Mechanical properties of silicon ion implanted and annealed sapphire and polycrystalline alumina

Abstract

Ion implantation of silicon ions into sapphire and polycrystalline alumina followed by heat treatment resulted in the precipitation of mullite. A dose of 1 × 10¹⁸ Si⁺ /cm² followed by a heat treatment at 1400‡ C produced an interlocking mullite surface layer with a needle morphology which was identifiable by x-ray diffraction (XRD). The lower thermal expansion coefficient of mullite compared to alumina produces a compressive surface layer on cooling from the annealing temperature and is evidenced by observations of Vickers indentations. Annealing at 1400‡ C resulted in a 30% increase in fracture toughness for sapphire and more importantly, an increase of 30% was also observed for polycrystalline alumina substrates. The effect of silicon implantation on the microhardness of sapphire and on the modulus of rupture of implanted polycrystalline alumina was also measured and is reported.