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

• Phase diagrams of the Fe–Ni–Pt system were constructed by diffusion triple combined with key alloys. • Effects of Ni addition on the ordering transitions of Fe–Pt Intermetallic compounds have been well described. • Ni decreases the thermodynamic stabilities of all Fe–Pt intermetallic compounds. • A selective occupancy of Ni atoms in the L 1 0 -(Fe,Ni)Pt and L 1 2 -FePt 3 phases has been first proposed. 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 Fe 80 Ni 20 –Pt 80 Ni 20 and Fe 50 Pt 50 –Ni 50 Pt 50 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 L 1 0 -FePt and L 1 0 -NiPt phases form a ternary continuous solid solution of L 1 0 -(Fe,Ni)Pt, whereas Ni can dissolve in the L 1 2 -Fe 3 Pt and L 1 2 -FePt 3 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 L 1 0 -(Fe,Ni)Pt and L 1 2 -FePt 3 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. [Display omitted] [ABSTRACT FROM AUTHOR]