A similar observation was made by Taufour et al. Mn 5Rh 2Bi 4 (cubic, Fm m), with a Curie temperature of 266 K. (1974 ) identified a ferromagnetic compound, i.e.
Rh, which forms an intermetallic phase with Bi that is isotypic with α-BiMn (Ross & Hume-Rothery, 1962 Kainzbauer et al., 2018 ). A possible approach to circumvent these problems was considered to be the addition of a third component, e.g. One promising candidate is the intermetallic phase α-BiMn unfortunately, it has not been possible to synthesize this phase as a single-phase bulk material in spite of intensive research ( e.g.
Both phases under discussion have analogous structural motifs.įor decades, there has been an ongoing search for ferromagnetic materials free of rare earth elements. The linkage results in a layer structure for RhMnBi 3, while in the case of Rh 6Mn 5Bi 18, a three-dimensional network is formed the latter, however, contains several areas where Bi⋯Bi distances suggest van der Waals interactions. In both crystal structures, the units formed by the transition metal atoms are enveloped by Bi atoms, which themselves form a loosely bound network. In the Rh 6Mn 5Bi 18 structure, the transition metal atoms are linked into ribbon-like structural units aligned along the direction, whereas planar sheets are formed in RhMnBi 3. Rh 6Mn 5Bi 18, with a Wyckoff sequence a f2 g2 i5, crystallizes in the tetragonal system (space group P4 2/ mnm Pearson symbol tP58), and RhMnBi 3, with a Wyckoff sequence a c g i q, crystallizes in the orthorhombic system ( Cmmm oS20). Their crystal structures represent new structure types. hexarhodium pentamanganese octadecabismuthide (Rh 6Mn 5Bi 18) and rhodium manganese tribismuthide (RhMnBi 3). Alloys that had ratios greater than 1 were largely composed of δ phase precipitates, whereas a ratio less than 1 resulted in the predominance of the η phase precipitates.A study of the ternary Rh–Mn–Bi phase diagram revealed the existence of two new ternary bismuthides, viz. For alloys in which δ and/or η phase precipitates were formed, the prevalent phase could be determined by evaluating the compositional ratio for (Nb+Ta)/(Al+Ti). When the alloy chemistry was observed to exhibit a compositional ratio of Al/(Nb+Ta+Ti) less than 1, δ and/or η phase precipitates formed, whereas a ratio greater than 1 resulted in conventional γ-γ′ microstructures. A set of experimental alloys was investigated to understand the formation of the δ and η phase precipitates in Ni-base superalloys. As the effects of these phases on high-temperature mechanical properties are not well quantified, a better understanding of the thermodynamics and kinetics associated with the formation of these δ and η phase precipitates is required for future designs of Ni-base superalloys. While compositional changes enabled the formation of the δ phase precipitates, in some alloys an additional precipitate phase η was formed. Recent investigations have focused on the development of polycrystalline, ternary eutectic γ-γ′-δ Ni-base superalloys that use large volume fractions of the intermetallic δ phase to provide composite strengthening.
In response to the increasing temperature capability of the structural materials required for advanced gas turbine engines, new alloying concepts are required to develop materials with properties that are significantly better than existing nickel-base superalloys. Precipitate Phase Stability in γ-γ′-δ-η Ni-Base Superalloys Precipitate Phase Stability in γ-γ′-δ-η Ni-Base Superalloysĭetrois, Martin Antonov, Stoichko Helmink, Randolph Tin, Sammy