Low-energy ball milling of amorphous Fe78B13Si9 has been performed at temperatures between 25 and 250 °C. Primary crystallization is observed after milling at elevated temperatures, but not after annealing at the same temperatures. Although milling at room temperature creates nucleation sites for primary crystallization, subsequent annealing at elevated temperature does not result in significant crystallization. Heating by ball impact and contamination by the milling tools during milling are ruled out as the causes for crystallization. The observed behavior is interpreted to be caused by diffusivity enhancement due to milling-produced defects.

The mechanical alloying process in the immiscible Ni-Ag system with a positive heat of mixing was investigated by x-ray diffraction and differential scanning calorimetry. High energy ball milling of mixed elemental powders, with nominal composition Ni x Ag 100Ϫx (x ϭ 95, 90, 70, 50, and 30͒, results in the formation of mixtures of supersaturated, nanocrystalline Ni-rich and Ag-rich solid solutions. The solubilities and final grain sizes of these phases depend on the nominal composition of the powder. The maximum solubilities were determined using Vegard's law to be 4.3 at. % Ni in Ag and 6.6 at. % Ag in Ni for samples milled at room temperature. The effect of milling temperature on mechanical alloying was examined in the range Ϫ195 to 250°C. Lower temperature milling leads to a larger solubility of Ni in the Ag-rich samples, up to 7.1 at. % for the Ni 30 Ag 70 composition. Indications for the existence of a concentrated solid solution (Ni 36 Ag 64-Ni 44 Ag 56) were also found. Milling at higher temperatures leads to lower solubilities. A study of the thermal stability of supersaturated Ag-rich and Ni-rich phases shows that milling at high temperature can be understood in terms of a competition between mechanical mixing and thermal decomposition. At room temperature, nonequilibrium vacancies are responsible for decomposition. The results give new insight into the general characteristics of the mechanical alloying process in thermodynamically unstable systems.

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Zirconia-rich subsolidus phase relationships in the Zr0,-Sc,O, and ZrO,-In,O, systems were investigated. Phase inconsistencies in the Zr0,-Sc,O, system resulted from a diffusionless cubic-to-tetragonal (t') phase transformation not being recognized in the past. Through three different measuring techniques, along with microstructural observations, the solubility limits of the tetragonal and cubic phases were determined.

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