Structure, strength and toughness of nanocrystalline FeAl

Refining grain size to the nanocrystalline level has been suggested as a wa y of improving strength while enhancing ductility and toughness. In the pre sent study, nanocrystalline bulk FeAl has been prepared by mechanical alloy ing and hot forging. Powders quickly reach a state of partial order during mining, and low temperature annealing is sufficient to chemically homogenis e and give full order. Contamination during mining leads to the formation o f carbide and oxide particles, which stabilise fine grains during heating. Bulk materials show grain sizes of 20nm to 100nm depending on the consolida tion temperature. Hardness and compression strength show little change over this grain size range. Fracture toughness stays high down to moderately sm all grain sizes, falling only for consolidation at the lowest temperatures. There appears to be a reasonable range of fine grain sizes (40-100nm) wher e good interparticle bonding and high densities can be achieved leading to good strength and toughness. (C) 1999 Acta Metallurgica Inc.