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partially united. Fig. 2.
13
c: bias 800 V, 
I
ems = 
100 mA. The grains are united and 
higher. The micrograph in Fig. 2.
13c shows a columnar 
(
dendrite
) 
structure. It is 
known that the significant advantage of the columnar microstructure for high 
temperature application gives better strain tolerance between the coating and the 
substrate. 
Effects of ion beam assisted deposition, beam sharing and pivoting in EB
-
PVD processing of graded thermal barrier coatings was investigated. Processing 
125 

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technology was developed to form graded TBCs by coupling ion beam assisted 
deposition with substrate pivoting in the alumina-
YSZ system. 
Fig. 2.13. SEM image of Cr coating 
on
 Ni
-
based alloys: 
(
a) without bias, 
I
ems = 40 
mA;
 
(
b) bias 800 V, 
I
ems = 60 
mA;
 
(
c) 
bias 800 V, 
I
ems = 100 mA. 
Graded thermal barrier coatings, which 
consist of transition layer, bonding layer, 
barrier for oxidation and corrosion 
functional cover layer de
posited by EB
-
PVD in a one
-step cycle were 
investigated. The chemical affinity 
between the intermediate layers and the 
adjustment of the ceramic top layer to 
the substrate via this multilayer stack as 
a material adapter is proposed and 
experimental realiz
ed. 
Proposed for the multilayer stack 
architecture is:
each layer has a chemical element 
in common with neighbouring layers; 
this chemical affinity ensures the 
chemical compatibility between the 
layers; 
the graded compositional 
transition between the layers ensures 
mechanical compatibility;
the use of accelerated ions for 
activating the growth of the films leads 
to formation of the necessary 
morphology and improved adhesion. 
Here is the proposed architecture of the 
multilayer stack shown (Fig.
2.14
):
L1: 
Ni
-
based substrate;
L2: 
Ni
-based substrate is siliconized for better corrosion resistance and for 
the compatibility to the next layer which contains Si, too;
L3: is a bonding 
AlSi
which will replace conventionally used expensive 
PtAl. The graded composition
provides a good adjustment of thermal expansion 
coefficients; 
L4: serves as an oxidation barrier;
L5: has to lower the thermal conductivity and to optimize the cooling rates.
126

---

Fig. 
2.14. 
The proposed multilayer stack.
In the Ion Assisted EBPVD system, a 6 kW electron beam evaporator is 
used with a 270° beam deflection
 
by 
a permanent magnet and with a 10 kV 
acceleration voltage. To measure the density of the ionic and electronic current, a 
special ion detector was installed in the position of the substra
te. The main process 
data can be listed as follows: vacuum: 10
-5
-5·10
-
6
mbar; emission current of the e
-
gun: 15 mA to 400mA dependent on the evaporated metal and stages of the 
process run; bias potential: O V to 1000 V. As coatings: (Ti
-
Al), Si
-
(Si
-
Al) was 
chosen; as substrates
- nickel-
based alloy 617. The distance between the 
evaporation surface and the substrate was 150 mm. The thicknesses of the 
deposited films were measured by direct SEM examinations of cross
-sections. 
The adjustment of the top layer to the intermediate layer stack is exhibited 
by the deposition of (ZrO
2
+ Al
2
O
3
) and C 
–
ZrO
2
on the (Ni
-Al-
Si) substrate.
(Fig.2.
1
5, Table 2.)
The top layer 1 shows a stoichometric composition of ZrO
2.