Ultra-fine microstructures formed by annealing in Al- and Fe-base amorphous alloys and their mechanical properties

Aluminum- and iron-base amorphous alloys were crystallized by isochronal annealing, and their mechanical properties were measured as a function of the grain size. The results obtained in both alloys are summarized as follows: 1) The tensile strength shows the maximum value when the 20 similar to 30 vol% of the specimens is crystallized. By further annealing, these alloys become very brittle, and the strength abruptly decreases. The strength, however, increases again when the grain size reaches 50 similar to 100 nm in diameter. 2) In these brittle materials, the effect of grain size on the strength was estimated by comparing the maximum tensile strength with microhardness. 3) Microhardness increases up to the maximum value when the specimens are fully crystallized with grains of 10 nm in diameter, and then gradually decreases with increasing grain size. 4) The alloys with grain sizes 50 similar to 100 nm in diameter are thermally stable, and show the strength higher than those of the amorphous alloys. The mechanical properties of both alloys are discussed as a function of grain size which is closely related with guest elements exhausted from the primary crystals.