard and corrosion resistant thick coatings and, additionally, is a low-cost and simple technique. In the present study, AISI 4140 steel specimens underwent boronizing and afterwards chromizing by the pack-cementation method using B4C as boron source and Fe-Cr as chromium source, respectively. In both treatments the appropriate activators were used. After chromizing the boronized substrate, a mixed boride phase FeCrB was formed, as it was confirmed by X-ray Diffractometry (XRD). The boronized and the borochromized specimens were subjected to Electrochemical Impedance Spectroscopy (EIS). From the analysis of the frequency response of the coating systems (Bode and Nyquist display), the conclusion that the borochromized specimens were significantly more corrosion resistant was extracted. Finally, data of optical and electron microscopy contribute to the validity of the conclusions.

Highlights

A plenty of technical applications demand the utilization of materials that withstand intense wear and corrosion conditions such as frictional contact with other hard components and interaction with corrosive environments, probably in a wide temperature range.One of the mostly effective ways for superficial protection of many metallic materials against the above referred destructive conditions is the boronizing treatment
It is experimentally shown that the addition of another metallic element in the boride layer could result in an increase of the plasticity of the coating [4]
In the preliminary stage of the study, specimens of AISI 4140 steel were boronized and half of them underwent chromizing. Both thermochemical treatments were carried out using the pack cementation technique

Summary

Introduction

A plenty of technical applications demand the utilization of materials that withstand intense wear and corrosion conditions such as frictional contact with other hard components and interaction with corrosive environments, probably in a wide temperature range. It is experimentally shown that the addition of another metallic element in the boride layer could result in an increase of the plasticity of the coating [4] Another significant advantage, especially when chromium is used as additive, is the improvement of the resistance of the coating against corrosion [5]. Experimental studies on chromizing a boronized steel (boronizing + chromizing) [6-8], boronizing a chromized steel (chromizing + boronizing) [9,10] and the simultaneous borochromizing [11-13] are referred in the literature In some of these cases, the examined property of the borochromized materials was resistance against friction [6,10] and the corrosion resistance [12]. Their score in EIS method was compared with the boronized specimens. The last decade EIS became a valuable method for evaluating the corrosion resistance of boride [14] and other types of coatings on metallic materials [15-18]

Materials & methods

Results & discussion

Electrochemical Impedance Spectroscopy

Conclusion