Mechanical properties of a forged Fe–25Al–2Ta steam turbine blade

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.

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“…The excess Gibbs free energy term in this model is expressed by RedlicheKister polynomials similar to those in Eqs. (5) and (6) Fig. 10.…”

Section: Solid Solution Phasesmentioning

confidence: 96%

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

et al. 2011

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“…[9] Recent investigations indicate that, in addition to the formation of the (Fe,Al) 2 Ta Laves phase, when Ta is added to Fe 3 Al, there is the unexpected formation of the Heusler-type phase. [12] It is not surprising, therefore, that the Fe-Al-Ta system has been studied with an emphasis on the Laves and Heusler phases, and on the relationship existing between alloy composition, phase stability, microstructure, and mechanical properties. [13,14] Another ternary, the Co-Al-Nb alloy system, exists, in which both the ternary Laves phase and the Heusler phase, Co 2 AlNb, occur.…”

Section: Introductionmentioning

confidence: 99%

Solidification Reaction Sequence of Co-Rich Nb-Al-Co Alloys

Feitosa

D’Souza

West

et al. 2017

Metall Mater Trans A

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The freezing reaction sequence of Co-rich Nb-Al-Co ternary alloys with emphasis on the formation of Laves and Heusler phases has been examined. For Co-rich alloys, the solidification reaction sequence is observed as primary freezing of a-Co and CoAl phases, subsequent [Co + C36] and [CoAl + C36] eutectics, and the final ternary eutectic reaction [L fi a-Co + C36 + CoAl]. The compositions of solidified a-Co and C36 phases agree with the corresponding vertices of the tie-triangle at the solidus temperatures. When the Nb concentration is over 20 at. pct in Co-rich alloys, the quasi-peritectic reaction [L + Co 2 AlNb fi C36 + CoAl] does not occur as equilibrium prediction. The formation of C36 and CoAl phases occurs through solid precipitation and must be distinguished from a solidification reaction.

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“…Such two-phase FeeAleTa alloys are attractive for materials development [9,11,12]. Recent investigations indicate that already small amounts of Ta result in the precipitation of the Laves phase (Fe,Al) 2 Ta and when added to Fe 3 Al, they were found to improve creep resistance through the formation of an unexpected Heusler-type phase [13,14]. Besides, Ta addition to FeeAl alloys was reported to have no detrimental effect on the excellent oxidation behaviour at temperatures between 600 and 800 C [11,16].…”

Section: Introductionmentioning

confidence: 99%