modeling of sic matrix composite production by cvi process

Modeling of SiC

Composite

Production by CVI

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2016

STR Group

VR Software for Modeling of SiC Matrix

Composite Production by CVI Process

VR™-CVI SiC Edition

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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

Geometry and Computational Mesh

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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, …

Material Properites and Monitoring Solution Progress

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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, …

Material Process and Monitoring Solution Progress

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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.

Example 1: Isothermal CVI (ICVI)

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Example 1: Isothermal CVI Process

Example 2: Thermal-Gradient CVI

Example 3: Forced-Flow CVI

Example 4: Microwave-Heated CVI

ICVI: Computational Model of the ICVI Reactor

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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

ICVI: Meshing

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Fragment of the grid

ICVI: Species Mass Fractions

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MTS mass fraction HCl mass fraction

ICVI: SiC Deposition Rate Inside the Wall

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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

ICVI: Density Evolution

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Total process duration: 355 hours

Initial preform mass: 0.70 kg

Final preform mass: 4.88 kg

Time step is

50 hours

t = 3

50 h

ours

Example 2: Thermal Gradient CVI (TGCVI)

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Example 2: Thermal Gradient CVI




TGCVI: Problem Set Up

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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


Porosity: ε = 0.6


Model of overlapping cylinders is used to describe

structure of the porous medium

TGCVI: Temperature Distribution in the Reactor and Preform

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Temperature distribution in the whole reactor

Temperature distribution in the preform

TGCVI: Material Supply

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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

TGCVI: SiC Deposition Rate

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Fragment of SiC deposition rate distribution at the

bottom of the preform

TGCVI: Material Density

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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

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.

Example 3: Forced-Flow CVI Process (FCVI)

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FCVI: Reactor and Parameters

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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


Porosity: ε = 0.6


Model of overlapping cylinders is used to

describe structure of the porous medium

FCVI: Temperature Distribution

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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.

FCVI: Flow Pattern

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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.

FCVI: Flow Pattern Evolution

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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

FCVI: Evolution of the Material Density

25 t = 0 h t = 90 h t = 180 h t = 270 h t = 360 h t = 460 h

FCVI: Effect of the Flow Rate

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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

Example 4: Microwave-Heated CVI (MWCVI)

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MWCVI: Reactor Design

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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

MWCVI: Flow Pattern in the Reactor

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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


Porosity: ε = 0.7


Density: ρ = 966 kg/m3

MWCVI: Temperature Distribution

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Temperature distribution in the reaction chamber

Detailed temperature distribution in the preform

MWCVI: Material Density Evolution

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t = 0 h

t = 10 h

t = 20 h

t = 30 h

t = 40 h

t = 57 h

ρ, kg/m3

MWCVI: Effect of Temperature on Cycle Length and Material Quality

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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

VR™-CVI SiC Edition

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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

http://www.str-soft.com/contact

