竹内 章

M o 3 5 N i 1 5 R h 1 5 R u 3 5 , F e 1 4 M o 3 5 N i 1 5 R h1 5 R u 2 1 , M o2 5N i2 5R h2 5R u2 5, and F e 2 0 M o 2 0 N i 2 0 R h 2 0 R u 2 0 ( a t. % ) alloys were designed b y referring t o hexagonal close-packed ( h c p ) N b - M o - R u - R h - P d high-entropy alloys ( H E A s ) reported b y Liu e t a l., with the help o f Pearson ' s Crystal Data. X-ray diffraction profiles o f the F e 2 0 M o 2 0 N i 2 0Rh2 0 R u 2 0 and F e 1 4 M o 3 5 N i 1 5 R h 1 5 R u 2 1 alloys prepared via the conventional arc-melting and subsequent annealing a t 1700 K for 1 h show a n h c p structure. Further scanning electron microscopy observations combined with elemental mapping via energy-dispersive X-ray spectroscopy confirmed the single h c p structure. The F e 2 0 M o 2 0 N i 2 0 R h 2 0 R u 2 0 H E A annealed a t 1700 K for 1 h exhibited a mixing entropy (Sm i x) normalized b y the gas constant (R ) o f 1.846, 14% higher than the configuration entropy (Sc o n f i g) normalized b y R (Sc o n f i g/R = l n 5 ) . This study reveals two new ultrahigh-mixing-entropy alloys ( U H M i x E A s ) that satisfy Sm i x > Sc o n f i g, the F e 2 0 M o 2 0 N i 2 0 R h 2 0 R u 2 0 and F e 1 4 M o 3 5 N i 1 5 R h 1 5 R u 2 1 alloys. The evaluation o f Sm i x/Sc o n f i g for the present U H M i x E A s and referential Co-containing H E A s from early studies revealed that Sm i x/Sc o n f i g of the former are constant whereas those o f the latter increase a t the magnetic transition (Curie) temperature o r below.