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Positron lifetime measurements have been performed in binary Fe_3Al and Fe_3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have been calculated by using the positron lifetime parameters. Density of valence electron is low in the bulk of Fe_3Al alloy. It indicates that, the 3d electrons in a Fe atom have strong-localized properties and tend to form covalent bonds with Al atoms, and the bonding nature in Fe_3Al is a mixture of metallic and covalent bonds. The density of valence electron is very low in the defects of Fe_3Al grain boundary, which makes the bonding cohesion in grain boundary quite weak. The addition of Si to Fe_3Al gives rise to the decrease of the densities of valence electrons in the bulk and the grain boundary thus the metallic bonding cohesion. This makes the alloy more brittle. The addition of Nb to Fe_3Al results in the decrease of the ordering energy of the alloy and increases the density of valence electron and th
Positron lifetime measurements have been performed in binary Fe_3Al and Fe_3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have been calculated by using the positron lifetime parameters. Density of valence electron is low in the bulk of Fe_3Al alloy. It indicates that the 3d electrons in a Fe atom have strong-localized properties and tend to form covalent bonds with Al atoms, and the bonding nature in Fe_3Al is a mixture of metallic and covalent bonds. The density of valence electron is very low in the defects of Fe_3Al grain boundary, which makes the bonding cohesion in grain boundary quite weak. The addition of Si to Fe_3Al gives rise to the decrease of the densities of valence electrons in the bulk and the grain boundary thus the metallic This makes the alloy more brittle. The addition of Nb to Fe_3Al results in the decrease of the ordering energy of the alloy and increases the density of valen ce electron and th