The document discusses silicon carbide (SiC) ceramics, including their unique properties, microstructure, densification challenges, and common uses. It describes how sintering aids can be used to achieve high density at lower temperatures and pressures. Liquid phase sintered SiC ceramics are favored for tribological and structural applications due to properties like high hardness, strength, and thermal conductivity. The document summarizes typical applications of SiC ceramics in abrasives, automotive components, electronics, armor, and more.

1. TRIBOLOGICAL STUDY
OF SiC
118CR0123 COU RSE MENTOR
THANSEER JARSHAN A PROF.DEBASISH SARKAR
DEPARTMENT OF CERAMIC ENGINEERING

2. INTRODUCTION:
 Silicon carbide structural ceramic is widely used in industries because of its
unique combination of properties such as:
◦ High hardness
◦ High modulus
◦ High temperature strength
◦ Good oxidation resistance
◦ Good thermal shock resistance
◦ High thermal conductivity

3. A coordinated tetrahedron, either SiC4 or CSi4, is the
primary structure of covalently connected silicon carbide.
Although there are many other SiC polytypes, the cubic
polytype (β-SiC) and non-cubic structures (hexagonal or
rombohedral) as α–SiC are the most common.
Densification of SiC powders at lower temperatures is
challenging due to the strong covalent link and extremely
low self-diffusion coefficient (10^-13—10^-14 cm2 / sec).
Only at extremely high pressures (30-100 MPa) and
temperatures above 2100 C is densification conceivable.
Sintering aids are required in order to obtain high density
at lower temperatures and pressures.

4. Sintering additives such as metal oxides, Al-B-C, and
AlN–metal oxides alter the microstructure of SiC
ceramics and increase fracture toughness during
liquid-phase sintering.
Because of the combination of intergranular crack
mode induced by the glassy grain boundary phase
and energy dissipation mechanisms in the crack
wake, platelet-reinforced microstructures have
increased toughness.
The crystallinity of the grain boundary phase of SiC
ceramics is also affected by the sintering additive
composition.

5. Liquid phase sintered silicon carbide (LPS-SiC) ceramics are
favoured for a variety of tribological and structural
applications due to their appealing features such as:
 In turbine parts
 Heat exchanger tubes
 Bearings
 Mechanical seals
 Cylinder liners
 Burner parts in fluidized bed combustion system
 Cutting tools

6. The coefficient of friction (COF) in unlubricated sliding
studies stated to be varied in the wide range of 0.2 - 0.8,
which dropped to 0.02 in lubricating media such as water,
paraffin oil, and so on, based on the circumstances of sliding
and features of SiC and SiC composites.
The wear rates under sliding situations ranged from 10^-7
to 10^-4 mm3 / N.m.
The erosion of SiC ceramics is mostly researched under
solid particle erosion circumstances, with little research done
under cavitation conditions.

7.  Solid particle erosion of SiC and SiC-based composites is
typically caused by brittle fracture as a result of lateral and
radial cracking, according to reports.
 Based on erosion parameters, microstructural and
mechanical features of SiC ceramics, the erosion rate varies
from 10^-1 to 10^3 mm3 /kg.
Several material removal mechanisms, such as mechanical
fracture, chipping, plastic deformation, ploughing, and
or formation and removal of tribooxide layer, were mostly
responsible for the complex tribological behaviour of SiC
ceramics and their composites in sliding and solid particle
erosion conditions.

8. APPLICATIONS:
At higher temperatures, silicon carbide generates natural
crystals that are harder, more abrasive, and dissociate or
sublimate. Silicon carbide is employed in the following
applications as a result of this:
Abrasive Industry:
Because silicon carbide has a high hardness, it is the best
option among raw materials for abrasive pipe, pumping
chambers, and other applications. Silicon carbide has
abrasive properties that are 5 to 20 times greater than cast
iron and rubber.

9. Automobiles:
Because of its ability to endure severe temperatures, silicon
infiltrated carbon-carbon composite is utilised for high-
performance ceramic brake discs.
Carbon fibre reinforced silicon carbide (C/SiC) is produced
when silicon interacts with graphite in a carbon-carbon
composite.
Some road-going sports cars, supercars, and other
performance automobiles employ these discs, such as the
Porsche Carrera GT, Bugatti Veyron, Bentleys, Ferraris,
Lamborghinis, and some specialised high-performance Audis.

10. ELECTRONICS:
In research and early mass manufacturing, silicon carbide is
employed as a semi conductor, giving benefits for rapid, high
temperature, and/or high voltage devices.
Schottky diodes were the first devices accessible, followed
by junction gate FETs and MOSFETs for high-powered
switching.
Bipolar transistors are being developed right now.
It's also employed in the production of LEDs.

11. STRUCTURAL MATERIALS:
Silicon carbide is used in composite armour and ceramic
plates in bulletproof vests, along with other strong ceramics.
Silicon carbide is utilised as a support and shelf material in
high-temperature kilns, such as those used for burning
ceramics, glass fusing, or glass casting.
SiC kiln shelves are far more durable and long-lasting than
alumina shelves.

12. TYPICAL SILICON CARBIDE USES:
Covers for suction boxes.
Turbine components that are both fixed and movable.
Bearings and seals.
Parts for ball valves.
Gas flow liners that are hot.
Heat exchangers are devices that transfer heat from one
place to another.
Equipment for semi-conducting processes.
Jewellery.

13. Summary and future scope:
Wear and friction characteristics of SiC ceramics change
with microstructural modification while sliding.
Wear resistance was improved by a hard interlocking
network of elongated grains or grains with a high aspect
ratio.
Clear grain boundaries in SiC ceramics outperformed
amorphous grain boundaries in terms of wear resistance.
When SiC ceramics have a coarse grain structure, the
transition from moderate to severe wear happens more
quickly than when the grain structure is fine.
Doping elements alter the kinetics of tribochemical
reactions, resulting in various friction and wear
characteristics.

14. Summary and future scope:
The majority of research used ambient temperature
mechanical and microstructural properties of SiC ceramics to
predict high temperature wear behaviour, however the
influence of microstructural and mechanical features at
selected temperatures should be addressed when assessing
actual potential.
Future research into the influence of microstructural or
mechanical properties at low temperatures will look into the
possibility of SiC ceramics and composites for usage in space
or maritime applications.

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