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Transition behaviors of γ-β₀/β in V-, Cr-, Mn-doped TiAl alloys.

ABSTRACT: The behavior of γ-β/β₀ phase transition in TiAl alloy doped with β stabilizers (V, Cr, Mn) are studied by using the first principles method. It is found that alloying addition as well as anharmonic lattice vibration and disordered atomic occupation contributes to enhance the stability of cubic structure and accordingly introduce the disordered β phase into the high-temperature microstructure. The formation of low-temperature β₀ phase originates from not only the stabilization of cubic structure but also the destabilization of tetragonal structure. In particular, the latter is the main reason for the premature precipitation of the hard-brittle β₀ phase in the room-temperature microstructure at low nominal doping concentrations. We also find a special doping region in which the γ and the β phases are stable, while the β₀ phase is unstable. The existence of this region provides an opportunity for the regulation of the contents of β and β₀ phases.

SUBMITTER: Zhu L

PROVIDER: S-EPMC8102528 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:A theoretical study of geometrical structures, electronic properties, and spectral properties of single-atom transition metal-doped boron clusters MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) is performed using the CALYPSO approach for the global minimum search, followed by density functional theory calculations. The global minima obtained for the MB24 - (M = Sc, Ti, V, and Cr) clusters correspond to cage structures, and the MB24 - (M = Mn, Fe, and Co) clusters have similar distorted four-ring tubes with six boron atoms each. Interestingly, the global minima obtained for the NiB24 - cluster tend to a quasi-planar structure. Charge population analyses and valence electron density analyses reveal that almost one electron on the transition-metal atoms transfers to the boron atoms. The electron localization function (ELF) of MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) indicates that the local delocalization of MB24 - (M = Sc, Ti, V, Cr, and Ni) is weaker than that of MB24 - (M = Mn, Fe, and Co), and there is no obvious covalent bond between doped metal and B atoms. The spin density and spin population analyses reveal that open-shell MB24 - (M = Ti, Cr, Fe, and Ni) has different spin characteristics which are expected to lead to interesting magnetic properties and potential applications in molecular devices. The polarizability of MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) shows that MB24 - (M = Mn, Fe, and Co) has larger first hyperpolarizability, indicating that MB24 - (M = Mn, Fe, and Co) has a strong nonlinear optical response. Hence, MB24 - (M = Mn, Fe, and Co) might be considered as a promising nonlinear optical boron-based nanomaterial. The calculated spectra indicate that MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) has different and meaningful characteristic peaks that can be compared with future experimental values and provide a theoretical basis for the identification and confirmation of these single-atom transition metal-doped boron clusters. Our work enriches the database of geometrical structures of doped boron clusters and can provide an insight into new doped boron clusters.

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Transition behaviors of γ-β0/β in V-, Cr-, Mn-doped TiAl alloys.

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Transition behaviors of γ-β₀/β in V-, Cr-, Mn-doped TiAl alloys.