Alumina–alloy nanocomposite powders by mechanosynthesis

Mossbauer spectroscopy and X-ray diffraction were used to investigate the synthesis of nanocomposite powders by reactive milling of a variety of blends 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 in the iron-rich part of the ternary with chromium in the 0.18–0.20 range were also investigated. The essential steps of the reaction mechanisms were identified as functions of milling time and initial composition. A number of transient phases, some metastable under normal conditions at room temperature were observed. Chemical heterogeneities and their changes in the metallic phases were also characterized semi-quantitatively and the possibility of side effects, such as partial dissolution of not yet reacted Cr2O3 into newly formed Al2O3, was considered. Finally, some of the as-milled powders were subsequently heat treated for 1 h at 1100 °C to explore their structural changes and progress towards homogenization via the same experimental techniques. © 1998 Kluwer Academic Publishers