Microstructural Evaluation During Mechanical Milling and Consolidation of ODS LI 2 -(AI,Cr) 3 Ti H. Saage, M. Heilmaier, J. Eckert and L. Schultz, Institute of Solid State and Materials Research Dresden, D-01069 Dresden, Germany, h.saage@ifw-dresden.de ABSTRACT The effect of different oxide particles on the microstructure and the high temperature creep behavior of ODS ternary L1 2 -(Al,Cr) 3 Ti intermetallic compounds, which were prepared by high ener- gy ball milling, was analyzed. Particular attention was paid to the development of the dispersoid size and distribution after the milling process, the consolidation and the heat treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) of the as-milled pow- ders indicate that the ordered matrix can nearly be amorphizied during milling. Moreover, independent of the type of oxide the dispersoids with a mean diameter • 20 nm are homogeneously distributed in the metallic matrix. Using hot pressing under protective atmosphere the powders were compacted to nearly full density, followed by heat treatment. This results in grain sizes varying between 200 nanometers and several micrometers. However, due to the nature of the dispersoids used different par- ticle diameters were found after consolidation and annealing. Although known to be the thermody- namically most stable oxide the initial Y 2 0 3 powder has formed a mixed yttrium-aluminum oxide dur- ing manufacturing and, hence, significant particle growth has been observed. While CeO 2 shows a sim- ilar behavior, the line compound A1 2 0 3 remains stable, but the average particle size of this oxide also increases during the heat treatment. First preliminary mechanical tests supported by TEM observations show the significant influence of the grain size on the creep resistance at high temperatures. INTRODUCTION Recently, it has been shown [ 1-3] that the class of ternary trialuminides of type AI 67 Ti 25 X 8 (with X = Cr, Fe, Mn, Cu, Ni, Ag) shows excellent compressive room temperature ductility due to its high- er crystal symmetry (ordered L1 2 -structure) as compared to the binary A1 3 Ti intermetallic compound (tetragonal D0 22 structure). Besides their low density and very good oxidation resistance a potential application of such intermetallics as high temperature structural materials particularily depends on their resistance against creep deformation. The addition of a small amount of incoherent oxide parti- cles via mechanical alloying or milling techniques can retain extraordinary creep resistance up to about 90% of the melting temperature. The choice of a suitable oxide type is defined by several fac- tors: on one hand the oxide under consideration should have a negligible solubility within the metal- lic matrix, low diffusivity of the constituent atoms in the matrix, a high negative heat of formation and a high melting point. With respect to these prerequisites, Y 2 0 3 seems to be most promising and has been used for dispersion strengthening of nickel- and iron-base superalloys, e.g. [4]. On the other hand, formation of mixed oxides (especially with Al) has been observed [5,6]. This can lead to signif- icant dispersoid growth during consolidation and annealing of the material and, hence, deteriorates the creep resistance at high temperatures. Consequently, in this paper the effect of different oxide particle types, namely Y 2 0 3 , A1 2 0 3 and CeO 2 on the microstructure and the high temperature creep behavior of ODS (AI,Cr) 3 Ti L1 2 -intermetallic compounds was analyzed. Particular attention was paid to the development of the dispersoid size and distribution after the milling process, the consolidation and the heat treatment. KK8.34.1 Mat. Res. Soc. Symp. Proc. Vol. 552 0 1999 Materials Research Society