Effects of Implantation Temperature on the Structure, Composition and Oxidation Resistance of Sic
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ZUNDE YANG,* HONGHUA DU,* MATTHEW LIBERA,* AND IRWIN L. SINGER** *Department ofMaterials Science and Engineering, Stevens Institute of Technology, Hoboken, NJ 07030 "**ChemistryDivision, Naval Research Laboratory, Washington, D.C. 20375
ABSTRACT ca-SiC crystals were implanted with aluminum to a high dose at room temperature or 800'C. Studies by transmission electron microscopy showed that SiC was amorphized by room temperature implantation but remained crystalline at 800'C. Crystalline aluminum carbide was formed and aluminum redistribution took place in SiC implanted at 800'C. Implanted and unimplanted crystals were oxidized in I atm flowing oxygen at 1300°C. Amorphization led to accelerated oxidation of SiC. The oxidation resistance of SiC implanted at 800'C was comparable to 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.
INTRODUCTION Ion implantation offers a versatile means to modify the surface chemistry and structure of ceramics and hence the potential to improve their oxidation resistance, surface hardness, fracture toughness, and bend strength.' 4 From the oxidation resistance point of view, improvement can not be achieved, however, if amorphization takes place and implant concentration is low.5' 6 One method of eliminating implantation-induced amorphization is to implant a heated target.7 However, hot implantation nay lead to segregation of implants toward the sample surface, lowering the dose retention and reducing the degree of enhancement of oxidation resistance.' Broadening the scope of our early investigation at only 500 0 C implantation,9'," 0 this study examines in detail the chemistry, structure and oxidation behavior of SiC implanted with Al at a high fluence with implantation temperature as a parameter.
EXPERIMENTAL PROCEDURE 6H polytype single crystal a-SiC (0001) grown by the Acheson furnace method was polished to a mirror surface finish with 0.25 pma diamond paste. Ion implantation of SiC with A[+ ions was performed at NRL using a Varian/Extrion high current implanter at 87 keV to fluences of 2.4x1017 ions/cm2 . The projected range and straggling values are about 110 nm and 44 nm respectively, and the peak concentration is about 20 at.%, according to PROFILE" simulation. The incident angle of the ion beam was 7 degrees normal to sample surface to avoid channeling. During implantation, substrates were either heat sunk on a well-cooled substrate holder (T
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