Corrosion study on TiCrN coatings deposited on 316L by RF magnetron sputtering
N. Madaoui 1, *, A. Kehal 2, S. Meriem1, N. Saoula1,
1Division Milieux Ionisés et lasers,
Centre de Développement des Technologies Avancées CDTA Cité du 20 août 1956, Baba Hassen, BP n°17, Alger, Algérie
2Division Couches Minces et Hétérostructures,
Unité de Recherche Matériaux, Procédés et Environnement (UR-MPE) université M’hamed bougara, Avenue de l'Indépendance, 35000 – Boumerdès.
*E-mail : [email protected]
Abstract
-
Titanium-Chromium-nitride (TiCrN) coatings are widely used for cutting tools because of high hardness and superior resistance to a corrosion.Titanium-Chromium-nitride coatings on 316L stainless steel can be used to extend their life cycle.
TiCrN coating was prepared by RF magnetron sputtering, and their corrosion resistance was investigated. TiCrN coatings were successfully prepared by reactive RF magnetron sputtering method, on 316L stainless steel substrate.
potentiodynamic polarisation test was conducted in an aerated (3.5% weight) NaCl solution. During the test, the TiCrN coatings show the lowest corrosion current density and the highest polarization resistance.
Consequently, it was found that the 316L stainless steel coated with the TiCrN coating had an improvement in corrosion resistance in 3.5% NaCl solution at room temperature.
Keywords
:
Corrosion behavior; RF magnetron sputtering; TiCrN; coatings; 316L stainless steel.I. INTRODUCTION
In this study, the TiCrN coatings were prepared by RF magnetron sputtering, and the microstructural evolution and their corrosion resistance was investigated.
Usually, Ti–Cr–N coatings have been grown by Among various surface modification methods like reactive sputtering (RSP) [1], ion-beam assisted deposition (IBAD) [2,3], cathodic arc deposition [4,5], electroplating [6] and electrochemical surface nitriding [7],.. etc.
However, other low temperature processes like the physical vapor deposition (PVD) has been used successfully to extend the applications of substrate
materials. The PVD technique has been used widely due to its high deposition rate and good adhesion strength [8]. The aim of this work is to understand the role of TiCrN-coating on corrosion behavior of stainless steel by electrochemical measurements, immersion investigation and microstructure analysis, comparing with a stainless steel incoating.
The coatings were tested in 3.5% NaCl solutions.
The coating of Titanium-Chromium-nitride was deposited by RF pulverization of Cr/Ti under a argon and nitrogen atmosphere.
II. EXPERIMENTAL PROCEDURE
2.1
Preparation of coatings by RF sputteringThe 316 L stainless steel was used as a substrate.
All substrates were finely polished to 1 µm, and then ultrasonically cleaned in acetone for 10 min.
The experimental parameters of the deposition process are shown in Table 1
TABLE 1: OPERATING PARAMETERS OF RF MAGNETRON SPUTTERING.
2.2
Corrosion behaviorThe corrosion resistance of TiCrN coatings was evaluated by potentiodynamic polarization test using a PARSTAT 4000. The working cell was a standard three-electrode cell having a high-purity graphite rod as a counter electrode and a saturated calomel electrode (SCE) as a reference electrode. 6 h of immersion was allowed to ensure steady-state conditions. For potentiodynamic polarization experiments, the potential was scanned at a scan rate of 1 mV/s.
The corrosion tests were performed in 3.5% NaCl solution under free air condition at room temperature. Prior to corrosion test, all samples were cleaned with distilled water before loading the sample to the Tafel sample holder. The Tafel plot was obtained after the electrochemical measurements. The Ecorr (corrosion potential) and icorr (corrosion current density) were deduced from the Tafel plot using instantaneous Tafel-type fit Versa Studio corrosion analysis software. All the potentials in this paper are reported in the SCE scal.:
icorr = [ babc/ 2.303(ba+bc) ]1/Rp (1)
Where ba and bc are the Tafel slopes or the Tafel constants, expressed in V/decade, and Rp is the polarization resistance expressed in K·cm2. The polarization resistance is calculated using the following equation:
Rp=(∆E/∆I)|∆E-i (2)
Where ∆E is the polarization potential and ∆I is the polarization current. If the polarization resistance increases the corrosion current decreases [9]
III. RESULTS AND DISCUSSION
Fig. 1 shows the polarization curves (Icorr. vs.
Ecorr.) for the stainless steel substrate, and TiCrN coatings tested using 3.5 wt.% NaCl solution at room temperature. Note that the stainless steel substrate exhibited a corrosion current density of 63,015 mA/cm2 and that the corrosion resistance was improved after depositing of TiCrN coatings.
Icorr. for TiCrN coatings were 2.32 (0V), 13.643(- 25V), 17.203(-50V), 682.88(-75V) and 39.412(-100V) mA/cm2, respectively. In addition, corrosion rate can be examined by the corrosion current density (i.e., Icorr.). Icorr. can be used as an indicator to evaluate the kinetics of corrosion resistance and calculated by the Tafel equation [10].
The smaller corrosion current density is an indication of excellent corrosion resistance [11].
The TiCrN (0V) coatings exhibited the best corrosion resistance when evaluated by the polarization test.
Parameter Value
Base pressure/ Torr 10-6 Working pressure/
Torr
3.0 10-2
Substrate stainless steel Target (d 100 mm)
(99.95%)
Cr/Ti (80/20)%
Gas mixture/ (sccm) Ar: 6 (99.999%), N2: 2 (99.999%)
RF power/W 200
Distance of cathode to substrate/ mm
50
Sustrat polarization 0,-25,-50,-75,-100
-14 -12 -10 -8 -6 -4 -2 -0.6
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8
-75 V
-100 V
uncoated 316L 0 V
-25 V -50 V
Potentiel,(V) (mV/ECS)
Current density , (I) Logi
(A.cm
-2)Fig. 1: Polarization curves of the stainless steel coated and uncoated in 3.5% NaCl solution, obtained at 25 ° C.
TABLE 2: ELECTROCHEMICAL PARAMETERS OF STAINLESS STEEL AND COATINGS EXPOSURE TO 3.5 WT%NACL AT 25°C.
Alloys Ecorr
(mV/ECS)
Icorr
(nA/cm2)
Rp
(K)
Cr (mpy) Stainless
Steel
-228,279 63,015 623,382 0,187
0V -182,133 2,32 31,464 E3 0,003 -25V -87,894 13,643 7,012 E3 0,016 -50V -280,212 17,203 1,764 E3 0,066 -75V -172,977 682,88 463,465 0,095 -100V -222,4 39,412 997,374 0,118
IV. CONCLUSION
TiCrN coatings have been deposited on stainless steel by means of the magnetron sputtering method.
These coatings improve the corrosion resistance of stainless steel in NaCl solution with 3.5%Wt.
1. The protective properties of the coatings depend on the bias voltage. The best
protective properties were shown by a TiCrN coating with lower polarization.
The best corrosion resistance was found for stainless steel at 0Volt.
2. The TiCrN coating (-25 Volt) and TiCrN coating (-50 Volt) both provided excellent protection for the stainless steel substrate, but much lower icorr for the TiCrN coating which deposited a (0 Volt) indicated the better protection provided for the stainless steel substrate.
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