1. 3D MULTICOMPONENT MODEL FOR COLD SPRAY TITANIUM PARTICLES
16th February 2016, Nashville, Tennessee, USA
Muhammad Faizan-Ur-Rab1,2
S. H. Zahiri2, S. H. Masood1, M. Jahedi2, R. Nagarajah1
Swinburne University of Technology1 / CSIRO2 Melbourne, Australia

2. Outline Cold Spray Process Additively Manufactured Parts Advantages
Need for 3D Model
3D Multicomponent Model
Titanium Particles Injection
3D Model Outcome
Conclusion

3. Schematic diagram of Cold Spray process
Cold spray is a solid state rapid deposition process. In this process powder particles accelerate to the velocities well above supersonic speeds
( m/s) in order to establish coatings on the surface of substrate.
This is a schematic diagram of cold spray process. As you can see here that High Pressure Low velocity Gas passing through heater enters into the convergent section of de Laval nozzle carrying powder particles and leave the nozzle with a supersonic speeds of Mach no greater than 1 as Low Pressure High Velocity gas. After exiting from the nozzle the particles impact on a substrate surface with a supersonic speed and deposited over the surface. phenomenon.
Schematic diagram of Cold Spray process

4. Cold Spray Deposition Cold Spray Particles:
substrate
P0,
r0, T0
Throat, M=1
M>1
M<1 np ng
Cold Spray Particles:
Accelerated through a supersonic de Laval nozzle
Critical Velocity of particle
Impact onto a substrate:
Deformation
Adhesion
The cold spray deposition occur when particles accelerated through supersonic de Laval nozzle reach to the certain velocity called critical velocity.
It is different for different materials.
Particles at critical velocity after impact plastically deformed and bonded onto the substrate surface.
The deposition occur in nano-seconds.

5. Cold Spray additively manufactured parts
Unsprayed powder particles
Single particle splat
Multiple particle impacts
These are the electron microscope images of unsprayed spherical titanium powders before impact, single particle impact and multiple particle impact.
And these are the few examples of additively manufactured cold spray parts including titanium ring, a titanium valve, circular disk and tensile specimen.
Courtesy: CSIRO Cold Spray Lab

6. Advantages Solid state deposition process No melting Low oxide content
Low thermal stresses
Variety of materials can be sprayed
No size limitations
No atmospheric protection or vacuum chamber
Large, free-standing components of various geometries can be manufactured
Deposition rates of tens of kilograms per hour are possible

7. Need for a Cold Spray 3D Model
1D or 2D models are incapable of representing the Cold Spray process holistically.
1D and 2D models results are particularly unreliable under extreme cold spray conditions such as high temperature and pressure.
3D model is an accurate and cost-effective virtual tool for industry to study process outcome before conducting actual experiments.
Available 1D

8. 3D CFD Multicomponent Model
Coupling of nitrogen with air (realistic design)
Use of k-ε turbulence model
New values of k-ε turbulence model coefficients CЄ1 , CЄ2 and Prandtl no (Pr) suggested
CЄ1 = 1.65 (1.44), CЄ2 = 2.30 (1.92), Pr = 0.3 (0.9)
Multicomponent means coupling high pressure nitrogen with air.
For development of 3D multicomponent model, two equation k-epsilon turbulence model is chosen because of it is robustness in achieving numerical convergence, economical in cost, commercially available and operative on desktop PC instead of requiring supercomputers.
It’s a good comprise between numerical accuracy and overall computation time. It can produce results within 15% acceptable error range.
The uniqueness of this study is the introduction of new values of turbulence coefficients. These new values are suggested after calibrating and validating the model outcome with experimental results. The new values predicted the cold spray model outcome with consistency and realistically.
The new values of turbulence coefficients for cold spray process are 1.65 and 2.30 contrast to default values of 1.44 and 1.92 suggested for turbulence flow.

9. Multicomponent Model - Development
(a)
(b)
Cold Spray (a) 3D geometry of all domains and (b) hexa mesh developed for CFD multicomponent model.

10. Multicomponent Model - Calibration
Figure a is showing the experimental setup to record substrate temperature with the help of 5 thermocouples placed diagonally from the center on the rear side of the substrate.
This is a substrate temperature curve showing the outcome of 3D model calibration for cold spray condition 1 which is 550C and 1.4MPa.
On x-axis, the distance from the substrate center is plotted and Y-axis showing the temperature.
The black stars are showing the temperature recorded by 5 thermocouples and the indigo curve is showing the temperature on surface of substrate estimated by the developed 3D multicomponent model.
The overall difference between experimental data and model outcome is within 15% which is quite promising.
Cold Spray (a) Experimental set-up to record substrate temperature with 5 thermocouples and (b) comparison with 3D model for cold spray condition at 550°C, 1.4MPa.

11. Multicomponent Model - Validation
This is a substrate temperature curve showing the outcome of 3D model validation for cold spray condition 2, at 800C and 3MPa which is higher than the previous condition 1.
The 3D model with new turbulence coefficient successfully estimated the substrate temperature and the temperature difference between 3D model and experimental measurement is within 15%.
Estimated temperature profile of impinging Cold Spray jet on surface of substrate at 800ºC, 3 MPa.

12. Titanium Particles Injection
After validating the 3D multicomponent model for cold spray jet, titanium particles were injected into the pre-chamber section of cold spray nozzle. The location of injected particle in the model approx. same as the location of powder feeder in the cold spray lab equipment.
This is the actual particle size distribution of the commercially purity (CP) titanium powder used in the cold spray experiment.
In the developed 3D multicomponent model CFD code, this actual particle size distribution was written for the random injection of particles.
You can see the particle ranges from 8 to 80 micron diameter and the highest is the 27 micron diameter.
Distribution of particle size for commercial purity (CP), grade 4 titanium powder used for 3D Cold Spray model.

13. Model Outcome - Particle Velocity
This is the outcome of validated 3D multicomponent model for in-flight particles velocity holistically from the injection point to the moment of impact.
Particles were injected into the validated 3D model for two cold spray conditions.
Figure (a) is showing the particle velocities for cold spray condition 800 C, 3MPa and Figure (b) is showing the particle velocities for cold spray condition 550C and 1.4MPa.
Initially for 800C,3MPa cold spray condition, 2500 particle were injected and then an increased no of 5000 particles were introduced for 550C and 1.4MPa cold spray condition. This is done to show the capability of 3D model. Further validation w.r.t to in-flight particle stat is under study at the moment.
You can see the spread of particles is narrower or more focussed for 800C,3MPa condition as compared to 550C,1.4MPa where particle are relatively more spreaded.
Titanium particle velocity holistically from injection point to the location of impact, (a) 800°C, 3 MPa (b) 550°C, 1.4 MPa.

14. Model Outcome - Particle Temperature
This is another interesting outcome of 3D model related to thermal history of inflight titanium particles.
Figure (a) is showing the particle temperature for 800C, 3MPa cold spray condition while Figure (b) is showing the particle temperature for 550C,1.4MPa cold spray condition.
As you can see in Figure (a) the temperature of particle at the moment of impact is within the range of 300 to 700 C for 800C,3MPa and for 550C,1.4MPa the temperature of particles at the moment of impact is within 200 to 400 C.
The 3D model is reporting an important info regarding temperature of individual particle just before the impact which we can not find in previous 1D or 2D cold spray models. These studies rely on assuming the particle temperature.
Titanium particle temperature holistically from injection point to the location of impact, (a) 800°C, 3 MPa (b) 550°C, 1.4 MPa.

15. Model Outcome - Particle Temperature
This figure is showing a thermal history of 25 and 40 micron particles for cold spray condition 800C, 3 Mpa holistically from injection point to the moment of impact.
The 3D model is reporting an important info regarding temperature of individual particle just before the impact which we can not find in previous 1D or 2D cold spray models. Previous studies rely on assuming the particle temperature.
25µm and 40µm particle thermal history from injection point to the moment of impact for 800°C, 3 MPa.

16. Model Outcome - Particle Temperature
This figure is showing a thermal history of 25 and 40 micron particles for cold spray condition 550 C and 1.4 MPa holistically from injection point to the moment of impact.
3D model can predict the state of individual particle of different size which might be difficult or relatively quite expensive to achieve through experiment.
Cold Spray 3D model is an economical solution for individual particle study.
25µm and 40µm particle thermal history from injection point to the moment of impact for 550°C, 1.4 MPa.

17. Model Outcome - Particle Location
2 mm
3 mm
6 mm
5 mm
Another important information that we can get from 3D cold spray model is the location of particles just before the impact.
Figure (a) is showing the expected location of particle just before the impact for 800C, 3MPa cold spray condition and figure (b) is showing the particle location population for 550C, 1.4MPa cold spray condition along the nozzle central axis.
Now by looking at both figures we can extract three important info. for cold spray particle deposition.
No 1. The spread of particles for 800C,3MPa cold spray condition is more narrow or small as compared to the 550C,1.4MPa cold spray condition.
No2. The particle deposition is asymmetric instead of symmetric in reality. For instance for 800C,3MPa the cold spray jet is shifted to 3 mm left side and 2mm right side from the jet center. Similarly, you can observe this asymmetric behaviour quite large for 550C and 1.4MPa cold spray condition. Here the particle jet is shifted 5mm to the left and 6mm to the right from the jet center.
And No3. is that maximum particle particles are expected to be deposit at the center or core of the cold spray jet.
The previous 1D or 2D model are unable to reveal this information and therefore these studies explain the symmetric particle deposition behaviour.
Estimated location of particles just prior to impact (a) 800°C, 3 MPa (b) 550°C, 1.4 MPa.

18. Concluding remarks
Developed a 3D multicomponent model for Cold Spray using new turbulence coefficients.
Capable of predicting the in-flight particle velocity, temperature and impact location.
Benefit to industry – virtual study of particle state prior to actual cold spray operation.

19. Thanks
Q & A