The model was broadened to include binary and ternary hydrides of known hydrogen concentration.
Literature Review.
(i) A STUDY OF NANOCRYSTALS.
A thermodynamic model based on the wetting topological disorder at the grain boundaries, has been proposed for the nanocrystal to glass transition of ball milled metallic powders. It was found that when a critical nanograin size and a certain amount of supersaturation are attained, am amorphous layer may be formed at the nanograin boundary. For a lower nanograin size an instability of capillary origin leads to complete or partial amorphization of the sample. The aim of the present study is to extend this model to the crystal-amorphous transition those intermetallics can undergo when they are subjected to mechanical grinding.
When the nanograin size is attained under grinding, the high density of dislocations created at the nanograin boundaries facing nanocrystals can be moled by an amorphous layer. In other terms it is equivalent to the nanograins being wetted with a topologically disordered layer. The definition of the thermodynamic conditions which must be fulfilled in order for such a disordered layer to form at the nanograin boundaries constitutes the main aim of this work.
(ii) THE THERMODYNAMIC MODEL.
For a situation where a bicrystal, presenting a grain boundary of large disorientation of free energy (ogb), is in contact with a glassy phase of the same composition (the grain boundary is considered here as being a sharp interface extending over one or two interatomic distances). If sigma designates the free energy of the interface between the crystal and the amorphous phase, the classical necessary condition to be satisfied in order for a glassy layer to be form at the grain boundary is the following:.
ogb > 2* o.
The quantity Sp= ogb - 2* o is the spreading coefficient which measures the wetting driving force.
(iii) THE MIEDEMA MODEL.
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