Exploitable results
During the project significant progress has been made in the understanding of the parameters influencing the formation of nanocrystalline materials by crystallization of glassy precursors. Amorphous phase separation prior to any crystallization event is supposed to be responsible for "nanocrystallisation". The stability of nanocrystalline structures against grain growth was studied in a number of (Fe,Co)33Zr67 alloys. The ideal grain growth model can be applied, but the exponent has been found between 0.2 and 0.3, far below the ideal 0.5.
These results were presented at the ISMANAM-96 conference in Rome and are published within the proceedings.
The improvement of electrochemical properties (i.e. the hydrogen overpotential) in nano-crystalline Ni-Mo alloys as mentioned in the literature results more likely from the oxygen contamination during ball-milling than from the nanocrystalline structure. Methods like ion implantation of oxygen or plasma-spraying are supposed to be promising techniques to prepare advanced electrodes for hydrogen production by electrolysis. In only partially crystallized Ni70Mo10B20 and Ni70Mo10P20 glasses, however, excellent low hydrogen overpotentials have been observed.
A significant increase of strength as well as microhardness has been observed in a number of nanocrystalline (Ni,Mo)-B, (Ni,Mo)-P as well as Zr33(Fe,Co)67 alloys prepared by crystallization of glassy precursors. The observed brake-down of the Hall-Petch relationship at very small grain diameter could be attributed to the presence of a small amount of the remaining amorphous matrix.
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