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Remanufacturing and Advanced Machining
address this issue, platinum-modified nickel aluminide coatings can be produced in two forms, namely a two-phase PtAl2-(Ni-Pt-Al) or a single-phase
Pt-modified β-NiAl. Platinum supports stability of an aluminide coating in
several ways, providing an aluminum-rich surface phase able to form a continuous alumina oxide shell and improve adhesion of the oxide shell formed
on the surface of the coating despite thickening and increasing residual
stresses. Moreover, being a refractory metal, platinum strengthens the outer
layer and increases its hot corrosion resistance.
2. Overlay coatings are fabricated using a pre-alloyed material, such as powder, so that chemical composition of a starting material determines the final
composition of coatings, unlike diffusional coatings, where composition
depends on chemical composition of a substrate. The major advantages of
these coatings include flexibility in choice of coating composition, increased
resistance to high-temperature corrosion and oxidation in comparison with
diffusional coatings, variety of coating thickness, and high ductility compared with other, especially diffusional, coatings. A typical example of an
overlay coating is MCrAlY with a two-phase β+γ microstructure, where the
presence of γ phase increases ductility of the coating and improves thermal
fatigue resistance. ‘M’ stands for a combination of both Ni and Co, and Al
content is typically around 10–12 wt%. Moreover, 1 wt% of yttrium (Y) is
usually added to enhance adherence of the oxide layer.
3. Thermal barrier coatings (TBCs) are widely used for critical high temperature conditions that take place in combustion chambers or rotating blades.
Thermal barrier-coated components must withstand the most extreme temperature, temperature cycling, and high stress. They are expected to withstand thousands of takeoffs and landings in commercial jet engines and
up to 30,000 h of operation in industrial gas turbine engines. TBCs exhibit
important advantages, namely increasing lifetime of parts, improving
engine efficiency since it allows for increasing turbine inlet temperature,
and decreasing coolant air flow. These are achieved through combination
of the multi-material nature of the TBC structure, which in addition to the
demanding operating conditions makes TBCs more complex than any other
coating system. Typically, a TBC coating system consists of four layers
totally different from each other, namely:
1. Super alloy substrate
2. Aluminum intermediate bond coating
3. TGO (thermally grown oxide)
4. Ceramic final outer coating
The term “nano-coatings” sometimes refers to TBCs that are kinds of thin layers
which are in nano dimensions or have substrates in which nanoscale particles have
been dispersed and produce special properties. In many cases, their properties show
significant improvements, in particular, have a higher coefficient of thermal expansion, hardness, and toughness as well as higher resistance to corrosion, abrasion, and
erosion in comparison to micrometer-scale coating structures.
Remanufacturing and Advanced Machining
address this issue, platinum-modified nickel aluminide coatings can be produced in two forms, namely a two-phase PtAl2-(Ni-Pt-Al) or a single-phase
Pt-modified β-NiAl. Platinum supports stability of an aluminide coating in
several ways, providing an aluminum-rich surface phase able to form a continuous alumina oxide shell and improve adhesion of the oxide shell formed
on the surface of the coating despite thickening and increasing residual
stresses. Moreover, being a refractory metal, platinum strengthens the outer
layer and increases its hot corrosion resistance.
2. Overlay coatings are fabricated using a pre-alloyed material, such as powder, so that chemical composition of a starting material determines the final
composition of coatings, unlike diffusional coatings, where composition
depends on chemical composition of a substrate. The major advantages of
these coatings include flexibility in choice of coating composition, increased
resistance to high-temperature corrosion and oxidation in comparison with
diffusional coatings, variety of coating thickness, and high ductility compared with other, especially diffusional, coatings. A typical example of an
overlay coating is MCrAlY with a two-phase β+γ microstructure, where the
presence of γ phase increases ductility of the coating and improves thermal
fatigue resistance. ‘M’ stands for a combination of both Ni and Co, and Al
content is typically around 10–12 wt%. Moreover, 1 wt% of yttrium (Y) is
usually added to enhance adherence of the oxide layer.
3. Thermal barrier coatings (TBCs) are widely used for critical high temperature conditions that take place in combustion chambers or rotating blades.
Thermal barrier-coated components must withstand the most extreme temperature, temperature cycling, and high stress. They are expected to withstand thousands of takeoffs and landings in commercial jet engines and
up to 30,000 h of operation in industrial gas turbine engines. TBCs exhibit
important advantages, namely increasing lifetime of parts, improving
engine efficiency since it allows for increasing turbine inlet temperature,
and decreasing coolant air flow. These are achieved through combination
of the multi-material nature of the TBC structure, which in addition to the
demanding operating conditions makes TBCs more complex than any other
coating system. Typically, a TBC coating system consists of four layers
totally different from each other, namely:
1. Super alloy substrate
2. Aluminum intermediate bond coating
3. TGO (thermally grown oxide)
4. Ceramic final outer coating
The term “nano-coatings” sometimes refers to TBCs that are kinds of thin layers
which are in nano dimensions or have substrates in which nanoscale particles have
been dispersed and produce special properties. In many cases, their properties show
significant improvements, in particular, have a higher coefficient of thermal expansion, hardness, and toughness as well as higher resistance to corrosion, abrasion, and
erosion in comparison to micrometer-scale coating structures.