M. GORAL 723
slurry consisting of multicomponent MeCrAlY alloy.
However, one has met some difficulties resulting from a
high density of introduced MeCrAlY powder. One has
observed the sedimentation of heavier powder compo-
nents on the bottom of the vessel during the application
process. All obtained coatings were characterized by a
structure, which is typical for highly active process and
was created during the inward diffusion of aluminium.
After the diffusion heat treatment process one has also
observed a presence of many fractures in the coating re-
sulting from internal stresses. It could be caused by a
short time of diffusion annealing process (2 h), fast cool-
ing and using of hydrogen atmosphere, instead of argon
atmosphere used till now. It caused in the coatings with
the addition of NiCoCrAlY powder fractures and exfo-
liation of the outer layer with high content of silicon and
chromium. In the structure of all obtained aluminide
coatings, a few characteristic zones can be observed. In
the layer obtained form a commercial slurry containing
only aluminum and silicon powders, the outer zone was
rich in silicon and chromium, which could be a proof of
silicide formation. In all layers, one observed the zone
with fine porous precipitates with the diameter less than
1 μm. They contained silicon on the basis of the β-NiAl
intermetallic phase, with 50 at% of aluminum. In all lay-
ers, the inner zone with a thickness of approx. 5 μm was
observed. The result of cyclic oxidation tests showed an
increase of oxidation resistance of samples with alu-
minide layers. The research did not proved a significant
difference in oxidation resistance between layer made
from commercial Al-Si slurry and layer modified with
MeCrAlY powder. It was caused by the observed sedi-
mentation process of the powder. One observed no in-
fluence of the additional outer layer with high silicon and
chromium content, on the increase of oxidation resis-
tance of the layer created from the commercial Al-Si
slurry. The presented results indicate the significant dif-
ficulties in obtaining the aluminide coatings modified by
powders, which are made of metals being components of
MeCrAlY alloy and have higher density. It is necessary
to prepare a new binder, which ensures the possibility of
homogenization of the slurry and prevents the sedimen-
tation process. Searching for new methods of obtaining
thermal barrier coatings is a significant reason for con-
tinuing the research. The European Project “Particoat” is
a good example of it.
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