Pyrochlore Thermal Barrier Coating Spalling Prevention
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Solution Overview
Problem
Conventional thermal barrier coatings for gas turbines, particularly those using YSZ, suffer from spalling due to insufficient stability under high-temperature conditions and thermal stress, leading to reduced durability and heat resistance.
Innovation Solution
A thermal barrier coating system comprising a ceramic layer with a pyrochlore-type crystal structure, doped with CaO and MgO, and a zirconia-containing layer with vertical cracks, applied on a heat-resistant substrate to reduce thermal conductivity and enhance thermal cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If YSZ ceramic layer is used for thermal barrier coating, then thermal conductivity is reduced and thermal barrier effect is improved, but spalling occurs due to insufficient stability under high-temperature conditions and thermal stress
Solution Approach 1:
The patent changes the crystal structure parameter of the ceramic layer from conventional YSZ (cubic or monoclinic) to pyrochlore-type structure by controlling sintering temperature and composition. This parameter change results in a ceramic layer with simultaneously reduced thermal conductivity and improved thermal stability, preventing spalling under high-temperature conditions while maintaining thermal barrier effectiveness
Solution Approach 2:
The patent creates a composite thermal barrier coating system combining the bond coat layer with the pyrochlore-type ceramic layer. This composite structure integrates the adhesion benefits of the bond coat with the superior thermal properties of the pyrochlore ceramic, achieving both strong bonding and resistance to spalling under thermal cycling conditions
2Reliability
If YSZ ceramic layer is used for thermal barrier coating, then thermal barrier performance is achieved, but spalling occurs due to difference in coefficient of thermal expansion from substrate and bond coat layer
Solution Approach 1:
The patent modifies the thermal expansion parameter by adopting the pyrochlore crystal structure, which inherently provides better thermal expansion compatibility with the bond coat and substrate. This reduces the thermal stress generated during thermal cycling and prevents spalling while maintaining the thermal barrier function
Solution Approach 2:
The patent introduces a porous structure within the pyrochlore-type ceramic layer, creating voids that can accommodate thermal expansion differences between layers. This porous architecture reduces overall thermal stress and prevents spalling while the pyrochlore structure maintains low thermal conductivity for effective thermal barrier performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed coating system effectively suppresses spalling and maintains high thermal barrier performance even at elevated temperatures, improving the reliability and longevity of gas turbine components.
Implementation Method 1
a ceramic layer having a pyrochlore-type crystal structure... to reduce thermal conductivity and enhance thermal cycle durability
Implementation Method 2
a thermal barrier coating (TBC), a laminate of ceramic layers composed of oxide ceramics, is formed on the refractory-metal substrate... so as to protect from high temperatures
Data Source
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AI summary
There are provided a thermal barrier coating material and a thermal barrier coating member that can suppress spalling when used at a high temperature and have a high thermal barrier effect, a method for producing the same, a turbine member coated with a thermal barrier coating, and a gas turbine. The thermal barrier coating member comprises a heat resistant substrate 21, a bond coat layer 22 formed thereon, and a ceramic layer 24 formed further thereon, wherein the ceramic layer 24 comprises an oxide which consists of an oxide represented by the general formula A2Zr2O7 doped with a predetermined amount of CaO or MgO and has 10 volume % or more of a pyrochlore type crystal structure, where A represents any of La, Nd, Sm, Gd, and Dy.