Effects of Ni addition on the order–disorder transitions of Fe–Pt intermetallic compounds: An experimental study on Fe–Ni–Pt phase diagrams

Abstract

The Fe–Pt based intermetallic compounds exhibit good chemical stability and unique magnetic properties, where Ni is an important additional element to optimize the magnetic properties or obtain the outstanding catalytic performances of the Fe–Pt based alloys. Knowledge of how Ni addition affects the order–disorder transitions of the Fe–Pt intermetallics is thus necessary; however, the related information is limited. Therefore, in this work, the phase diagrams of the Fe–Ni–Pt system were experimentally investigated, and as a result, the isothermal sections of the Fe–Ni–Pt system at 600 and 900 °C, as well as the vertical sections of Fe80Ni20–Pt80Ni20 and Fe50Pt50–Ni50Pt50 were constructed. Based on these results, the influences of Ni addition on the crystal stabilities and phase transformations of the ordered Fe–Pt intermetallics have been well described. The results show that the L10-FePt and L10-NiPt phases form a ternary continuous solid solution of L10-(Fe,Ni)Pt, whereas Ni can dissolve in the L12-Fe3Pt and L12-FePt3 phases as high as 57.0 at.% and 26.0 at.% at 600 °C, respectively. The selective occupancy of Ni atoms has been predicted, which should depend on the alloy composition. For both the L10-(Fe,Ni)Pt and L12-FePt3 phases, when Pt contents are less than their stoichiometric values, Ni atoms will preferentially occupy the Pt sublattice, forming as many nearest-neighbor Fe−Pt bonds as possible. All these results can correlate the alloy compositions, annealing temperatures and crystal structures to both magnetic and catalytic properties, thus providing a basis for optimizing the Fe–Ni–Pt alloys towards enhanced magnetic or catalytic performances.