On the binary phases ~YNi4 and Y2Ni7
Chem.
Met. Alloys 11 (2018)
92-99
https://doi.org/10.30970/cma11.0375
Volodymyr BABIZHETSKYY, Oksana MYAKUSH, Volodymyr LEVYTSKYI, Bogdan KOTUR, Viola DUPPEL, Lorentz KIENLE
Y–Ni
alloys in the composition range 79-81 at.% Ni,
annealed at 600°C and 800°C, were investigated by complementary analytical
techniques providing chemical and structural information. In contradiction to
former reports, the ~YNi4 phase was not observed at these
temperatures. The samples annealed at 600°C consisted of two phases: the rhombohedral HT β‑Y2Ni7
phase (structure type β‑Gd2Co7, space group R-3m)
and YNi5 (structure type CaCu5, space group P6/mmm).
At 800°C the hexagonal LT form α‑Y2Ni7
(structure type Ce2Ni7 type, space group P63/mmc) was found to coexist with HT β-Y2Ni7.
The transformation β‑Y2Ni7 ↔ α‑Y2Ni7
is very sluggish and increasing the annealing time to five months increased the
amount of α-Y2Ni7 only up to ~23%. The
transformation β‑Y2Ni7 ↔ α‑Y2Ni7
occurs at T > 800°C,
but a more precise determination was not possible. The ~YNi4 phase
exists in a very narrow temperature range: it
forms by the peritectic reaction YNi5 + L ↔ ~YNi4
at 1338±2°C and decomposes by the metatectic reaction ~YNi4 ↔ L + YNi5 at 1328±2°C. The section YNi5–Y2Ni7
of the phase diagram of the binary Y−Ni system
was revised consequently.
PED [100] zone axis patterns recorded on single
crystalline areas of Y2Ni7 in the Y20Ni80
sample annealed at 600°C and HRTEM micrograph with
inserted multislice contrast simulations.
Keywords
Intermetallics / Phase diagram
/ Crystal structure / X-ray diffraction