α-NiPt(Al) and phase equilibria in the Ni–Al–Pt system at 1150 °C

The α-NiPt(Al) phase and its associated equilibria in the Ni–Al–Pt system at 1150 °C were investigated by analyzing equilibrated bulk alloys and the interdiffusion zones of diffusion couples. Phase constitutions, tie-lines and microstructures were determined using a combination of techniques, including high-energy synchrotron X-ray diffraction, scanning electron microscopy and electron probe microanalysis. A large Pt solubility limit was found to exist in the β-NiAl, ∼42 at.%, and in γ′-Ni3Al, ∼32 at.%. The α-NiPt(Al) phase was found to have wide Pt solubility range of about 33–60 at.% and to skew along an almost constant Pt/Al ratio of 1.5. The α-NiPt(Al) has an ordered face-centered tetragonal L10 crystal structure, with the Al and Pt atoms found to be preferentially located in the corners and prismatic faces, respectively. The temperature dependence of the lattice parameters and unit cell volume of the α phase were also determined.