Convergent beam diffraction analysis of dispersoids in oxide dispersion strengthened alloys
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I.
INTRODUCTION
III.
IN a recent analytical electron microscopic investigation of oxide particles in commercial yttria dispersion strengthened alloys, 1 the majority of the particles were identified to be four types of yttrium-aluminum oxides. The four oxides were, (1) yttrium-aluminum garnet, YAG (5A1203 9 3Y203): cubic, a = 12.01~, 2'3 (2)yttrium-aluminum perovskite, YAP (A1203" Y203): orthorhombic, a = 5.18, b = 5.33, and c = 7.37/~, (3) YAP' (A1203 9Y203): monoclinic, 9 and (4) yttrium-aluminum monoclinic, YAM (A1203" Y203): monoclinic, a = 7.37, b = 10.47, c = 11.12,~, and /3 = 108.5~ 4,8 The YAG, YAP, and YAM oxides lie on the A1203-Y203 pseudo-binary line and have been reported to exist in some commercial ODS alloys. 10-13 Over the past several years, there has been an increasing interest in utilizing the diffraction information in High Order Laue Zones to obtain three dimensional structure, symmetry, and space group of crystals. 14,15,16The techniques and analytical procedures necessary to take full advantage of the HOLZ information have been the subject of a recent review. 17 Electron diffraction analysis of the yttriumaluminum oxides in the previous investigation indicated interesting features, and this article describes the results of the subsequent microdiffraction analysis of these oxides. Diffraction analysis of YAG and YAP oxides are discussed in this article and the analysis of YAM and the new YAP' oxides will be reported in a subsequent publication.
II.
RESULTS
The YAG and YAP particles used for microdiffraction analysis were in the range of 500 to 1500,~ in size and the probe size used for microdiffraction was about 125/~ in the TEM mode. The aluminum and yttrium concentrations of the particles were measured by X-ray microanalysis and the values agreed well with the stoichiometric concentrations of the oxides. 2-8 The results diffraction analyses of the two classes of particle are described below. YAG (5 A1203 9 3 Y203)
A Zone Axis Pattern ZAP map for YAG is shown in Figure 1_:_.An examination_ of the patterns indicated that the [012], [ 123], and [112] diffraction patterns are in accordance with the expected diffraction patterns for the body-centered cubic crystal structure, but the [001], [011], and [111] orientations showed interesting special features. Figure 2(a) shows a [001] microdiffraction pattern showing the Zero Order Laue Zone (ZOLZ) and First Order
EXPERIMENTAL PROCEDURE
A commercial oxide dispersion strengthened alloy, alloy X-127" (Ni-16.0 pct Cr-4.5 pct AI-I.0 pct Y203) was used *Supplied by Special Metals Corporation, New Hartford, New York.
to carry out diffraction analysis of YAG and YAP particles. The procedures for sample preparation are described elsewhere. 1All specimens were examined in an EM 400T/FEG electron microscope at 100 KV.
M. RAGHAVAN, Senior Staff Metallurgist, and R. PETKOVICLUTON, Group Head, are both with CorporateResearch Science Laboratories, ExxonResearch and Engineering Company,P. O. Box 45, Linden, NJ 07036. J.W. STEEDS is Professor with the Dep
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