PERFORMANCE EVALUATION AND MODELING OF EROSION RESISTANT TURBINE ENGINE THERMAL BARRIER COATINGS

Dr. Robert A. Miller, Dr. Dongming Zhu, and Dr. Maria Kuczmarski

NASA Glenn Research Center Cleveland, Ohio 44135

Abstract The erosion resistant turbine thermal barrier coating system is critical to the rotorcraft engine performance and durability. The objective of this work was to determine erosion resistance of advanced thermal barrier coating systems under simulated engine erosion and thermal gradient environments, thus validating a new thermal barrier coating turbine blade technology for future rotorcraft applications. A high velocity burner rig based erosion test approach was established and a new series of rare earth oxide- and TiO2/Ta2O5-alloyed, ZrO2-based low conductivity thermal barrier coatings were designed and processed. The low conductivity thermal barrier coating systems demonstrated significant improvements in the erosion resistance. A comprehensive model based on accumulated strain damage low cycle fatigue is formulated for blade erosion life prediction. The work is currently aiming at the simulated engine erosion testing of advanced thermal barrier coated turbine blades to establish and validate the coating life prediction models.

https://ntrs.nasa.gov/search.jsp?R=20130013140 2020-06-08T03:17:43+00:00Z

1Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Performance Evaluation and Modeling of Erosion Resistant Turbine Engine Thermal Barrier Coatings

Dr. Robert A. Miller, Dr. Dongming Zhu *, Dr. Maria Kuczmarski

Structures and Materials DivisionNASA Glenn Research Center

Cleveland, Ohio

* Army Research Laboratory at NASA Glenn Research Center; Presenter

NASA Fundamental Aeronautics Program Annual Meeting, Atlanta, Georgia,October 7 - 9, 2008

2Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Motivation

— Innovative turbine coating and component materials are enabling technologies for advanced rotorcraft engine development

— Durable thermal barrier coating (TBC) technology is especially crucial for improving rotorcraft engine performance and reliability

Combustors and shrouds

Turbine vanes and

blades

Component technologies for reduced engine specific fuel consumption, increased power density, and reduced

maintenance cost

Ceramic coating

Ceramic coating

SubstrateSubstrateBond coat

Bond coat

Tgas

Tsurface

Tgas

Tsurface

TbackTback

Ceramic coating

Ceramic coating

SubstrateSubstrateBond coat

Bond coat

Tgas

Tsurface

Tgas

Tsurface

TbackTback

Ceramic coating

Ceramic coating

SubstrateSubstrateBond coat

Bond coat

Tgas

Tsurface

Tgas

Tsurface

TbackTback

(a) Current TBCs (b) Advanced TBCs

Advanced TBCs can significantly increase turbine inlet temperature and

thus efficiency

3Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Erosion Resistant Thermal Barrier Coatings for Improved Turbine Blade Life

• Objective─ Develop erosion resistant turbine blade thermal barrier coatings─ Develop physics-based life model and design tools for predicting blade coating erosion and degradation under simulated engine environments

• Approach─ Establish advanced erosion high-heat-flux test rigs for turbine TBC evaluations─ Develop advanced thermal barrier coatings based on nano-tetragonal t’ phase toughening approaches─ Advanced mechanism- and physics-based modeling

• Benefits─ Facilitate turbine thermal barrier coating design and applications─ Improve erosion resistance and durability─ Increase turbine temperature capability by 300˚F leading to higher fuel efficiency─ Establish advanced modeling methodologies Typical turbine airfoil

thermal barrier coating

25 µm

Ceramic coating

Bond coat

4Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Outline

• High temperature erosion testing development─ High velocity burner erosion rig simulating engine environments─ Computational Fluid Dynamics (CFD) modeling ─ Experimental validation of high temperature erosion testing

• Low conductivity turbine thermal barrier coating developments─ Low conductivity TBC design approach─ High toughness erosion resistant turbine airfoil TBC development─ Calcium-magnesium-alumino-silicate (CMAS) interaction testing

• Coating Performance and Life Prediction─ High toughness turbine erosion coating modeling─ Sintering-creep, oxidation and thermo-mechanical fatigue mechanisms

• Future Plans• Summary

5Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

High Velocity Burner Erosion Rig

─ Burner capable of up to Mach 1 velocity with erodent particulate injection

─ 0.75” to 1” diameter exhaust nozzle─ Temperature up to 2200˚F ─ Thermal gradient erosion testing─ Flexible test configurations

- 1” and 2” diameter disk specimens- Coated turbine blades

Mach 0.3-1.0 burner erosion rigSpecimens in testing

6Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Computational Fluid Dynamics (CFD) Modeling

─ Computational Fluid Dynamics (CFD) modeling predicting burner flow and particle velocities in conjunction with experiment validation

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Mach 0.4, 50 micron particlesMach 0.4, 560 micron particlesMach 0.9, 50 micron particlesMach 0.9, 560 micron particles

Parti

cle

velo

city

, m/s

Distance from injector, m

nozzle exit

specimen location

Gas velocity m/s

Mach 0.9

Mach 0.4

Maximum velocity 754 m/s

Maximum velocity 344 m/s

High speed camera image for particle trajectories

7Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Modeling of Erodent Particle Trajectories and Coating Erosion Test Approach

─ Erosion particulate trajectories modeled to understand high temperature erosion test configuration

─ The test rig demonstrated in coating erosion screening tests

- Examples of eroded 1” diameter disk specimens- Erosion crater profiles similar to those in erosion

standard G76-05 for coating downselect An erosion crater profile after testing

Modeled for 27 micron erodent

8Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Erosion Resistant Low Conductivity Thermal Barrier Coatings

─ Multi-component oxide defect clustering approach (Zhu and Miller, US Patents No. 6,812,176, No.7,001,859, and 7,186,466; US patent application 11/510,574 )

─ Lower thermal conductivity and improved thermal stability

EELS elemental maps of EB-PVD ZrO2-(Y, Gd,Yb)2O3

TEM Moiré fringes of EB-PVD ZrO2-(Y, Nd,Yb)2O3

e.g.: ZrO2-Y2O3-Nd2O3(Gd2O3,Sm2O3)-Yb2O3(Sc2O3) – TiO2-Ta2O5 systemsPrimary stabilizer

Oxide cluster dopants with distinctive ionic sizesToughening dopants

Advanced turbine WDS composition maps

O Yb

Zr

9Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Thermal Conductivity of Advanced Turbine Thermal Barrier Coatings

10Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Impact Resistant Low Conductivity Thermal Barrier Coatings

– Tetragonal t’ phase toughened low conductivity coatings showed improved impact resistance compared to the cubic-phase coatings in impact tests

11Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Erosion Resistance of Low Conductivity Thermal Barrier Coatings

– Tetragonal t’ phase toughened low conductivity coatings showed improved 50 micron size particulate erosion resistance compared to the cubic-phase coatings in erosion tests

12Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Erosion Resistance of Low Conductivity Thermal Barrier Coatings

– Advanced processing showed promise in improving 27 micron particle erosion resistance of low conductivity TBCs

13Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Physics-Based Erosion Model Development

– Physics-based erosion models being developed to predict turbine TBC erosion and degradation behavior

– Multiple physics-base processes and mechanisms considered

- Turbine TBC sintering and creep - Erosion (erosion fatigue mechanism) - Low cycle fatigue- Molten Calcium Magnesium Alumino-Silicate (CMAS) interactions

Variable erosion rates during the erosion process under high-heat-flux and thermal gradient cyclic conditions

14Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Sintering Cracks and Delaminations of Thermal Barrier Coatings

— Baseline ZrO2-7wt%Y2O3 turbine coating tested under laser simulated engine heat flux conditions

— Sintering strain corresponding to the thermal gradient across the coating (Tsurface=1280˚C , Tinterface=1095˚C )

— Coating delamination under high-heat-flux cyclic environments

0.00

0.50

1.00

1.50

2.00

0 50 100 150 200 250

0 hr46 hr200 hrmean strain

Surf

ace

open

ing

stra

in, %

Time, hours

strain (in%) = 0.40757 + 0.41 · t (in hr) 0.2

100 µm

15Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Modeled Sintering-Creep Strains as a Function of Temperature and Time

0.5

0.5

0.5

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1

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1.5

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0 60 120

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720

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840

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1020

1080

1140

1200

1260

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1380

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1500

TBC

surf

ace

tem

pera

ture

, °C

Time, hours

Sintering/creep cyclic fatigue dominant failure

Erosion dominant failure

— Erosion dominant region vs. sintering-creep dominant region— Strong interactions in accelerated damage accumulation

16Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Impact Failure of Advanced Multi-Component Low Conductivity Thermal Barrier Coatings

30 um30 um

Surface sintering and impact densification zone

SEM micrographs of advanced thermal barrier coating after impact/erosion damage

Backscattered electron imageSecondary electron image

― Surface sintering and impact densification zone interaction, with subsequent spallation

17Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Erosion Damage Accumulations

― Multi-level delaminations under combined erosion impact loading and thermal gradients

18Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Erosion Rates

Erosion rate (mg/g erodent) in erosion dominant regime – dynamic impact effect will be incorporated

─ Fatigue strain based models incorporate multiple mechanisms

2/32

32/1

Hv

Kec

erodentTBCTBC

⋅

⋅⋅⋅=

⋅

ερρ

cfoxidationpLCFpfluxheatpcreepperosionp N εεεεεε =⋅∆∆∆∆∆Σ −−−−−2/1

_ ),, ,,(

The erosion model development and validation: Emphasizing more realistic testing condition

and mechanisms interactions

KerodentTBC ρρ ,

cε

H

- Constant

- Densities of coating and erodent, respectively

- Critical strain to failure

- Dynamic hardness

cferosionp N εε =⋅∆ −2/1

19Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Additional Failure Driving Forces

─ Fatigue strain based models incorporate multiple mechanisms─ Elastic modulus and activation energies determined from experiments

( )( )211 1 0

1

116 1 SG E h T Tν α

ν +

= − −

2

2

/ 2[ (1 ) /(1 )]( ) / 2

G h EEh Tσ

ν ν α

=

= + − ∆ ∆

- Thermal expansion mismatch

- High heat-flux effect

- Creep and oxidation

( ) ssvolumep tx

RTQQ

A −⋅⋅

+−⋅= σε exp&

+−⋅= −−

− RTQQ

B oxGBoxVolumeoxp expε&

1 1,E ν

2 2,E ν

hP∆

M∆

interfacedelamination crack

σ

coating

substrate

20Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Laser High Heat Flux Rig for Molten Sand Erosion and CMAS Interactions

─ CMAS effect taken into account for coating development ─ Accelerated failure observed with CMAS interactions─ Modeling emphasis on coating densification and resulting delamination

failure

Specimen under the rig test

(a) Upon initial heating

(b) After testing

Combustor TBC

(c) Baseline coating

Turbine TBCs

(d) Advanced coating50 hrs

Erosion jet

21Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Plans

• Emphasize burner erosion resistance and coating life models

- Optimize high toughness erosion resistant turbine coatings

- Investigate and model erosion, creep, fatigue, and CMAS interactions

- Develop methodologies and key experiments for model validation

- Develop turbine blade TBC erosion-oriented life prediction models and design tools

22Fundamental Aeronautics Program Annual Meeting, October 7-9, 2008 Subsonic Rotary Wing Project

Summary

• High temperature erosion testing capability developed under the Subsonic Rotary Wing project

• CFD models established to understand gas and erodent flows

• Advanced turbine thermal barrier coatings developed for rotorcraft engines with combined low conductivity and high toughness

• Models formulated addressing the erosion, sintering and fatigue interactions – strain damage accumulations

• Physics-based turbine blade coating erosion lifing models and model validation emphasized in the current efforts