1. SPRAYING OF A WC-12Co CGS LAYER OVER A WC-Co HVOF COATING
Dr. Miguel Couto
Dr. Sergi Dosta
Dr. Irene García-Cano
Dr. Amadeu Concustell
Dr. Núria Cinca
Prof. J.M. Guilemany
22/6/2015

2. CONTENTS The Cold Gas Spray Process;
Powder and coatings characterization:
CGS WC-12Co powder
HVOF WC-12Co powder;
Dual WC-12Co coating.
Mechanical tests of the obtained optimum coatings:
Rubber-wheel (ASTM C65-00);
Ball-on-disk tests (ASTM G99-04; 15 and 25N; WC-12Co counterpart);
Electrochemical tests of the obtained optimum coatings.

3. COLD SPRAY PROCESS Technique HVOF CGS Energy type Kinetic + Thermal
supersonic velocities
Primeiro trabalho usando N2 como process gas com sucesso.
particle size [5; 50] μm
preheated gas (He, N2, mix) [300; 800]ºC
gas temperature [-100; 100]ºC
Figure 1 – Schematic diagram of the cold spray process.

4. ADVANTAGES Low porosity; No oxidation;
Peening effect (compressive residual stresses);
Initial particle material’s proprieties are retained;
Minimum thermal input to the substrate  temperature-sensitive substrates.

5. POWDER CHARACTERIZATION CGS WC-12Co FREE SURFACE + CROSS SECTION
Figure 2 – WC-12Co SEM free surface, at 750x, cross section, at 1000x, and FE-SEM micrographs at 4000x micrographs, where the near nanosized carbides can be seen.

6. POWDER CHARACTERIZATION CGS WC-12Co XRD + LS ANALYSIS
Figure 3 – WC-12Co powder’s Laser Diffraction and X-Ray Diffraction results.

7. COATINGS CHARACTERIZATION WC-12Co Dual
Avg. Thickness total = 252±14µm
Avg. Thickness CGS layer = 142±10µm
Deposition Efficiency ≈ 24%
Adhesion ≥ 50±4MPa
Figure 4 – WC-12Co Dual SEM micrographs.

8. COATINGS CHARACTERIZATION XRD OF THE COATINGS
Figure 5 –X-Ray Diffraction results of a Dual coating.

9. RUBBER-WHEEL TESTS *WC-12Co
The good distribution of WC carbide particles in the metallic Co matrix and the homogeneous and sub-micrometric size of the carbide particles, without detrimental brittle phases, led to high abrasion resistance.
With an increase of hard WC particles there is an increase in both abrasive and adhesive/friction wear resistance and electrochemical corrosion resistance.
Considering the coatings’ resistance to abrasive wear there was an improvement of 10% for WC-25Co by CGS, 62% for WC-17Co and 133% for WC-12Co coatings by CGS. CGS WC-25Co coatings show similar abrasive wear rate results than WC-12Co coatings by HVOF.

10. BALL-ON-DISK TESTS

11. BALL-ON-DISK TESTS

12. ELECTROCHEMICAL TESTS

13. CONCLUSIONS
It was possible to obtain Dual WC-12Co coatings by spraying two different layers; one by High Velocity Oxy-Fuel and the other by Cold Gas Spray;
After spraying, no microstructural changes, decarburization or formation of fragile η phases were observed, meaning that the bulk properties of the powder were maintained;
The coatings showed good adherence both on the substrate/HVOF interface as well as on the HVOF/CGS interface with adherence values of over 50MPa;

14. CONCLUSIONS
The good distribution of WC particles in the Co matrix that were present in the CGS layer led to high abrasion and friction resistance;
An increase of almost 3.5 times in electrochemical resistance was achieved when testing the Dual coatings, when compared to WC-12Co CGS coatings;
Dual coatings had a deposition efficiency of 24%, meaning an increase of 10% more when compared to WC-12Co CGS coatings.

15. SPRAYING OF A WC-12Co CGS LAYER OVER A WC-Co HVOF COATING
Dr. Miguel Couto
Dr. Irene García-Cano
Dr. Sergi Dosta
Dr. Amadeu Concustell
Dr. Núria Cinca
Prof. J.M. Guilemany
22/6/2015