Overview of VR software capabilities for modeling of SiC matrix composite production by chemical vapor infiltration (including examples of ICVI, TGCVI, FCVI, MWCVI). Effects of the flow rates and temperature on density evolution, process duration and resulting material quality are shown.

1. Modeling of SiC
Composite
Production by CVI
1

2. 2016
STR Group
VR Software for Modeling of SiC Matrix
Composite Production by CVI Process

3. VR™-CVI SiC Edition
3
Virtual Reactor for Modeling of SiC Matrix Composite Production
by CVI Process (2016)
Virtual Reactor (VR) was originally developed for the simulation of long-term growth of bulk crystals from
the vapor phase. VR is an easy-to-use tool that can be used by growers with no prior modeling
experience. Now software comes in multiple editions including PVT, HVPE, CVD, MOVPE. While the first
version of the software was released more than a decade ago, edition for CVI SiC was released in 2016
Editions:
VR™-PVT SiC for modeling of SiC growth by sublimation method;
VR™-PVT AlN for modeling of AlN growth by sublimation method;
VR™-CVI SiC
HEpiGaNS™ for Hydride Vapor Phase Epitaxy of GaN, AlN, and AlGaN;
VR™-CVD SiC for modeling of Chemical Vapor Deposition of SiC crystals;
VR™-NE for modeling of epitaxy group-III Nitrides by MOCVD;
VR™-III-V for modeling of epitaxy group-III Arsenides and Phosphides by MOCVD;
VR™-CVD II-VI for modeling of ZnS and ZnSe deposition by CVD

4. Geometry and Computational Mesh
4
For your convenience, input of the shape
outlines can be done both using mouse
and editing coordinates of the elements.
Alternatively, geometry can be imported
from AutoCAD
Automatic grid generation is available
along with multiple options for
optimizing the grid manually.
GUI provides multiple options for fast and
convenient geometry specification, …

5. Material Properites and Monitoring Solution Progress
5
The software comes with a database of
material properties. Materials can be
selected from the list and assigned to the
respective geometry blocks
Solution progress can be monitored
either based on residuals or by observing
evolution of some variable at some
chosen point
… several options of solution control, …

6. Material Process and Monitoring Solution Progress
6
Results can be visualized with built-in
tools to see distribution of the computed
variables over the cross sections
Plots can be built instantly by clicking the
respective line and choosing the variable
of interest
… and built in tools for result visualization.

7. Example 1: Isothermal CVI (ICVI)
7
Example 1: Isothermal CVI Process
Example 2: Thermal-Gradient CVI
Example 3: Forced-Flow CVI
Example 4: Microwave-Heated CVI

8. ICVI: Computational Model of the ICVI Reactor
8
Initial parameters of the preform:
Porosity: ε = 0.7
Bundle diameter: 500 μm
Process temperature: 1050 °C
Pressure: 50 mbar
Flow rate: 2.2 slm
H2:MTS ratio:10:1

9. ICVI: Meshing
9
Fragment of the grid

10. ICVI: Species Mass Fractions
10
MTS mass fraction HCl mass fraction

11. ICVI: SiC Deposition Rate Inside the Wall
11
Distribution of the deposition rate in the bulk of the preform. Note that the results are two
dimensional but they can be presented in more intuitive 3D form using built-in visualization tool

12. ICVI: Density Evolution
12
Total process duration: 355 hours
Initial preform mass: 0.70 kg
Final preform mass: 4.88 kg
Time step is
50 hours
t=350hours

13. Example 2: Thermal Gradient CVI (TGCVI)
13
Example 2: Thermal Gradient CVI
Example 1: Isothermal CVI Process
Example 3: Forced-Flow CVI
Example 4: Microwave-Heated CVI

14. TGCVI: Problem Set Up
14
Parameters:
Pressure in the system: P = 5 kPa
Temperature of the preform: T = 1000 ºC
Initial gas mixture: MTS + H2
Flow rate: F = 200 sccm,
XH2 = 0.95, XMTS = 0.05
Initial parameters of the preform:
Porosity: ε = 0.6
Bundle diameter: 500 μm
Model of overlapping cylinders is used to describe
structure of the porous medium

15. TGCVI: Temperature Distribution in the Reactor and Preform
15
Temperature distribution in
the whole reactor
Temperature distribution
in the preform

16. TGCVI: Material Supply
16
Fragment of the flow pattern at
the lower side of the preform
In computed results, one can see a
directed flow of the gas mixture into
the preform bulk. This flow is
induced by intensive deposition
process inside the porous medium
of the preform and it provides mass
supply for the densification process

17. TGCVI: SiC Deposition Rate
17
Fragment of SiC deposition rate distribution at the
bottom of the preform

18. TGCVI: Material Density
18
Evolution of the
Material Density
with Time
t = 0 h t = 80 h t = 160 h t = 240 h t = 320 h t = 400 h

19. TGCVI: Effect of Temperature on the Final Density and Duration
19
Dependence of final material density and the process duration on temperature
Computations reproduce the well known effect
that at higher temperatures the process becomes
faster but the ultimate quality starts decreasing at
certain temperatures due to the trade off between
the material transport to the preform core and
deposition rate.

20. Example 3: Forced-Flow CVI Process (FCVI)
20
Example 3: Forced-Flow CVI
Example 1: Isothermal CVI Process
Example 2: Thermal-Gradient CVI
Example 4: Microwave-Heated CVI

21. FCVI: Reactor and Parameters
21
Parameters:
Pressure in the system: P = 5 kPa
Temperature of the preform: T = 1000 ºC
Initial gas mixture: MTS + H2
Flow rate: F = 200 sccm,
XH2 = 0.95, XMTS = 0.05
Initial parameters of the preform:
Porosity: ε = 0.6
Bundle diameter: 500 μm
Model of overlapping cylinders is used to
describe structure of the porous medium

22. FCVI: Temperature Distribution
22
Temperature distributions in the whole reactor and
in the preform area are shown in different scales
to better resolve most important features.
Note that VR can be used to automatically fit the
heater power to achieve the goal temperature at
certain point specified by the user.

23. FCVI: Flow Pattern
23
Flow pattern in the reactor will be changing with
changing porosity of the preform. At the
beginning of the process, the gas mixture flows
through the preform along its whole height.

24. FCVI: Flow Pattern Evolution
24
Flow pattern after 300 h of the densification
The pores at the inner surface of the lower part of the
preform are completely plugged with the matrix material
deposited during previous stages of the process. Thus, the
gas mixture does not flow through this part of the preform.
The mixture goes only through the upper part of the
preform.
Some portion of the gas in the external region of the
chamber turns downwards and flows into the outer zones
of the bottom part of the preform providing continued
densification of these zones even after termination of the
through flow

25. FCVI: Evolution of the Material Density
25t = 0 h t = 90 h t = 180 h t = 270 h t = 360 h t = 460 h

26. FCVI: Effect of the Flow Rate
26
T = 1100 ºC
FH2 = 19 sccm
t = 250 h
T = 1100 ºC
FH2 = 2 slm
t = 430 h
For FCVI, flow rate of carrier gas is
an additional parameter affecting the
uniformity of densification.
On the right, the sets of results shows
final density distribution for the flow
rate of H2 increased compared to the
case on the left. Flow rate of MTS is
the same for both cases

27. Example 4: Microwave-Heated CVI (MWCVI)
27
Example 4: Microwave-Heated CVI
Example 1: Isothermal CVI Process
Example 2: Thermal-Gradient CVI
Example 3: Forced-Flow CVI

28. MWCVI: Reactor Design
28
Scheme of the MWCVI reactor
MW heating in the bulk of the preform leads to formation of temperature gradient typical for thermal-gradient modifications of CVI
Lab-scale MWCVI plant. Form Beatrice Cioni and
Andrea Lazzeri, International Journal of Chemical
Reactor Engineering, Vol. 6 (2008) Article A53

29. MWCVI: Flow Pattern in the Reactor
29
MTS + H2
Uniform heat release is specified in the bulk
of the preform to simulate MW heating
Parameters
Preform temperature: 1050 °C
Pressure: 150 mbar
Flow rate: 2.2 slm
H2:MTS ratio:10:1
Initial parameters of the preform:
Porosity: ε = 0.7
Bundle diameter: 800 μm
Density: ρ = 966 kg/m3

30. MWCVI: Temperature Distribution
30
Temperature distribution in the reaction chamber
Detailed temperature distribution in the preform

31. MWCVI: Material Density Evolution
31
t = 0 h
t = 10 h
t = 20 h
t = 30 h
t = 40 h
t = 57 h
ρ, kg/m3

32. MWCVI: Effect of Temperature on Cycle Length and Material Quality
32
T = 1000 °C
T = 1050 °C
T = 1100 °C
T = 1150 °C
T = 1200 °C
ρ, kg/m3
duration: 120 h
duration: 57 h
duration: 34 h
duration: 22 h
duration: 15 h
Dependence of the final material density and the process duration on the temperature

33. VR™-CVI SiC Edition
33
To summarize:
VR is capable of simulating all major physical phenomena in CVI of SiC-matrix
composites;
The tool can be used for optimization of both reactor hardware and the recipe, showing
the effect of temperature and flow rates on the cycle length and material quality;
Software has intuitive user interface, material database and built-in visualization tools,
making the work efficient ;
It does not require prior experience in numerical modeling, moreover, the software was
designed to be used by the researchers and engineers working with the growth
equipment;
Our team provides online customer training and support guiding the user through every
stage of the modeling process when needed
Contact us at www.str-soft.com/contact