MICROSTRUCTURE AND THERMOCHEMISTRY OF ION-IMPLANTED SINTERED ALUMINA

The topic of this work consists in performing high-dose metallic ion implantations (Zr, Fc and Cu) into industrial polycrystalline alumina. The use of complementary techniques allows a physico-chemical and structural analysis of the implanted surfaces, before and after thermal treatments performed at various temperatures in air. The techniques used are nuclear methods (Rutherford backscattering spectrometry - RBS, conversion electron Mossbauer spectroscopy - CEMS), grazing-angle X-ray diffraction (GXRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopies (SEM and TEM). The chemical and structural analysis permits a comparison of the reactivity of the different implanted species with alumina. Zirconium, iron and copper are respectively detected as Zr0 and Zr(IV) (ZrO2), Fe0 (small alpha-Fe precipitates), Fe(II) (FeAl2O4) and Fe(IV) (metastable phase), Cu0 (small metallic precipitates) in the implanted region. Thermal treatment of implanted alumina between 600 and 1600-degrees-C leads to strong chemical modifications. A complete oxidation of the implanted layer is observed between 600 and 1000-degrees-C. Annealing at higher temperatures leads to a significant surface composition evolution: phase transformation of tetragonal ZrO2 into monoclinic ZrO2, formation and growth of FeAlO3, Fe2O3, Fe3O4, CuO and CuAl2O4 precipitates. The presence of the detected phases is discussed in terms of equilibrium thermochemical reactions between Zr (Fe, Cu) and Al2O3, as described by ternary phase diagrams. The objective of the discussion is to demonstrate how binary and ternary phase diagrams can provide guidelines for interpreting and predicting the composition of high-dose ion-implanted ceramics, before and after thermal annealing. The formation of metal-ceramic and ceramic-ceramic composites with specific compositions and structures can thus be accurately controlled by both implantation and post-implantation thermal treatment parameters.