An electrochemical study of the corrosion resistance of boride coating obtained by thermo-reactive diffusion
Introduction
The use of hard coating to improve surface layer properties is a method for protecting substrate from environmental effects. The hard coatings have high hardness, low coefficient of friction, low porosity, high corrosion and adhesive wear resistance [1].
Using of hard coating to produce wear resistant surface layer that can increase the durability of the equipment is now well accepted [2], [3], [4]. Hard coating of nitride, carbide, boride and carbonitride of transition metal are extensively used to improve the wear resistance of ferrous materials [5], [6]. Also, the wear, the microhardness and the micro-abrasive properties of nitride, carbide, boride and carbonitride coatings on the steel-substrate were studied [7], [8], [9], [10], [11].
Hard coatings have been produced by lots of coating techniques such as CVD, PVD and thermo-reactive diffusion (TRD). TRD is a method for coating steel with a hard, wear resistant layer of carbides, nitrides and boride. In this process, elements such as carbon, nitrogen and boron are surfaced into deposited layer to form a dense and metallurgically bonded carbide, nitride or boride coating at the substrate surface [12]. TRD process and its advantages over other deposition techniques have been extensively reviewed [13].
The coatings on the substrate improve the performance of cutting equipments which are used in industry. Because of higher hardness of boride layers, in the range of 1400–2100 HV [14], these layers are appropriate choices to increase the durability of cutting tools.
When cutting tools with boride coatings are used in corrosive environment such as sanitary and food industries, aggressive ions can attack the surface layer and corrosion occurs.
Providing coating layers have porosity, aggressive ions can penetrate through coating and subsequently corrode the metal's bare surface. The formation of oxide on the surface results in blunting the cutting tools and decreasing their durability. The corrosion resistance properties of hard coating especially boride coating are studied less frequently than mechanical properties.
However, boride layers on some steels were investigated by previous papers [15], [16]. In these investigations, the corrosion resistance properties of hard coating have been studied only by current density-potential measurements. The use of electrochemical impedance spectroscopy method and modelling of their data are powerful methods for investigating corrosion resistance.
The aim of this study is to investigate the corrosion resistance of boride coating on three kinds of steels with variable manganese element by Tafel polarisation and electrochemical impedance spectroscopy (EIS). Furthermore, the porosity of this coating, formed by TRD process, is examined by data which is extracted from electrochemical impedance spectroscopy.
Section snippets
Materials
The three kinds of steels used in this investigation, were produced precisely according to their chemical composition for a special work. The chemical compositions of these steels are given in Table 1. These steel compositions have exactly been controlled so as to achieve the steel with minimum amount of impurity such as sulfur, phosphorus, etc. The test samples were cut from the above-mentioned steels in rectangular shape with 10 mm × 10 mm × 8 mm dimensions. These samples were polished using
Composition and morphology of the boride coating
Boron atoms have relatively small size and high mobility, therefore, they can easily diffuse into ferrous alloys, forming FeB and Fe2B intermetallic.
The X-ray diffraction patterns of the borided steels coated in the mentioned bath are given in Fig. 1. It can be seen that the layers are made up of Fe2B, FeB, MnB and Mn2B depending on the kind of steel. The layers were formed by the chemical combination of Fe or Mn atoms in the substrate with boron atoms dissolved in bath. Steel samples labeled
Conclusions
The corrosion behaviour of boride layer on the three kinds of steel (with differing Mn contents) has been studied with Tafel polarisation and electrochemical impedance spectroscopy. The following conclusions can be assumed:
- (a)
The values of corrosion current density show that the addition of manganese element decreases the corrosion rate.
- (b)
The corrosion potential (Ecorr) of S3 steel is generally more positive than S2 and S1 steel suggesting that the durability of the coating on the S1 and S2 steels
References (25)
Materials and Design
(2005)- et al.
Wear
(1997) - et al.
Wear
(1998) - et al.
Wear
(1995) Materials Chemistry and Physics
(2004)- et al.
Surface and Coating Technology
(2006) - et al.
Journal of Materials Processing Technology
(2003) - et al.
Applied Surface Science
(2006) - et al.
Surface and Coating Technology
(2005) - et al.
Materials Science and Engineering A
(2003)
Surface and Coating Technology
Surface and Coating Technology
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