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Appendix B. Site Reports—Europe 179
nanostructured alloys, (3) mechanically alloyed superconducting
borocarbides, and (4) bulk metallic glasses.
In the first thrust the relationship to nanostructured research is that ball
milling is a nonequilibrium processing method for preparation of nanoscale
materials. In this regard the formation of nanocrystalline materials is studied
by determining grain size as function of milling conditions such as
temperature, milling intensity, and alloy composition. In terms of high
strength lightweight alloys, Al and Mg alloys with mixed phases of
nanocrystalline, amorphous, and/or quasicrystalline nanoscale
microstructures are studied. Of special interest are Al-base (> 90 at.% Al)
alloys with nanoscale quasicrystalline phases of 20-100 nm diameter
surrounded by fcc Al phase of 5-25 nm thickness. The quasicrystalline
phase comprises 60-80% volume fraction of the alloys. These alloys
combine high strength (1,000 - 1,300 MPa fracture strength) and good
ductility (6-25%). The suggested mechanisms for these excellent
mechanical properties include the thin fcc Al layer around the
quasicrystalline particles, a high density of phason defects and approximant
crystalline regions with subnanoscale size, and the spherical morphology of
the quasicrystalline particles with random orientations. The research is
aimed at a better understanding of the mechanical behavior of these
promising materials.
Bulk metallic glasses (e.g., Mg 55 Y 15 Cu 30 ) are prepared by solidification
and mechanical alloying methods. The mechanically alloyed bulk metallic
glass powders are consolidated at temperatures above T g . Again some
studies of mixed amorphous and nanocrystalline phases are carried out in
these systems. That is, the nanocrystalline precipitates are used to strengthen
the amorphous matrix.
Dr. Karl-Hartmut Müller
IFW, Institute for Metallic Materials, Department of
Superconductivity, Magnetism
Dr. Müller described the research program on the hydrogen-assisted
preparation of fine-grained rare earth permanent magnets. The technique
used is “hydrogenation disproportionation desorption recombination”
(HDDR). The final structure is fine-grained, 100-500 nm, rather than
nanoscale, but during the disproportionation and desorption steps the
structures can be ~ 100 nm in size. An example of HDDR for Nd-Fe-B is as
follows: Original cast alloy of Nd 16 Fe 76 B 8 with Nd-rich and Nd 2 Fe 14 B
phases is processed in four steps: (1) hydrogenation forms NdH 2.7 and
Nd 2 Fe 14 BH 2.9 ; (2) disproportionation reaction results in a fine mixture of Fe,
NdH 2.2 , and Fe 2 B; (3) desorption provides a very fine mixture of Fe, Nd,