Determination of the isothermal sections of the Al-Ni-Si ternary system at 750 °C and 850 °C
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The phase equilibria of the Al-Ni-Si ternary system at 850 °C and 750 °C have been investigated using scanning electron microscopy (SEM) and electron-probe microanalysis (EPMA). Isothermal sections at 850 °C and 750 °C were constructed based on experimental data from 53 alloys heat treated at 850 °C for 1200 hours and at 750 °C for 1440 hours, respectively. The phase equilibria among the following intermetallics and solid-solution phases are described: Ll2-Ni3(Al,Si), B2-NiAl, Ni5Si2, δ-Ni2Si, ϑ-Ni2Si(τ 4), Ni3Si2, NiSi, NiSi2, Ni2Al3, NiAl3, Ni2AlSi(τ 2), Ni3Al6Si(τ 3), Ni16AlSi9(τ 5), the fcc solid solution, and the diamond (Si) phase. In addition, a phase, temporarily designated as Ni5(Al,Si)3(τ 6), was observed for the first time at both 750 °C and 850 °C. This phase is probably the stabilization of Ni5Al3 by Si to higher temperatures than the binary Ni5Al3, which is only stable at <∼700 °C.
KeywordsMaterial Transaction Isothermal Section Gray Phase Alloy Heat Equilibrium Microstructure
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