Figure 6 show a cross-section of a sample oxidised at 1000°C for 1hour. Charau 
Results of the FIB examinations show that the thickness tends to grow according to the parabolic atten 
law. 
In Fig.6, another layer is observed under the ALO; layer. This layer seems to be the Ru rich-layer 
that was previously detected. ee 
The zone corresponding to the Ru-rich-layer is composed of sponge-like Al,O3. There was not po 
enough Al to form a compact Al,Oj3 layer. Der 
Because of the absence of a protective layer, the entire Ru was oxidised and evaporated (no Ru was 
found in the EDS Analysis). 
It is probable that the major part of the Ru oxides come from this Ru-rich phase. Abstra 
By uss 
IV. Conclusion microstt 
Isothermal oxidation of the intermetallic compound RuAl was investigated over a temperature range metastal 
of 800-1300°C and studied by TGA, XRD, SEM, EDS and FIB. The following conclusions can be Jocal ct 
drawn: growih 
a) Although the a- Al‚O3 scale exhibited a growth that tends to be parabolic, the TGA analysis crack In 
showed a weight loss due to the volatilisation of Ru-oxides, the major part of which probably the crack 
proceeds from the oxidation of the Ru-rich phase. 
b) The Ru-rich phase formed a porous sponge-like layer which did not have protective properties 
against further oxidation because there was not enough Al to form a compact and protective [ntrodt 
Al,Oj3 scale. Understz 
~ There was no formation of any metastable Al,O; phase. The ALO; phase was formed ars 2. 
directly at ~ 800°C in the heating stage. The sample exhibited an Al-depleted layer under the (1:3). Ti 
Al,Os3 scale. analysis 
d) Above 1200°C the samples had a thick “layer” composed of a succession of Al-depleted and heat-tres 
ALO; layers and also an Al depletion due to the outward diffusion of AI** which was followed contrast 
by the breakdown of the ALO; scale and an inward diffusion of o*. mii 
Acknowledgments 
The authors greatly acknowledge the help of B. Heiland for the Focus Ion Beam Microscopy Exper 
examination, R. Karos for the interpretation of the XRD measurements, J. Schmauch for the help in The me 
the TGA measurements and D. Hohnerlein and J.I. Läzaro for the help in the sample preparation. we 
They also appreciate many helpful discussion with K. Liu. of high 
The research of Professor Frank Mücklich was supported by the Alfried Krup Prize for Young micros 
University Teachers of the Krupp Foundation. soley 
A sing 
beat xz 
References Prior t 
(1) R.L. Fleischer: “Intermetallic Compounds for High-Temperature Structural Use”, Platinum polishe 
Metals Rev. (1992), 36, (3), 138-145. EBSD 
(2) LM. Wolff, G. Sauthoff, L.A. Cornish, H. DeV. Steyn and R. Coetzee: “Structure-property ' 
application relationships in Ruthenium aluminide RuAl”, Structural Intermetallics (1997), 815- he 
823. under s 
(3) A. Olivei: “Methods for studying oxygen-platinum metals interactions”, J. Less-Common RE, 
Metals, (1972), 29, 11-23. = 
[RY 
158