Chemical vapour infiltration (CVI) is a ceramic engineering process where reactive gases are used to infiltrate matrix material into fibrous preforms at elevated temperatures, forming fiber-reinforced composites. During CVI, the preform is exposed to a mixture of carrier gas and matrix material in a reactor at high heat, which causes a chemical reaction depositing the matrix within the preform pores. CVI can produce carbon-carbon composites and ceramic matrix composites like carbon-silicon carbide and silicon carbide-silicon carbide.

2. INTRODUCTION
 Chemical vapour infiltration (CVI) is a ceramic engineering process whereby matrix
material is infiltrated into fibrous preforms by the use of reactive gases at elevated
temperature to form fiber-reinforced composites.
 The earliest use of CVI was the infiltration of fibrous alumina with chromium
carbide CVI can be applied to the production of carbon-carbon composites and ceramic
matrix composites
 A similar technique is chemical vapour deposition (CVD), the main difference being
that the deposition process of CVD is on hot bulk surfaces, while the deposition
process of CVI is on porous substrates.
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3. WORKING PROCESS ?
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4.  During a chemical vapour infiltration process the fibrous preform is supported on a
porous metallic plate through which a mixture of carrier gas along with matrix material
is passed at an elevated temperature
 The preforms can be made using yarns or woven fabrics or they can be filament wound
or braided three-dimensional shapes
 Here, the gases and matrix material enter the reactor from the feed system at the bottom
of the reactor. The fibrous preform undergoes a chemical reaction at high temperature
with the matrix material and thus the latter infiltrates in the fiber or preform crevices.
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5. Types of ceramic matrix composites with process parameters
Fiber Matrix
Common
Precursor
Temperature(℃) Pressure (kpa) Process
Carbon Carbon
Kerosene,
Methane
Approximate
1000
1 Forced flow CVI
Carbon Silicon Carbide CH3SiCl3-H2
Approximate
1000
1 Forced flow CVI
Silicon Carbide Silicon Carbide CH3SiCl3-H2 900-1100 10-100
Isobaric –
Forced flow CVI
Alumina Alumina AlCl3 CO2-H2 900-1100 2-3 CVI
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6. Advantages of CVI process
 Large complex shapes can be produced.
 Residual stresses are lower due to lower infiltration temperature
 corrosion resistance and thermal shock resistance
 very less damage to fibers and to the geometry of the preform due to low infiltration
temperature and pressures
 Very pure and uniform matrix can be obtained by carefully controlling the purity of
gases
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7. Disadvantages
 The residual porosity is about 10 to 15% which is high
 The production rate is low
 The capital investment, production and processing costs are high
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8. Applications
CVI is used to build a variety of high-performance components
 Heat shield systems for space vehicles.
 High temperature systems like combustion chambers, turbine blades, stator vanes, and
disc brakes which experience extreme thermal shock.
 In the case of burners, high temperature valves and gas ducts, oxides of CMCs are used.
Components of slide bearings for providing corrosion resistance and wear resistance.
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