Nadia Parodi

The Dy–Al–Si ternary system has been experimentally studied, as the effect of the dysprosium addition on the constitution and topology of the liquidus surface, focusing on the (Al) rich part. The system has been investigated in a composition range of up to about 58 at% silicon. The alloys constitution and the liquidus surface projection have been determined by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray powder diffraction (XRPD), and differential thermal analysis (DTA). This work is part of a research framework on the properties and solid–liquid phase equilibria of the R Al–Si (R: rare earth) systems. These data, along with the ternary systems isothermal section, are needed to outline the design, plan, and development of new Al–Si-based alloys. In the Dy–Al–Si system, four primary crystallization fields have been experimentally detected: (Si), DyAl_xSi_(2−x) (orthorhombic form), Dy₂Al₃Si₂ (Τ₂), and DyAl_(3−x)Si_x. The following three invariant equilibria have been identified: at 566 °C the ternary eutectic L ⇆ DyAl₂Si₂ + (Al) + (Si), at 630 °C the U₁ L+ DyAl₃ ⇆ Dy₂Al₃Si₂ + (Al), and at 562 °C the U₂: L+ Dy₂Al₃Si₂ ⇆ DyAl₂Si₂ +(Al) reactions. A comparison with other known R Al–Si systems has been conducted.