Influence of Ir Additions and Icosahedral Short Range Order (ISRO) on Nucleation and Growth Kinetics in Au-20.5Wt Pct Cu-4.5Wt PctAg Alloy

Julien Zollinger (1) , B. Rouat (1) , J. Guyon (2) , S. K Pillai (1) , M. Rappaz (3)

1 IJL - Institut Jean Lamour
2 LEM3 - Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux
3 EPFL - Ecole Polytechnique Fédérale de Lausanne

Based on detailed EBSD analyses, Kurtuldu et al [1] have explained the grain refinement of Au-12.5 wt.%Cu-12.5 wt.%Ag (yellow gold) by the addition of minute amounts of Ir in terms of "icosahedral quasicrystal (iQC)-mediated nucleation", i.e., Ir induced the formation of Icosahedral Short Range Order (ISRO) of atoms in the liquid, leading to the formation of iQC on which the fcc-phase forms. In the present contribution , we show that: (i) this mechanism is also responsible of the grain refinement in Au-20.5 wt.%Cu-4.5 wt.%Ag (pink gold) with Ir addition; (ii) ISRO also influences the morphology and growth kinetics of the fcc phase: at solidification rate of a few mm/s, 100 dendrites are replaced by a cellular-type morphology growing along 111 when 100 wt.ppm of Ir is added to the melt; (iii) iQC-mediated nucleation is accompanied by a spinodal decomposition of the liquid, which is revealed at high cooling rate by the formation of Cu-rich particles or dendrites, some of them being also twinned, in parallel to iQC-mediated grain refinement and twin formation.

Domaines: Matériaux; Science des matériaux [cond-mat.mtrl-sci]

Julien Zollinger, B. Rouat, J. Guyon, S. K Pillai, M. Rappaz. Influence of Ir Additions and Icosahedral Short Range Order (ISRO) on Nucleation and Growth Kinetics in Au-20.5Wt Pct Cu-4.5Wt PctAg Alloy. Metallurgical and Materials Transactions A, 2019, 50, pp.2279-2288. ⟨10.1007/s11661-019-05176-2⟩. ⟨hal-02050947⟩