Baden, 09.03.2006

Acceptable limits of degradation of TBC forhigh-efficient turbines (HET TBC)

Department Materials (ALSTOM)

Lab of Crystallography (ETH Zürich)

CTI project Nr. 7820.3 EPRP-IW

Project start Nov. 1. 2005

Project duration 24 months

Outline

1 Evolution of coating microstructure with heat treatment

2 Measurements of coating macro-strains

3 SEM pictures of Sulzer Metco coatings

Evolution of coating microstructure with heat treatment

Measurements allow to determine:

1 Monoclinic content

2 Cell parameters of tetragonal YSZ (and Yttrium content)

3 Stresses and grains size

Coating D2426 was treated at 1100ºC for various times and then measured by XRD.

Evolution of monoclinic content with heat treatment

Monoclinic increases after 1h of heat treatment and is stable after 24h of heat treatment

Evolution of Yttrium content with heat treatment

After 1h of heat treatment the Yttrium content seems to increase. Both cell parameters a and c decreases.

After 24h of heat treatment, the Yttrium content decreases, the cell parameter a remains constant and c increases.

Evolution of particle size and strains with heat treatment

γ =X

cosθ+ γ sd

2 tan2θ

γ s = ηΓ sΓ s = S400 (h

4 + k 4 ) + S004l4 + 3(S220h

2k2 + S202 (h2l2 + k2l2 ))

Peak profile is described with a pseudo-Voigt function (mixing of a Gaussian with a Lorentzian function).

The Lorentzian part of the peak profile is described by:

γs is the micro-strains broadening of the peak profile which is described by a tensors having only 4 non zero components (S400, S004, S220, S202)

p =18000Kλ

πX

Evolution of particle size and strains with heat treatment

The particle size can be obtained from the following expression:

Grain size does not change after 24h heat treatment

Evolution of particle size and strains with heat treatment

Heat treatment time (hours)

S400 S004 S220 S202

0 0.78473 0.38320 -0.21543 0.15859

1 0.69468 0.36941 -0.11450 0.11464

24 0.66869 0.33691 -0.11288 0.10068

Micro-strains decrease with heat treatment time as can be seen from the decrease of all Shkl values

Measurements of coating macro-strains

Macro-strains are measured from peak shift for different coating orientations (angle )

S1

S2

S3

ε(%) =dψ − d0d0

=1+ ν

Eσ 11 sin

2 (ψ ) −ν

E(σ 11 + σ 22 )

Since d0 is usually difficult to know one can use the d value for =0 for d0.

Measurements of coating macro-strains

- One observes 0.1% strains in the coating from the peak shift measurement

- A whole pattern fitting was performed and strains where calculated from cell parameters giving much lower values

- This difference can be explained by an shift of the diffraction plane which can lead to error in the peak shift measurement

SEM pictures of Sulzer Metco coatings

Sample was too big to allow EDX measurements (too small working distance)

The polishing was not good enough and we had to polish the sample again

The coating looks homogeneous and only one ‘non-molten’ particle was found (in the right side picture)

SubstrateCoating ‘Non-molten’ particle