“ Une actual 1 
‚Tapidly X 4). With the solidification process changes the composition of the rest of the melt to the equilibrium 
: dered ud one and the conditions approach to those at the beginning of the oxidation process shifted only to 
ud’ (iy the new position. Consequently a uniform distribution of oxide particles of a size about 100 nm 
ihe cy useful for dispersion strengthening was obtained in the regions of former IL. If the distance between 
IL is small enough (depending on the starting microstructure and IO temperature), we attain 
homogeneous distributed RE oxide particles in the o.cy matrix. 
Conclusions 
The present experiments have shown that the internal oxidation temperature, the rapidly solidified 
microstructure and its changing before the internal oxidation front strongly influence the 
mechanism of the internal oxidation process and the resulted microstructure 
Internal oxidation in the solid state takes place mainly by direct oxidation of the intermetallic 
particles and partly by dissolution of these particles ahead of the internal oxidation front and 
oxidation of the alloying element from the solid solution. 
In the semisolid state (ocutL) the internal oxidation process occurred by precipitation of the rare 
earth oxides from the liquid phase continuing with solidification of the nearest surrounding melt. 
A uniform distribution of oxide particles of a size about 100 nm useful for dispersion strengthening 
was obtained with the internal oxidation in the semisolid state. 
References 
(1) M. S. Nagorka; C. Levi; G. E. Lucas; S. D. Rider: Mat. Sci. & Eng. A 142 (1991) 227 
(2) J. R. Groza, J. C. Gibeling: Mat. Sci. & Eng. A 171 (1993) 115. 
(3) M. Ashby: Z. Metallkde. 55 (1964) 5. 
(4) J. R. Groza: JMEPEG 1 (1992) 113. 
(5) I. AnZel; A.C. Kneissl; L. Kosec; A. Krizman: Z. Metallkde., 88 (1997), 38. 
(6) W. Kurz; D.J. Fisher; Fundamentals of solidification , Trans. Tech. Aedermannsdorf, 
Switzerland, (1989). 
dhe ca matrix 20 
ms dissolve in the 
pd the cid 
gs precipitates from 
moved by QUOD 
ing increases with 
At he cred wl 
„ho arrow in Fig 
749