Ivona Černičková

A Study of Phase Equilibria in the Al–Pd–Co System at 700 ∘C

Al68Pd14.6Co17.4, Al69.8Pd13.8Co16.4, Al72Pd12.8Co15.2, Al73.8Pd11.9Co14.3, and Al76Pd11Co13 alloys annealed at 700 ∘C for 2000 h were studied. In the investigation, scanning electron microscopy including energy dispersive X-ray spectroscopy and electron backscatter diffraction, X-ray diffraction, and transmission electron microscopy were used. Altogether five near-equilibrium phases (β, U, Al5Co2, e, Al9Co2) were identified. Transitions between β, U, and e phases were also determined dependent on the alloy bulk metal composition. The experimental results were used to propose the partial isothermal section of the Al–Pd–Co phase diagram at 700 ∘C. The maximum solubilities at 700 ∘C of Pd in Al9Co2 and Al5Co2 were determined as 1.7 and 2.69 at.%, respectively.

Contribution to thermodynamic description of Al-Pd system

The homogeneity range around the Al3Pd stoichiometry, representing the family of quasicrystalline approximants denoted as n and/or (Al3Pd), was involved in the calculated Al-Pd phase diagram. The calculations were performed by means of the CALPHAD method using the Thermo-Calc software. A novel thermodynamic description of the n/(Al3Pd) phase was proposed based on the (Al%,Pd)3(Al,Pd%)1 two-sublattice model. Existing thermodynamic parameters of stoichiometric phases Al4Pd and Al21Pd8 were slightly adjusted. The transition between phases n/(Al3Pd) and γ-Al21Pd8 was predicted thermodynamically at 619°C.

Microstructure Similarities between Phases F and U in Al-Pd-Co Alloys

The work is aimed at searching for compositionally variant isostructural mutations of the cubic F-phase in both as-annealed (850°C/500 h) and DTA-cooled conditions of the Al72Pd9Co19 alloy. Recently, the mutations were reported for the U-phase in the Al69.8Pd13.8Co16.4 alloy annealed at 700°C for 2000 h. In the investigation, scanning electron microscopy including energy dispersive X-ray spectroscopy, powder X-ray diffraction, and differential thermal analysis (DTA) were used. Two isostructural mutations of the F-phase, FL (the product of L-parent) and FV (the product of V-parent), were identified (symbol L stands for liquid). On DTA-cooling, the bivariant heterogeneous transition (Lpart→V), the monovariant heterogeneous transformation (Lrest→V+FL), and the monovariant quasi-eutectoid transformation (Vrest→Al5Co2+FV) were recorded.

Evolution of Phases in Selected Al–Co–Cu Complex Metallic Alloys Under Near-Equilibrium Conditions at 800–1150 ∘C

This work is focused on the experimental investigation of intermetallic phases in Al60Co29Cu11, Al63Co24Cu13, and Al67Co20Cu13 complex metallic alloys at near-equilibrium conditions. The alloys were long-term annealed at temperatures between 800 and 1150 ∘C and subsequently rapidly cooled to fix their high-temperature microstructures. Annealing temperatures were chosen with respect to the results of differential thermal analysis. Particular samples were studied by X-ray diffraction, scanning electron microscopy including energy dispersive X-ray spectroscopy and electron backscatter diffraction, and transmission electron microscopy. In the microstructures of particular samples, various combinations of D, B2, m, Al5Co2, and Θ-Al2Cu phases were identified depending on both bulk metal composition and thermal history.

Complex metallic alloys - microstructure characterization

The recent findings related to binary and ternary structurally complex phases in selected complex metallic alloys coming under Al-Pd-Co, Al-Cu-Co, and Al-Mn-Fe systems are presented. The phases were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, high-angle annular dark-field imaging, X-ray diffraction, and differential thermal analysis. There are highlighted some unusual features of phases D, U, T, and ε-family from both structural and compositional points of view.

Formation of Structurally Complex U-Phase in Al72Pd12.8Co15.2 Alloy

The U-phase in the Al72Pd12.8Co15.2 alloy was studied under non-equilibrium (casting, differential thermal analysis) and near-equilibrium (long-term annealing) conditions to consider its compositional homogeneity. In the investigation, scanning electron microscopy including energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, and differential thermal analysis were used. Contrary to the finding reported for the Al69.8Pd13.8Co16.4 alloy, the results obtained for the investigated Al72Pd12.8Co15.2 alloy did not confirm the compositional heterogeneity of the near-equilibrium U-phase after annealing at 700°C for 2000 h and at 850°C for 500 h.

A Study of Phase Transformations in Complex Metallic Alloys Al73Mn23Pd4 and Al73Mn21Pd6

The microstructure characterization of Al73Mn23Pd4 and Al73Mn21Pd6 alloys was done after annealing at 900°C for 312 h and subsequent water quenching, as well as after thermal cycling. DTA and EDX/WDX/SEM techniques were used in the investigation. It was found out that the alloys consist of the single ternary T-phase after annealing and water quenching. The DTA experiment confirmed the stability of this phase also at lower temperatures. After DTA, the alloys exhibited double-phase microstructure consisting of the ternary T-phase and probably the icosahedral I-phase. It was proved an incongruent transformation of the ternary T-phase into the liquid and vice versa.