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

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.