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In present work, a multiphase Ni 3 Al-based intermetallic alloy with complex components of γ'+γ dendrite comprising extremely high volume fraction (81 vol %) of γ′ phase and interdendritic β phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 °C/s), air cooling (AC, 72 °C/s), and furnace cooling (FC, 0.05 °C/s) after solution treatment at 1200 °C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary γ′ as well as size of spherical secondary γ′ particles in the γ'+γ dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary γ′ particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic β phase resulted from different cooling methods, i.e., the rod-like Cr 3 C 2 carbides, the semi-spherical α-Cr particles, and the long acicular γ′ precipitates. The lower cooling rate decreases the number of rod-like Cr 3 C 2 carbides, increases the number and size of the semi-spherical α-Cr particles, and promotes the formation of long acicular γ′ precipitates in the interdendritic β-matrix. The semi-spherical α-Cr particles play the role of pinning dislocations in the β-matrix and have the orientation relationship of [‾110] α-Cr //[‾110] β-matrix. In addition, the precipitation of semi-spherical α-Cr particles in β-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of α-Cr particles due to the nanotwins in β-matrix. Microtwins are observed in the interdendritic β-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, γ′-envelope formed between the γ'+γ dendrite and interdendritic β phase dependent on the solution cooling processes. Image 1 • Re-precipitation sizes of primary and secondary γ′ particles have the logarithmic relationship with solution cooling rates. • Microtwins in the β-matrix have a bimodal configuration of nanotwins at their boundary and interior stacking faults. • Precipitation pattern and growth mode of semi-spherical α-Cr particles in β-matrix phase after air cooling. • Precipitation behaviors influenced by solution cooling rates of precipitates in the interdendritic β. [ABSTRACT FROM AUTHOR]

A CoNi-based alloy (various cooling rates after solution heat treatment) was utilized to investigate the microstructure-dependent coarsening behavior of γ′ precipitates. The fast cooling rate leads to the formation of initial fine γ′ precipitates with high number density. The different initial microstructures of CoNi-based alloy lead to various coarsening behaviors of γ′ precipitates during subsequent aging treatment at 900 °C. The coarsening behavior of large γ′ precipitates with low density (formed in slow cooling rate, 0.1 °C/s) is in accordance with the Lifshitz-Slyozov-encounter modified (LSEM) model. Whereas for the fine γ′ precipitates with high density (formed in fast cooling rate, 60 °C/s or 240 °C/s), its coarsening behavior is consistent with the TIDC model at early stage and LSEM model at later stage, respectively. • The different initial microstructures of Cobalt-based alloy lead to various coarsening behaviors of γ′ precipitates. • Fast cooling rate leads to the formation of fine γ′ precipitates with high density. • Coarsening of fine γ′ precipitates is consistent with the TIDC model in the early stage and LSEM model in the later stage. • Coarsening of large γ′ precipitates is in accordance with the LSEM model. [ABSTRACT FROM AUTHOR]

The Nb 3 (Al 1-x Sn x) superconductors (x = 0.05, 0.15, 0.25, 0.35) were prepared by mechanical alloying and subsequent low-temperature sintering. It was found that the critical current density (J c) of the obtained Nb 3 (Al 1-x Sn x) sample is enhanced significantly compared to undoped Nb 3 Al prepared using the same method. The maximum value of the J c reaches up to 5.10 × 104 A·cm−2 (4.2 K, 5 T) for Nb 3 (Al 0.85 Sn 0.15) sample. Combined with the phase composition analysis and microstructure observation, it is indicated that Sn enters the A15 crystal structure of Nb 3 Al forming the Nb 3 (Al 1-x Sn x) phase after low-temperature sintering. What's more, Sn doping improves the grain connectivity as well as refines the grain size of Nb 3 Al, which are the main reasons for the enhancement of J c in the Sn doped samples. Based on the exploration of the phase evolution of Nb–Al–Sn system during the mechanical alloying and subsequent low-temperature sintering process, it is also confirmed that Nb 3 Sn forms firstly during the sintering process and then can serve as the perfect nucleus of Nb 3 Al to increase its nucleation rate, leading to the significant decrease of the grain size of Nb 3 Al. • The J c of Nb 3 Al reaches up to 5.10×104 A·cm−2 (4.2 K, 5 T) after Sn doping. • The Sn doping sharply reduced the grain size of Nb 3 Al (from 80-200 nm to 25–40 nm). • During the low-temperature sintering process, the Nb 3 Sn formed firstly and then served as the perfect nucleus of Nb 3 Al to increase its nucleation rate. [ABSTRACT FROM AUTHOR]