Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10620221 | Acta Materialia | 2013 | 11 Pages |
Abstract
The equiaxed solidification of Al-20 wt.% Zn alloys revealed an unexpectedly large number of fine grains which are in a twin, or near-twin, relationship with their nearest neighbors when minute amounts of Cr (1000Â ppm) are added to the melt. Several occurrences of neighboring grains sharing a nearly common ã1Â 1Â 0ã direction with a fivefold symmetry multi-twinning relationship have been found. These findings are a very strong indication that the primary face-centered cubic Al phase forms on either icosahedron quasicrystals or nuclei of the parent stable Al45Cr7 phase, which exhibits several fivefold symmetry building blocks in its large monoclinic unit cell. They are further supported by thermodynamic calculations and by grains sometimes exhibiting orientations compatible with the so-called interlocked icosahedron. These results are important, not only because they provide an explanation of the nucleation of twinned dendrites in Al alloys, a topic that has remained unclear over the past 60Â years despite several recent investigations, but also because they identify a so far neglected nucleation mechanism in aluminum alloys, which could also apply to other metallic systems.
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Güven Kurtuldu, Philippe Jarry, Michel Rappaz,