The Al–Ni–Si phase diagram between 0 and 33.3 at.% Ni

The ternary Al–Ni–Si phase diagram between 0 and 33.3 at.% Ni was investigated by a combination of differential thermal analysis (DTA), powder X-ray diffraction (XRD), metallography and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the respective equilibrium phases were determined within the isothermal section at 550 °C by means of EPMA. Al3Ni2 and NiSi2 were found to form extended ternary solid solutions while Al3Ni and the ternary phase Al6Ni3Si have only small homogeneity ranges within the ternary system. The variation of lattice parameters with the composition was studied for all solid solution phases. DTA was used to investigate ternary phase reactions. A total number of five invariant reactions could be derived from DTA data, i.e. one ternary eutectic reaction, three transition reactions and one ternary peritectic reaction. All experimental data were combined to yield a ternary reaction scheme (Scheil diagram) of the investigated composition range and a liquidus surface projection was constructed based on DTA results. The melting behavior of the extended solid solution phase NiSi2−xAlx was studied in detail by DTA measurements at low heating rates. The melting reaction was found to change from peritectic decomposition in the binary Ni–Si system to congruent melting at approximately 20 at.% Al.