Alumina-alloy nanocomposite powders by mechanosynthesis

Mossbauer spectroscopy and X-ray diffraction were used to investigate the s ynthesis of nanocomposite powders by reactive milling of a variety of blend s of aluminium and metallic oxides corresponding to the target compositions : Al2O3-(Fe,Cr,Ni) alloys. Particular emphasis was given to the (Fe,Cr) and (Fe,Ni) binaries with chromium contents ranging between 0.13 and 0.60 and nickel contents between 0.10 and 0.80, respectively. Several compositions i n the iron-rich part of the ternary with chromium in the 0.18-0.20 range we re also investigated. The essential steps of the reaction mechanisms were i dentified as functions of milling time and initial composition. A number of transient phases, some metastable under normal conditions at room temperat ure were observed. Chemical heterogeneities and their changes in the metall ic phases were also characterized semi-quantitatively and the possibility o f side effects, such as partial dissolution of not yet reacted Cr2O3 into n ewly formed Al2O3, was considered. Finally, some of the as-milled powders w ere subsequently heat treated for 1 h at 1100 degrees C to explore their st ructural changes and progress towards homogenization via the same experimen tal techniques. (C) 1998 Kluwer Academic Publishers.