Optimized high purity coating for high temperature thermal cycling applications

Abstract

The invention is directed to a blended material and method for obtaining thermal barriers for high temperature cycling applications that have both high sintering resistance to achieve a high service lifetime and low thermal conductivity to achieve high operating temperatures. These materials are additionally suited for use in high temperature abradable (rub seal) coatings. The invention provides desired coating structures so that the changes in the coating microstructure over the in-service lifetime are either limited or beneficial.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority under 35 U.S.C. § 119(e) from U.S. Provisional Patent Application No. 60 / 724,286, filed on Oct. 7, 2005, which is incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] Not Applicable REFERENCE TO A “MICROFICHE APPENDIX”[0003] Not Applicable BACKGROUND OF THE INVENTION [0004] 1. Field of the Invention [0005] The invention relates to ceramic materials for thermal barriers and abradable coating systems in high temperature and high temperature cycling applications, and more particularly to ultra-pure zirconia and / or hafnia materials for use in thermal barrier and abradable coating applications. [0006] 2. Description of the Related Art [0007] Superior high-temperature properties are required to improve the performance of heat resistant and corrosion resistant members. These members include, for example gas turbine blades, combustor cans, ducting and nozzle gui...

AI Technical Summary

Benefits of technology

[0017] In a further aspect of the invention, a method for producing a high-purity coating structure is provided. The method includes providing a first material consisting essentially of about 4 to 20 weight percent of a stabilizer of one or more rare earth oxides, and a balance of at least one of zirconia (ZrO2), hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and / or hafnia (HfO2) is partially stabilized by the stabilizer, and wherein the total amount of impurities is less than or equal to 0.15 weight percent. Another step of the method includes providing a second material of a different composition than the first material, said second material consisting essentially of about 4 to 20 weight percent of a stabilizer of one or more rare earth oxides, and a balance of at least one of zirconia (ZrO2), hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and / or hafnia (HfO2) is partially stabilized by the stabilizer, and wherein the total amount of impurities in second material is less than or equal to 0.15 weight percent. Yet another step of the method includes and applying said materials onto a metal substrate.

[0008] Thermal barrier coatings are used to insulate components, such as those in a gas turbine, operating at elevated temperatures. Thermal barriers allow increased operating temperature of gas turbines by protecting the coated part (or substrate) from direct exposure to the operating environment. An important consideration in the design of a thermal barrier is that the coating be a ceramic material having a crystalline structure containing beneficial cracks and voids, imparting strain tolerance. If there were no cracks in the coating, the thermal barrier would not function, because the differences in thermal expansion between the metal substrate system and the coating will cause interfacial stresses upon thermal cycling that are greater than the bond strength between them. By the creation of a crack network into the coating, a stress relief mechanism is introduced that allows the coating to survive numerous thermal cycles. Repeating crack networks are typically imparted into the coating on varying space scales by manipulating the thermodynamic and kinetic conditions of the manufacturing method, and different structures known to perform the coating task have been optimized likewise. In addition to this, cracks are also formed during service, so the structure formed upon coating manufacture changes with time, depending on the starting material phases in the manufactured coating and thermal conditions during service. There remains a need in the art for a coating material, coating material manufacturing method and coating manufacturing method that address the changes in the coating microstructure during its service lifetime.

[0020] The accompanying drawings are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the figures:

Problems solved by technology

An additional design criteria for gas turbines is increased operating time between maintenance and repairs, meaning longer lifetime of the materials used in these applications.

If there were no cracks in the coating, the thermal barrier would not function, because the differences in thermal expansion between the metal substrate system and the coating will cause interfacial stresses upon thermal cycling that are greater than the bond strength between them.

In addition to this, cracks are also formed during service, so the structure formed upon coating manufacture changes with time, depending on the starting material phases in the manufactured coating and thermal conditions during service.

When the coating is cycled above half of its absolute melting temperature, the coating begins to sinter causing volume shrinkage.

A major disadvantage brought about by using typical zirconia coating systems is that zirconia is transparent to radiation in the infrared range.

As thermal barriers are sought for higher temperatures, zirconia becomes limited in its effectiveness.

Images