Experimental study and thermodynamic re-assessment of the binary Fe–Ta system

Abstract

a b s t r a c tPhase relations and thermodynamic properties in the binary FeeTa system were re-assessed taking into account available and new experimental data. Seven alloys with different chemical composition were prepared. Both, as-cast and annealed samples were analyzed by means of DTA, SEM/EDX and XRD techniques in order to experimentally verify the phase relations in the system. The experimental results showed congruent melting of the Laves phase (l), two eutectic reactions L 4 (dFe) þ l, L 4 (Ta) þ m and one peritectic reaction L þ l 4 m. Samples with 45.1, 52.3 and 56.2 at. % Ta seem to contain small amounts of the metastable Ta 3 Fe 2 phase, the fractions being too small to be identified by conventional Xray diffraction.The enthalpies of formation of solid FeeTa alloys referred to bcc-Fe and bcc-Ta at 298 K were determined by isoperibolic dissolution calorimetry using liquid Ni at 1773 K as solvent.A new thermodynamic description of the binary FeeTa system was obtained by CALPHAD modeling of the Gibbs energy of all individual phases, taking into account the above experimental data as well as assessed published data. Calculations of the phase diagram and of thermodynamic properties were performed with the Thermo-Calc software. They are shown to properly reproduce experimental data.

Thermodynamic modeling of the Ca–In and Ca–Sb systems supported with first-principles calculations

“…The reason of the deviation of enthalpies of formation from first-principles calculations to the experimental data is not clear. The case is similar to that in the binary Ni-Sc [42], Y-Ni [43], Fe-Nb [44] and Fe-Ta [45] systems. Besides, due to the lack of the measured enthalpies of formation for the compounds Ca 2 Sb and CaSb 2 , the data from the first-principles calculations could be used to provide the referable start values for the thermodynamic optimization.…”

Effect of long-term ageing on microstructure stability and lattice parameters of coexisting phases in intermetallic Ti–46Al–8Ta alloy

“…3 shows the isopleth for 8 at.% Ta of the TieAleTa systems covering the Al composition in the range of 20e70 at.% calculated using new thermodynamic description and Thermo-Calc software. The description based on CALPHAD modelling of the Gibbs energy of all accepted individual phases [16,18,19] takes into account experimental evidence of the s-phase as well as new phase equilibria observed in the aged Tie46Ale8Ta (at.%) alloy and CALPHAD modelling of the Gibbs energy of all accepted individual phases [16,18,19]. According to the phase diagram, it is expected that the microstructure of the studied Tie46Ale8Ta (at.%) alloy should transform to the equilibrium g þ s type during long-term ageing below 870 C. However, further experiments are still required to refine the position of the boundary between a 2 þ g þ s and g þ s phase regions.…”

Fabrication of magnetocaloric La(Fe,Si)13 thick films

“…The formation of the latter two phases due to diffusion between the main layer and the buffer and capping layers during the annealing process is supported by a literature report on the binary Ta-Fe systems. 14 No NaZn13type phase was detected after annealing 5.3 μm thick films below 973 K (data not shown). Note that the NaZn13-type phase was only detected in films of thickness greater than 2 µm, and that the volume content of this phase was maximum in the 5.3 μm thick films.…”