Microstructural Characterization of Al 2 O 3 Following Simultaneous Triple Ion Bombardment
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MICROSTRUCTURAL CHARACTERIZATION OF Al203 FOLLOWING SIMULTANEOUS TRIPLE ION BOMBARDMENT J. ZINKLE* S.*Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6376 USA ABSTRACT The through-range microstructure of polycrystalline alumina has been examined by cross-section TEM following simultaneous implantation of 2.0 MeV Al+, 1.44 MeV 0+, and 0.2 to 0.4 MeV He+ ions at room temperature to a dose of 3.1 keV/atom. The specimen remained crystalline following the irradiation, and four distinct radiation-induced defect features were observed: Network dislocations, dislocation loops, small cavities, and oblong clusters that may be aluminum colloids. The microstructure near the implanted ion region was qualitatively similar to that observed in irradiated regions far from the implanted zone. INTRODUCTION Ion implantation of ceramics such as A12 0 3 has received a considerable amount of attention in recent years [1-3]. Ion implantation is being studied as a means for improving properties such as wear resistance and fracture toughness near the surface of ceramics, and is also convenient for fusion reactor radiation effects studies. Most of the emphasis has been directed toward determining conditions that produce amorphization. The specimen temperature and chemical species of the implanted ion are recognized to be important experimental parameters for producing the amorphous state. Implantations conducted near or above room temperature often do not cause A120 3 to become amorphous, whereas implantation at liquid nitrogen temperatures can produce amorphous alumina for damage energies of less than 1 keV/atom [1,3]. It has been reported that alumina implanted at room temperature can be amorphized by Zr ions for damage levels >5 keV/atom, whereas implantation to similar doses with any of 13 other ions did not produce the amorphous state [1]. On the other hand, some studies suggest that alumina may be amorphized at room temperature by several different ion species for damage levels of about 5 keV/atom [2,4]. The microstructure of alumina irradiated at room temperature is examined in this study in an attempt to gain some understanding of the microstructural changes induced by implantation. Ion irradiation studies in metals have established that injected ions can have a large influence on the resultant microstructure [5]. Therefore, cross-sectional analysis techniques were used to examine the depth dependence of the irradiated region. High energy ions were employed so that the implanted ion region could be distinctly separated from regions where only displacement damage occurred. The chemical effects associated with the implanted ions were minimized by simultaneous implantation of Al+ and 0+ ions in a nearly stoichiometric ratio. Helium was also injected during the irradiation in order to study the effects of gas on microstructural development. EXPERIMENTAL PROCEDURE Polycrystalline alumina specimens (grain size = 30 pm) were irradiated as mechanically polished transmission electron microscope disks in a 9specimen array. Th
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