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Remanufacturing and Advanced Machining
cause softening and ablation and lead to deformation of geometry of components affecting flight performance.
3. The material must have minimum catalytic activity in exothermic reactions
of surface recombination in order to minimize the chemical component of
aerodynamic heating.
4. It must exhibit a high emissivity coefficient and high thermal conductivity,
which provides transfer of energy inside the system, and, as a result, from
the system to the outside environment.
Morks et al. (2013) describe an ultra-high-temperature ceramic (UHTC) as a potential candidate material for advanced aerospace vehicles. Thermal protection systems
in rocket exhaust cones, insulating tiles for space shuttles, engine components, and
ceramic coatings embedded into windshield glass of many airplanes consist of multilayer ceramic coatings that incorporate mullite, yttria stabilized zirconia (YSZ),
and ultra-high-temperature zirconium diboride (ZrB 2 ). In advanced aircraft, it is customary to represent the speed of aircrafts in supersonic terms, exceeding the speed
of sound (Mach 1), and hypersonic terms, five times and above the speed of sound.
In the conditions of supersonic speed, jet engine components are compressed and
thrust by a huge amount of hot gases at above 2500°C. Increasingly severe operating
environment for high-temperature structure materials requires more reliable TBCs
to improve performance of structural materials and extend the operating time and
temperature in these extremely harsh conditions.
According to Morks et al. (2013), the mullite layer in TBC reaches its melting
point within a short time at a high operating temperature (>2500°C). The molten
mullite may seal the stressed ZrB 2 layer penetrating into cracks and pores of ZrB 2 ,
which sheds some light on what could happen at extreme temperatures. Namely,
the mullite layer between ZrB 2 and YSZ layers is to repair the ZrB2 layer that suffers from thermal stresses providing ultra-high-temperature protection. In fact, the
self-sealing for the cracks in ZrB2 layer with molten mullite is the most important
feature of this UHTC multilayer material (Morks et al., 2013). What is more, selfhealing and self-repair is one of the most important directions in development of
components.
Fahrenholtz and Hilmas (2017) note that the family of UHTC materials being
studied at present essentially consists of the same materials that were examined during the space race of the 1950s and 1960s. In their view, discovery of new materials
is needed to expand the number of UHTCs and to extend the number of their potential applications. They believe that the likelihood that a large number of new UHTC
compounds remain undiscovered is extremely low, which may indicate a direction
for development of advanced structural UHTC materials.
2.4 THERMAL SPRAY COATINGS
In order to restore dimensions of worn or corroded components, thermal spray (TS)
coatings are used in every manufacturing industry. Dorfman (2018) underlines that
Remanufacturing and Advanced Machining
cause softening and ablation and lead to deformation of geometry of components affecting flight performance.
3. The material must have minimum catalytic activity in exothermic reactions
of surface recombination in order to minimize the chemical component of
aerodynamic heating.
4. It must exhibit a high emissivity coefficient and high thermal conductivity,
which provides transfer of energy inside the system, and, as a result, from
the system to the outside environment.
Morks et al. (2013) describe an ultra-high-temperature ceramic (UHTC) as a potential candidate material for advanced aerospace vehicles. Thermal protection systems
in rocket exhaust cones, insulating tiles for space shuttles, engine components, and
ceramic coatings embedded into windshield glass of many airplanes consist of multilayer ceramic coatings that incorporate mullite, yttria stabilized zirconia (YSZ),
and ultra-high-temperature zirconium diboride (ZrB 2 ). In advanced aircraft, it is customary to represent the speed of aircrafts in supersonic terms, exceeding the speed
of sound (Mach 1), and hypersonic terms, five times and above the speed of sound.
In the conditions of supersonic speed, jet engine components are compressed and
thrust by a huge amount of hot gases at above 2500°C. Increasingly severe operating
environment for high-temperature structure materials requires more reliable TBCs
to improve performance of structural materials and extend the operating time and
temperature in these extremely harsh conditions.
According to Morks et al. (2013), the mullite layer in TBC reaches its melting
point within a short time at a high operating temperature (>2500°C). The molten
mullite may seal the stressed ZrB 2 layer penetrating into cracks and pores of ZrB 2 ,
which sheds some light on what could happen at extreme temperatures. Namely,
the mullite layer between ZrB 2 and YSZ layers is to repair the ZrB2 layer that suffers from thermal stresses providing ultra-high-temperature protection. In fact, the
self-sealing for the cracks in ZrB2 layer with molten mullite is the most important
feature of this UHTC multilayer material (Morks et al., 2013). What is more, selfhealing and self-repair is one of the most important directions in development of
components.
Fahrenholtz and Hilmas (2017) note that the family of UHTC materials being
studied at present essentially consists of the same materials that were examined during the space race of the 1950s and 1960s. In their view, discovery of new materials
is needed to expand the number of UHTCs and to extend the number of their potential applications. They believe that the likelihood that a large number of new UHTC
compounds remain undiscovered is extremely low, which may indicate a direction
for development of advanced structural UHTC materials.
2.4 THERMAL SPRAY COATINGS
In order to restore dimensions of worn or corroded components, thermal spray (TS)
coatings are used in every manufacturing industry. Dorfman (2018) underlines that