Structure, strength and toughness of nanocrystalline FeAl

Refining grain size to the nanocrystalline level has been suggested as a way of improving strength while enhancing ductility and toughness. In the present study, nanocrystalline bulk FeAl has been prepared by mechanical alloying and hot forging. Powders quickly reach a state of partial order during milling, and low temperature annealing is sufficient to chemically homogenise and give full order. Contamination during milling leads to the formation of carbide and oxide particles, which stabilise fine grains during heating. Bulk materials show grain sizes of 20nm to 100nm depending on the consolidation temperature. Hardness and compression strength show little change over this grain size range. Fracture toughness stays high down to moderately small grain sizes, falling only for consolidation at the lowest temperatures. There appears to be a reasonable range of fine grain sizes (40–100nm) where good interparticle bonding and high densities can be achieved leading to good strength and toughness.