Effects of implantation temperature on the structure, composition, and oxidation resistance of aluminum-implanted SiC
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a - S i C crystals were implanted with aluminum to a high dose at room temperature or 800 °C. Transmission electron microscopy showed that SiC was amorphized by room temperature implantation but remained crystalline after 800 °C implantation. Crystalline aluminum carbide was formed and aluminum redistribution took place in SiC implanted at 800 °C. Implanted and unimplanted crystals were oxidized in 1 atm flowing oxygen at 1300 °C. Amorphization led to accelerated oxidation of SiC. The oxidation resistance of SiC implanted at 800 °C was comparable with that of pure SiC. The oxidation layers formed on SiC implanted at both temperatures consisted of silica embedded with mullite precipitates. The phase formation during implantation and oxidation is consistent with thermodynamic predictions. The results from our current and earlier studies suggest that there exists an optimum range of implantation temperature, probably above 500 °C but below 800 °C, which preserves the substrate crystallinity and retains the high aluminum dosage, for the enhancement of oxidation resistance of SiC.
I. INTRODUCTION Ion implantation offers a versatile means to modify the surface chemistry and structure and, hence, the surface sensitive properties of ceramics. Documented studies have demonstrated many benefits of implanting ceramics, including improved oxidation resistance, surface hardness, fracture toughness, and bend strength.1"4 These enhanced properties can be lost, however, if the surface becomes amorphous and implant concentration is low. 56 One method of eliminating implantationinduced amorphization is to implant "hot", that is, to implant into a heated substrate.7 This approach has been taken to investigate the influence of Ti + ions or Al + ions on the surface mechanical properties of SiC and Si 3 N 4 implanted to high fluences and at high temperatures,8"10 and, more recently, on the oxidation behavior of Al + and Cr + ions implanted into SiC.1-1112 However, hot implantation may also lead to segregation of implants toward the sample surface, lowering the dose retention and reducing the degree of enhancement of surface properties.10 Our studies of Al implantation at 500 °C indicated that the implanted SiC remained single crystalline, although some residual lattice damage was present.1-11 No apparent Al redistribution was observed in the implanted region. The oxidation resistance of SiC implanted with Al at this temperature was enhanced up to 45%, compared with unimplanted crystals.1'12 J. Mater. Res., Vol. 10, No. 6, Jun 1995 http://journals.cambridge.org
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Broadening the scope of our early investigation limited to only 500 °C implantation, 11112 this study examines in detail the chemistry, structure, and oxidation behavior of SiC implanted with Al at a high fluence with implantation temperature (i.e., room temperature and 800 CC) as a parameter. Near-surface compositions were analyzed by Auger electron spectroscopy (AES). Microstructural and phase characteristics were obtained by cross-sectional transmissi
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