144 Prakt. Met. Sonderband 38 (2006) 
TS1 H. 
The SEM/EDX measurements for the 200h and 400h exposed samples are very similar to the Th 
600h exposed sample. Only the oxide layer thickness changes with exposure time and these hig 
values can be found in Table 2. Figure 2 shows the results of the cross section SEM, WDX an 
and nano indentation results for the 600h exposed sample. A scale of multiple oxide layers is res 
formed. In the SEM image the outer layer appears more dense and homogeneous than the na 
inner layer. The WDX line scan across the oxide scale (Fig. 2b) shows the composition of the sh 
layer structure. Four areas of different compositions across the oxide scale are identified as lay 
the bulk, diffusion zone, inner oxide layer and outer oxide layer. The outer oxide layer has the ch 
highest oxygen and chromium concentrations. The inner layer is iron rich and has less the 
chromium and oxygen than the outer layer. Between these two zones slight silicon ind 
enrichment is found. The diffusion zone shows the transition to the bulk composition. Until ch 
now the exact phases in these oxide layers have not been identified but synchrotron radiation 
measurements are in progress to reveal these structures. Nano indentation is done on this 
material in cross section as well. It is found that the oxide layer has a much lower hardness 
and E-modulus than the steel itself (see Figure 2c). 
°C) 250 r 
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100 ly i 
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ur 30 [Ear Steel i 
| BE te E-moaulus  raraness | 
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Bu Aum m Silicon —%— Chromium —e— Bismutf 
120000 id — 
nh xide Idyers.»=={trangition bulk —¢— Oxygen —#—lron Lead 
8 s0000 - . . 
c Figure 2. (a) The SEM image and 
(350000 (b) the corresponding WDX line 
40000 scan of the T91 material after 600h 
a, oo N exposure in LBE. The nano indents El 
br. [ are visible in the SEM image. (c) 
Bist re , Hardness and E-modulus E 
Depth [um] th 
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