Recent Developments in the Characterization of Extreme-Anisotropic Void Populations in Advanced Thermal Coatings

TA Dobbins1, AJ Allen1, J Ilavsky1,2,D Hass3, H Wadley3 , A Kulkarni4 , J Almer5, F DeCarlo5

1. Ceramics Division, Materials Science and Engineering Laboratory, NIST, Gaithersburg, MD 20899 2. Dept. of Chemical Engineering, Purdue University, West Lafayette, IN 47907 

3. Intelligent Processing of Materials Laboratory, University of Virginia, Charlottesville, VA 229044. NSF Center for Thermal Spray Research, SUNY Stony Brook, Stony Brook, NY 11794-2275

5. Argonne National Laboratory, Advanced Photon Source - XOR

105

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nsity

[cm

-1]

10-4

2 3 4 5 6 7 8 9

10-3

2 3 4 5 6 7 8 9

10-2

2

Q vector [A-1

]

45 degrees 120 degrees 90 degrees Model Intensity

AcknowledgmentsThe UNICAT facility at the Advanced Photon Source (APS) is supported by the University of Illinois at Urbana-Champaign, Materials

Research Laboratory (U.S. Department of Energy (DoE), the State of Illinois IBHE-HECA, and the National Science Foundation), the Oak Ridge National Laboratory (U.S. DoE), the National Institute of Standards and Technology (U.S. Department of Commerce) and UOP LLC.

The SRI-CAT facility at the APS is supported by Argonne National Laboratory. The authors would like to thank Dr. Francesco DeCarlo for his kind assistance in use of the facility.

Use of APS is supported by the U.S. DoE, Basic Energy Sciences, Office of Science, under Contract No. W-31-109-ENG-38.

The NIST Center for Neutron Research is supported by the National Science Foundation and the U.S. Department of Commerce.

Other support from Drexel University’s Center for Plasma Processing of Materials, the National Research Council and the Office of Naval Research is graciously acknowledged.

The authors wish to thank Mr. A. Kulkarni, graduate researcher at SUNY Stonybrook, for useful discussions.

4/30/03

Void microstructures in industrial thermal barrier coatings dictate properties and performance. These physical vapor deposited coatings are formed with micrometer-scale voids between PVD columns and nm-scale voids within PVD columns. Third generation x-ray synchrotron microstructure characterization methods are being used to yield state-of-the-art measurements at high spatial resolutions to provide quantitative parameters about column growth texture and void sizes, size distribution, orientation distribution, and connectivity. These parameters may be used as input for future microstructure-based predictive models or for process control.

Motivation

Characterized by HESAXS and WAXD using 5 m by 50 m beam size, electron beam directed vapor deposited (EB-DVD) coatings show transformation from equiaxed growth (continuous rings) to textured growth (uneven rings). Small angle scattering shows ‘off-axis’ voids more prominent farther from substrate.

SummaryVoid microstructures in physical vapor deposited coatings have been characterized using 2-D collimated Bonse-Hart USAXS, High energy (80keV) small-angle x-ray scattering and x-ray computed microtomography (XMT), resulting in parameters which can be used for studies of microstructure growth and in-service changes.

References1. J. Ilavsky, A.J. Allen, G.G. Long, P.R. Jemian, Review of Scientific Instruments 73[3] 1660 (2002).

2. Dobbins T.A., Allen A.J., Ilavsky J., Kulkarni A., Herman H., “Current Developments in the Characterization of the Anisotropic Void Populations in Thermal Barrier Coatings Using Small Angle X-ray Scattering”, Ceramic Engineering and Science Proceedings 24[3/4], 2003.

Figure 1. Schematic illustrates void microstructures in PVD coatings. m-scale voids between PVD

columns impart strain tolerance. Nm-scale voids within PVD columns lower thermal conductivity.

Off-Axis (~55o ) nm-scale

globular voids.

Crystallographic Texture in EB-DVD Coating

Distances reported are substrate-to-region of interest.

40m 80m 180m

20 m

5 m

SEM Images ofEB-DVD coating.

200m59m

(111)

(200)

(202)(131)

(222)

(400) (111)

(200)

(202)(131)

(222)

(400)(111)

(200)

(202)(131)

(222)

(400)

Systems which exhibit anisotropic growth patterns with preferential orientations, as in PVD coatings, were not possible to analysis using existing small-angle scattering analysis routines. Recently, a scattering model which fits scattering from a system of idealized anisotropic objects to the measured scattering data has been used to quantify scattering from such features. Fitting the 2-D collimated USAXS I vs. Q data to appropriate anisotropic models has been performed at NIST2. Void size and orientation distributions from are reported in Table 1. Results represent statistical scattering data from ~0.008mm3 sample volume. Similar anisotropic models can be applied to HESAXS data.

Small Angle X-ray Scattering from Anisotropic Voids.

p

1pII

ppp d

dNI

incoherent22

pp

BQSQFVdd

sind

)X,Q(d),(Pdd

dd 2

0

2/

0p

)(P)(P),(P P() and P() are orientation distributions.

2

)2/3(o

o2/322

)]X,(KQR[

)X,(KQRJ2

9V

d)X,Q(d

)2/1(22 X)1(1)X,(K where

Mathematical formulation which describes I vs. Q for idealized anisotropic scatterers having

preferential orientation distributions.

Characterization by 2-D Collimated USAXS1, shows finer void sizes after thermal cycling of electron beam physical vapor deposited (EB-PVD) coatings

X-ray Operations and Research

As-Deposited

 

 

As-Deposited EB-PVD Coating

Void Populations

-Orientation Aspect Ratio Mean <O.D.> (nm)

Volume (%)

1: Intercolumnar 85o 0.2 733.82 ± 70 9.0±0.9

2: Coarse Intracolumnar

55o 0.1 173.83±20 2.8 ± 0.3

3: Fine (nm) Intracolumnar

65o 0.05 22.00±2 4.9 ± 0.5

4: Globular 58o 0.7 150±20 4.7± 0.4

Thermally Cycled EB-PVD Coating (10 Cycles comprised of 30 min. heat and 15 min. cool)

Void Populations

-Orientation Aspect Ratio Mean <O.D.> (nm)

Volume (%)

1: Intercolumnar 85o 0.15 551.02 ± 55 9.59± 1.0

2: Coarse Intracolumnar

55o 0.07 141.56±14 6.98 ± 0.7

3: Fine (nm) Intracolumnar

65o 0.05 38.47±4 2.38 ± 0.3

4: Globular 58o 0.1 140±20 6.0± 0.06

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---Data---Model

Anisotropic USAXS from orthogonal slices (Y,Z) in as-deposited EBPVD coating shows model fits to data in

several directions and azimuthal orientations.

Y

Z

Q=0.00026 A-1 Q=0.00101 A-1

X-ray Computed Microtomograph (XMT), reveals the 3-D intercolumnar void microstructure. Efforts are underway to quantify these images via image analysis.

High magnification imageshowing 3-D void interconnectivity.