The structural and electrocatalytic properties of metastable Ni-Mo alloys have been investigated for the hydrogen evolution reaction in alkaline solutions. Amorphous and nanocrystalline phases have been prepared by mechanically alloying the elemental components under various milling conditions. Fcc nanocrystals are formed when the Mo concentration is smaller than 30 at. %. The nanocrystalline state becomes unstable with respect to the amorphous phase when the Mo content in the solid solution exceeds 30 at. %. The electroactive phase for the hydrogen evolution reaction in alkaline solutions is the nanocrystalline supersaturated solid solution. The presence of oxygen during the milling process improves the properties of the alloys.

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The TiAl and the TiSi system are chosen as model systems to study the origin of metastable phase formation during mechanical alloying of elemental powder blends with a negative heat of mixing. The results demonstrate that kinetics play only a minor role in the phase selection, in particular for the final state. Instead, the intermetallic phases are energetically destabilized with respect to the solid solutions and the amorphous phase due to the destruction of the chemical long‐range order upon milling. Thus the latter phases tend to form during mechanical alloying of elemental poweder belnds as well as during milling of powders of the stable intermetallic compounds. The metastable phases can be predicted by the free energy curves which are calculated by the CALPHAD method. In case of the TiAl and TiSi alloys, metastable structures and grain sizes in the nm range can be obtained which promise improved mechanical behaviour with respect to the processing of light‐weight intermetallic compounds for high‐temperature applications.

The Ti–Si system is chosen as a model system to study the mechanical alloying of elemental powder blends in which one of the components is brittle. In addition, the stability of intermetallic compounds upon milling is investigated, in order to interpret the metastable phase formation during the milling process. Detailed x-ray investigations show that during mechanical alloying, a solution of Si in Ti preceeds the formation of amorphous or intermetallic phases. The selection of phases formed, as well as the final state, are influenced by the overall composition of the powder blends, and by the milling procedure applied. However, predictions can be made by considering the free energy curves of the stable and metastable phases in the Ti–Si system, which have been calculated by the CALPHAD method. Milling of the intermetallic compounds generally leads to the same final state as the mechanical alloying of elemental powder blends with corresponding compositions. These results demonstrate that the intermetallic compounds are energetically destabilized upon milling, allowing for phase transformations into metastable phases, such as amorphous or metastable crystalline alloys. The energetic destabilization of intermetallic compounds mainly originates from the chemical disorder caused by the milling process.

The solid-state reaction in Ti/Cr multilayered diffusion couples at temperatures between 450 and 650 "C was investigated by x-ray diffraction. It was found that an amorphous phase is formed at a concentration around 55 at. % Cr. The results are in excellent agreement with those obtained from mechanically alloyed powders, and with the corresponding metastable phase diagram calculated by the calculation of phase diagrams method. The observations strongly suggest that inverse melting is possible in the Ti-Cr system at around 55 at. % Cr.