Metallographic Characterisation of the Oxidation Protective Layer in RuAl 
hn baw, py Based Intermetallics 
It Glasperlen 
Sen die mit den N.Manent Conesa?), N.Ilic®, H.Natter® F. Soldera®, F Miicklich® 
4 scharfkantioe (1) Functional Materials, Dep. Materials Science, Saarland University, Saarbrücken, Germany 
’ (2) Physical Chemistry, Saarland University, Saarbriicken, Germany 
0S und die 
2 Prof und Abstract | . . . 
gen die gleiche [sothermal oxidation of the intermetallic compound RuAl was investigated over a temperature range 
IE eine Oft den of 800-1300°C. Although the «-AlLO; scale exhibits a growth that tends to be parabolic, the 
Stalin thermogravimetric analysis show a weight loss due to the volatilisation of Ru oxides. The major 
part of the Ru oxides probably does not arise from the oxidation of the intermetallic phase but from 
the oxidation of the Ru-rich phase. This phase formed a porous sponge-like layer which did not 
se have protective properties against further oxidation as there was not enough Al to build a compact 
and protective Al,Oj3 scale. 
There was no formation of any metastable Al,O; phase. The a-Al,O; phase was formed directly at 
~ 800°C in the heating stage. The samples exhibited an Al-depleted layer under the Al,O; scale. 
Above 1200°C the samples developed a thick zone composed of a sequence of Al-depleted and 
AL Os layers. The Al-depletion, caused by APP" outward diffusion, is followed by the breakdown of 
the Al;O; layer .This allowed the O?% inward diffusion and successive oxidation. 
I. Introduction 
From the large number of intermetallic compounds identified so far, a relatively small number can 
be used in high-temperature applications and only several of them show good toughness at ambient 
temperature [1]. One example is the RuAl intermetallic compound, which differs from the other 
high-temperature intermetallics because it possesses an unusual combination of ductility, 
Wir thermodynamic stability, and corrosion resistance. 
The resistance against oxidation in aluminium based intermetallics depends on the formation of a 
delisubstanz. protective a-Al,O3 scale which suppresses inward penetration of oxygen. The aim of the present 
stimmen. die study is a better understanding of the oxidation mechanisms of the intermetallic compound RuAl by 
mittelt wurden, the determination of the oxidation kinetics and of the different transformation of the Al,‚O3 scale. 
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II. Experimental 
t eine Que Samples with a nominal composition RusoAlso were prepared by vacuum arc melting in a 
protective argon atmosphere. Disc shaped specimens (@%3x1 mm) for oxidation were prepared by 
spark machining, mechanical polishing (final stage with 0.01 pm diamond suspension) and 
ultrasonic cleaning in ethyl alcohol. 
Isothermal oxidation experiments were performed in flowing synthetic air in a temperature range 
between 1000°C and 1300°C from 1 to 50 hours. Thermogravimetric weight gain analysis were 
« Messung von carried out in a Netzsch STA-409 instrument. The samples were heated in an Al,O3 crucible at 
Coz ist ZU 20°C/min to the desired temperature. 
en der Bilder After the oxidation experiments, the surface and the cross sections of the samples were examined 
ad noch auf with the Scanning Electron Microscope (SEM) and the oxide layer analysed with an Energy 
ben muss Eine Dispersive Spectroscopy (EDS). Prior to and after oxidation the samples were characterised using 
var uch X-ray diffraction (XRD) in a Siemens D-5000 Difractometer coupled with a high temperature 
dabei auf camera (HTK) with a local OED-50M resolution detector. Focus Ion Beam (FIB) was also used to 
il on und produce a wedge form cross-section in the oxidation layer. 
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