The Al–Ni–Si phase diagram. Part II: phase equilibria between 33.3 and 66.7 at.% Ni

The ternary Al–Ni–Si phase diagram between 33.3 at.% Ni and 66.7 at.% was investigated by a combination of differential thermal analysis (DTA), powder X-ray diffraction (XRD), metallography and electron probe microanalysis (EPMA). Ternary phase equilibria were investigated within three isothermal sections at 550, 800 and 1000 °C and the homogeneity ranges at these temperatures were determined by means of EPMA. Powder XRD was used to investigate the variation of lattice parameters with the composition for the different solid solution phases, in particular the solid solutions of Si in AlNi and of Al in δ-Ni2Si. DTA was used to identify a total number of 13 invariant ternary reactions yielding a complete description of ternary equilibrium reactions in this part of the phase diagram. A liquidus projection of the entire investigated composition range was constructed by combining our own DTA data with literature data for the limiting binary systems. The binary Ni–Si phase diagram was reinvestigated within the composition area of the high temperature phase θ-Ni2Si by means of DTA. Based on our experimental results we propose to regard ternary AlySi9−yNi13±x (τ4) and binary θ-Ni2Si as one single solid solution phase.