Formation of intermetallic compounds in the Ni–Al–Si ternary system

Abstract

Phase equilibria in the Ni–Al–Si system have been studied in the temperature range 550 °C using a ternary diffusion couple experiment with pure Ni and an Al–Si eutectic alloy. A number of binary and ternary intermetallic compounds have been observed. The intermetallics NiAl₃, Ni₂Al₃, NiAl and Ni₃Al form as solid layers just above pure Ni. Each of the binary intermetallics has some solubility for Si, which replaced Al in the ordered lattices. Two ternary intermetallics τ₁ and τ₃ have been observed. The τ₁ phase has a composition very close to Ni4AlSi and τ₃ (Ni₃(Al₁−_XSix)7) has been analyzed to have a lower Si content. A new ternary phase Al(Ni)Si₄(τ₄) has been observed in the diffusion couple heat treated for longer times at 550 °C. The morphology of the binary and ternary phases is presented.