1. MECHANICAL PROPERTIES OF WC-25/17/12Co CERMETS SPRAYED BY HVOF AND CGS
Dr. Miguel Couto
Dr. Irene García-Cano
Dr. Sergi Dosta
Dr. Amadeu Concustell
Dr. Núria Cinca
Prof. J.M. Guilemany
11/5/2015

2. CONTENTS The Cold Gas Spray Process;
Powder and coatings characterization:
WC-25Co;
WC-17Co;
WC-12Co.
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);
Erosion tests (G76-04);
Fracture toughness.
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. EXPERIMENTAL PROCEDURE
Gas pressure (bar)
Distance (mm) 40 20 10 35 30
It is a very important step of the work in progress because it will allow determining if the chosen process parameters were the most effective and then optimizing them, also it will provide the knowledge to understand if this process brings in fact more advantages and efficiency when compared to other conventional thermal spray techniques.
For low carbon steel and Al7075 there were different spraying conditions.
In some cases, namely the spraying of WC-12Co onto Al7075, an extra variable was added – a pre-chamber that allows more time of heating for the powder before spraying providing extra ductility and particle velocity.

6. HVOF DESIGN OF EXPERIMENTS
EXPERIMENTAL PROCEDURE
HVOF DESIGN OF EXPERIMENTS
Fuel gas / d (mm)
150
175
200
225
250
275 H2 C
Propylene C

7. POWDER CHARACTERIZATION WC-25Co FREE SURFACE + CROSS SECTION
Figure 2 – WC-25Co SEM free surface, at 750x, cross section, at 1500x, and FE-SEM micrographs at 5000x micrographs, where the near nanosized carbides can be seen.

8. POWDER CHARACTERIZATION WC-25Co XRD + LS ANALYSIS
Figure 3 – WC-25Co powder’s Laser Diffraction and X-Ray Diffraction results.

9. POWDER CHARACTERIZATION WC-17Co FREE SURFACE + CROSS SECTION
Figure 4 – WC-17Co SEM free surface, at 750x, cross section, at 1500x, and FE-SEM micrographs at 4500x micrographs, where the near nanosized carbides can be seen.

10. POWDER CHARACTERIZATION WC-17Co XRD + LS ANALYSIS
Figure 5 – WC-17Co powder’s Laser Diffraction and X-Ray Diffraction results.

11. POWDER CHARACTERIZATION WC-12Co FREE SURFACE + CROSS SECTION
Figure 6 – 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.

12. POWDER CHARACTERIZATION WC-12Co XRD + LS ANALYSIS
Figure 7 – WC-12Co powder’s Laser Diffraction and X-Ray Diffraction results.

13. COATINGS CHARACTERIZATION WC-25Co ONTO Al7075-T6
Avg. Thickness = 211±24µm
Avg. HV300 = 848±55
Deposition Efficiency ≈ 24%
Figure 8 – WC-25Co SEM micrographs of the best coatings obtained onto Al7075-T6 substrate.

14. SPLATS WC-17Co ONTO Al7075-T6
Figure 9 – WC-17Co splats obtained onto Al7075-T6.

15. SPLATS WC-17Co ONTO Al7075-T6
Figure 10 – WC-17Co splats obtained onto Al7075-T6.

16. COATINGS CHARACTERIZATION WC-17Co ONTO Al7075-T6
Avg. Thickness = 129±5µm
Avg. HV300 = 1223±59
Deposition Efficiency ≈ 14,2%
Figure 10 – WC-12Co SEM micrographs of the best coatings obtained onto Al7075-T6 substrate.

17. COATINGS CHARACTERIZATION WC-12Co ONTO Al7075-T6
Avg. Thickness = 93±8µm
Avg. HV300 = 1419±93
Deposition Efficiency ≈ 12%
Figure 10 – WC-12Co SEM micrographs of the best coatings obtained onto Al7075-T6 substrate.

18. COATINGS CHARACTERIZATION XRD OF THE COATINGS VS POWDER
Figure 11 –X-Ray Diffraction results of a representative WC-17Co coating vs WC-17Co powder.

19. RUBBER-WHEEL TESTS -10% 62% 133% *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.

20. BALL-ON-DISK (25N) TESTS

21. BALL-ON-DISK TESTS
-8% 9%
145%

22. EROSION TESTS 6% 8%
10%

23. ELECTROCHEMICAL TESTS
-106%
101%
140%

24. FRACTURE TOUGHNESS TESTS
E – Young Modulus (Marshall and Evans)
Hv – Vickers hardness (1000gf)
KIC CGS = 8,7 ± 0,2 MPa/m2 VS
KIC HVOF= 5,1 ± 1,6 MPa/m2
71% gain

25. FRACTURE TOUGHNESS TESTS
71%
24%
10%

26. CONCLUSIONS
WC-25Co had an erosion resistance improvement of approximately 6,7%, WC-17Co of 6,9%; and WC-12Co of 9,5%, when compared to WC-12Co by HVOF;
CGS WC-25Co coatings showed a gain of 41% in fracture toughness when compared to WC-12Co HVOF, with WC-17Co having an improvement of 24% and WC-12Co by CGS of 9%;
CGS coatings showed – when compared to the benchmark coatings sprayed by HVOF – less intensity of corrosion after the kinetic electrochemical tests meaning that their corrosion rates are slower and therefore will resist for a longer period of time to extreme corrosion environments.

27. MECHANICAL PROPERTIES OF WC-25/17/12Co CERMETS SPRAYED BY HVOF AND CGS
Dr. Miguel Couto
Dr. Irene García-Cano
Dr. Sergi Dosta
Dr. Amadeu Concustell
Dr. Núria Cinca
Prof. J.M. Guilemany
11/5/2015