Méthodologie d’évaluation des performances anticorrosion pour des couches minces DLC : une approche qualitative et quantitative

figure 1 : Schematic diagram of cathodic protection where steel is the cathode of the system.

figure 2 : Schematic diagram where steel is the anode of the system (coating of noblier metal).

figure 3 : Schematic diagram showing DLC coatings general architecture for mechanical parts.

figure 4 : Stainless steel (left) and steel coated with DLC thin films (right) in contact with with aerated NaCl solution 

figure 5 : Schematic diagram representing a salt spray chamber (extracted from: http://www.climatictestchambers.com).

figure 6 : Our specific samples on dedicated support into the fog cabinet and fog cabinet diagram [10].

Table 1 : Parameters to be set at the beginning.

Table 2 : Parameters to be controlled every 24h.

figure 7 : Comparison of different coupons for PVD/CVD processes.

figure 8 : Curve of sample’s temperature as function of time

figure 9 : Stable microstructure up to 350°C of 100Cr6 heat treated associated with a hardness level of 55 HRC

figure 10 : Polishing apparatus (left) and roughness against thin film thickness (right).

figure 11 : Roughness profiles of (a) mirror-like polished (Ra = 0.01 µm) and (b) polished to Ra = 0.05 µm.

Table 3 : Roughness values for mirror-like and standard polished surface.

figure 12 : Optimized samples holders for PVD/CVD processes in the scope of corrosion tests.

figure 13 : Corrosion coupons (Ø50 mm) masked with colored neoprene resin: edges of exposed surface (left) and non-exposed surface (right).

figure 14 : Cleaning procedure after masking.

figure 15 : Same DLC coated coupon comparison: uncleaned (left) and cleaned (right) samples using ammonium citrate.

figure 16 : Evaluation of corrosion of stainless steel substrates based on pinholes [13].

figure 17 : Cleaning procedure before samples inspection and evaluation.

figure 18 : Reference samples to approximately determine size of pinholes.

figure 19 : Entire surface cleaned of polished 100Cr6 Heat Treat. Ø50 samples coated with various DLC coatings architectures after 24h, 110h and 200h of NSS test

figure 20 : Magnification (x2) of the surface cleaned of polished 100Cr6 Heat Treat. Ø 50 samples coated with various DLC coatings architectures (from left to right : X, Y and Z) after 110h of NSS test (200h samples surfaces are not exhibited due to over-corrosion).

Table 5 : Pinholes sizes categories based on ASTM G46

Figure 21 : Cross-sectional view of a 20 µm diameter pinhole coupled with EDX cartography on a Z sample.

figure 22 : Top surface views of a pre-existing defect coupled with EDX analysis on Z sample.

figure 23 : Schematic diagram representing the corrosion evolution of a defect which create an open channel for electrolyte.

Table 6 : Corrosion behavior of same polished 100Cr6 Heat Treat. Ø50 samples but with various DLC coatings architecture with our corrosion evaluation grid. (E means that samples has been stopped due over-corrosion).