Über Kristallstruktur und Ordnung aus der Schmelze abgeschreckter Legierungen des Systems Kupfer-Zinn
✍ Scribed by H.J. Seemann; H. Knödler
- Publisher
- Elsevier Science
- Year
- 1959
- Weight
- 783 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0001-6160
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✦ Synopsis
formation of zones Al in-C% alloys. It therefore seems reasonable to suggest that the zones contain extra rows of copper atoms. These rows would lie in 110 type directions. Each extra row of atoms may be thought of as a pair of edge dislocations of opposite sign in the matrix, one above and one below the zone, spaced apart a distance equivalent to the thickness of the zone. The Burgers vectors would be of the type and magnitude i(l IO}. The increase in resistivity according to this model would be due to scattering of electrons by the extra rows of atoms as well as the lattice strains in the matrix. The following rough calculation indicates that this suggestion is quite reasonable.
A~cor~g to Barer and Bever@) the resistivity of an Al-2 at..:& Cu alloy decreases about 20% due to precipitation at 250°C where the stable precipate forms. This is due to removing copper from solid solution.
According to Fink and Smith,c2) the resistivity decreases about 1.5% during aging for a long time at room temperature. Thus, in a specimen well-aged at room temperature the resistivity at room ~mperature is roughly 18.50/, higher than the resistivity of the matrix alone. The resistivity is about 4 ,uQ-cm and thus about 0.7 ,uQ-cm is attributable to scattering of conduction electrons by zones.
The resistivity from the extra rows of copper atoms and the lattice strains should be comparable to that from the imagined grid of edge dislocations in the zone-matrix interfaces. Since the mismatch is roughly 12%, a grid of edge dislocations spaced about 8 atom diameters apart would be required. The number of dislocations per cm2 of zone-matrix interface would equal 2.3 x 101a. In a 2 at,% Cu alloy, assuming all of the copper atoms to be in zones one atom thick, there would be roughly 1.5 x 1013 dislocation lines threading each cm2 of alloy. According to the experimental determination of Wintenberger,cg) in pure aluminum the resistivity per dislocation line per cm2 is 2.2 x lo-r4 @-cm. Using this figure, a resistivity of 0.33 @&cm is estimated for the extra resistivity or about half of the experimental value. The agreement between the two values indicates that there may be some validity in our assunlption of extra rows of copper atoms in the zones.
If these extra rows of copper atoms do exist, they could also contribute to the hardening since cutting of zones during plastic deformation would necessitate creation of jogs in these extra rows. This would be analagous to the case of the necessity for cutting dislocations which thread the slip plane.