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 NiAl 3, Ni 2Al 3, NiAl and Ni 3Al 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 τ 1 and τ 3 have been observed. The τ 1 phase has a composition very close to Ni 4AlSi and τ 3 (Ni 3(Al 1− x Si x ) 7) has been analyzed to have a lower Si content. A new ternary phase Al(Ni)Si 4(τ 4) 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.