High-Strength Alloys Containing Nanogranular Phases


Akihisa Inoue Institute for Materials Research, Tohoku University

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Nanostructured alloys are usually produced by inert gas condensation from vapor phase, sputtering, rapid solidification of the melt, electrodeposition, or mechanical attrition severe plastic deformation of the solid phase as well as by devitrification of glassy alloys, and other techniques.

The processing procedure can be a single-step or double/multistep one. The same material can be produced by different techniques. However, the production technique often makes significant influence of the properties of nanomaterials.

If the process involves nucleation and growth, then high nucleation rate and low growth rate of the precipitating phase are required in order to obtain a nanostructure. Such conditions are usually obtained under primary devitrification with long-range, diffusion-controlled growth. For example, Al-rich amorphous alloys with high Al concentrations above 85 at.%, in general, suffer double or multistage devitrification in which the first-stage exothermic reaction is due to the precipitation of fcc-Al, and the other exothermic peaks result from the decomposition of the residual amorphous phase to intermetallic compounds. Another way of forming a nanostructure by devitrification of the metallic glasses is spinodal decomposition.