title: Spiral two-phase dendrites.
abstract: We present real-time observations of a new growth pattern called a spiral two-phase dendrite, which we observed during univariant directional solidification of a ternary-eutectic alloy. Two different crystal phases grow from the apex of a parabolic finger, forming a spiral pattern that leaves behind in the solid a double helix microstructure. The parabola tip radius is nearly equal to the helix step. These lengths vary approximately as the reciprocal of the square root of the tip growth velocity. The direction of growth is not selected, but is initial-condition dependent.
authors.affiliation: INSP, UPMC Univ. Paris 6, CNRS UMR 7588, 140 rue de Lourmel, 75015 Paris, France. akamatsu@insp.jussieu.fr
authors.forename: Silvère
authors.initials: S
authors.lastname: Akamatsu
authors.forename: Mikaël
authors.initials: M
authors.lastname: Perrut
authors.forename: Sabine
authors.initials: S
authors.lastname: Bottin-Rousseau
authors.forename: Gabriel
authors.initials: G
authors.lastname: Faivre