Morphology of M23C6 precipitation in L12-ordered Ni3(Al, Cr)

A transmission electron microscope investigation has been performed on the morphology of M₂₃C₆ precipitation in L1₂-ordered Ni₃(Al, Cr) containing 0.1–0.5 mol% of carbon. By aging at temperatures around 1073 K after solution annealing at 1423 K, fine octahedral-shaped precipitates of M₂₃C₆ bounded by {111} facets appear first on the dislocations and then in the matrix. The shapes of the precipitates are not always equilateral but tetragonal or elongated octahedral ones appear during aging. Planar growth faults were observed in some of the octahedral precipitates. After prolonged aging or by aging at higher temperatures, these shapes of precipitates become unstable. The M₂₃C₆ precipitates then adopt a rod-like morphology elongated parallel to the 100 directions and characterized by steps bounded by {111} facets.     

Temporal evolution of the nanostructure of Al(Sc,Zr) alloys: Part I – Chemical compositions of Al3(Sc1−xZrx) precipitates

Atom-probe tomography (APT) and high-resolution transmission electron microscopy are used to study the chemical composition and nanostructural temporal evolution of Al₃(Sc_1−xZr_x) precipitates in an Al–0.09 Sc–0.047 Zr at.% alloy aged at 300 °C. Concentration profiles, via APT, reveal that Sc and Zr partition to Al₃(Sc_1−xZr_x) precipitates and Zr segregates concomitantly to the -Al/Al₃(Sc_1−xZr_x) interface. The Zr concentration in the precipitates increases with increasing aging time, reaching a maximum value of 1.5 at.% at 576 h. The relative Gibbsian interfacial excess of Zr, with respect to Al and Sc, reaches a maximum value of 1.24 ± 0.62 atoms nm⁻² after 2412 h. The temporal evolution of Al₃(Sc_1−xZr_x) precipitates is determined by measuring the time dependence of the depletion of the matrix supersaturation of Sc and Zr. The time dependency of the supersaturation of Zr does not follow the asymptotic t^−1/3 law while that of Sc does, indicating that a quasi-stationary state is not achieved for both Sc and Zr.     

Energy of formation, lattice parameter and bulk modulus of (Ni,X)Ti alloys with X = Fe, Pd, Pt, Au, Al, Cu, Zr, Hf

An analysis of the ternary ‘bridge’ Ni_50−yX_yTi₅₀ alloys with X = Fe, Pd, Pt, Au, Al, Cu, Zr, and Hf was performed using the BFS method for alloys. The lattice parameter, bulk modulus and energy of formation were determined for all the intermediate states in the (B2) transition NiTi to XTi.