William Stratton Ph.D. Thesis - MINDS@UW Home

ability 35 because it results in the highest Trg 20,35,36 . Probably the most attractive property of
these amorphous alloys is their high tensile strengths 16,34 for their weight. Melt-spun ribbons of
these alloys have tensile strengths approaching 1000 MPa 37 , but this can easily increase to 1500
MPa 25 when the material is brought through partial crystallization and becomes a nanocrystal /
amorphous composite. A similar phenomena is seen in Fe glasses (e.g. Metglass), where the
devitrification reaction creates α-Fe nanocrystals resulting in excellent soft magnetic properties
17,26,28 .
High Al-content amorphous alloys can be formed by rapid quenching (melt-spinning) 38
or by severe plastic deformation (cold-rolling) 19,39 . In melt-spinning a master ingot is melted
and ejected under high pressure onto a cold wheel spinning at a high speed in an inert
atmosphere, producing a thin ribbon of amorphous alloy at cooling rates up to 10 5 K/s. Cold-
rolling is deformation by rolling and folding (> 100 times) of a multilayer sandwich of high
purity metallic foils, increasing the total strain, defect density, and interfacial volume until an
amorphous state is achieved 12,19,40 . The intense deformation process can also be accomplished
by ball milling which makes an amorphous powder 41 .
When annealed below Tg, high Al-content amorphous alloys exhibit an interesting
devitrification behavior. Upon annealing of the rapidly quenched material, α-Al nanocrystals
form at very high concentrations (> 10 20 m -3 ) in the amorphous material 12,19 . These nanocrystals
form from the amorphous material with a higher solute concentration than the eutectic alloy 15 ,
unlike the eutectic favored by other systems. During devitrification these nanocrystals quickly
grow to tens of nm, and then stop growing due to an increase in the diffusion barrier for Al
caused by the ejection of RE or TM from the nanocrystal into the amorphous matrix 12,19 . These
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