Characterization of microstructures, mechanical properties, and oxidation behavior of coherent A2 + L2₁Fe-Al-Ti

Abstract

Two Fe-Al-Ti alloys with coherent aFe,Al (A2) + Fe 2 AlTi (L2 1 ) microstructures have been produced and the evolution of the microstructure with aging time has been studied by light optical and scanning electron microscopy and hardness measurements. The compressive flow strength, creep properties, brittle-to-ductile-transition temperatures (BDTT), and oxidation behavior of the alloys have been evaluated. The results show that the investigated alloys show good flow strength, high creep resistance, and good oxidation resistance. However, their BDDT is high compared to binary Fe-Al-based alloys and compared to other Fe-Al-Ti alloys no increase in creep resistance was achieved by generating coherent microstructures. The latter effect is due to the breakup of the coherent microstructures when the temperature varies because the compositions and consequently the volume fractions of the phases vary markedly depending on temperature.

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

“…As noted above, some of the curves show a sudden change in the slope in that a higher stress exponent is observed at low strain rates while a lower stress exponent is observed at high strain rates. Such sudden changes in the stress exponent have been described before for Fe-Al-based alloys and have been attributed to changes in the microstructure [25][26][27].…”

Corrosion behaviour of Fe–Al(–Ti) alloys in steam

“…In contrast, Fee21Ale10Ti has a coherent A2 þ L2 1 microstructure with a size of the phases of a few nm. Within this aligned fine-scaled matrix few ((1 vol.%) particles of a third phase e presumably C14 Laves phase e of 1 mm are observed [14]. In the case of the ternary Ti-containing alloys the mass gains of both samples are different.…”

L21-ordered Fe–Al–Ti alloys

“…1d). Alloy Fe-21Al-10Ti contains additional C14 Laves phase which precipitated during the heat treatment predominately along grain boundaries [10]. It is noted that the volume fractions of L2 1 and A2 in the coherent microstructures are strongly dependent on temperature [10].…”

“…In this figure the flow stresses of the single-phase L2 1 (Fe-25Al-15Ti-xCr) and two-phase L2 1 þ Laves phase and L2 1 þ TiB 2 (Fe-25Al-16Ti-2B and Fe-25Al-20Ti-xCr) are combined in a single curve since they show similar flow stress behaviour [8]. A condensed single flow stress curve is also drawn for the two-phase alloys (Fe-21Al-10Ti, Fe-23Al-8.5Ti) with coherent L2 1 /A2 interfaces [10]. In addition, the flow stress of binary single-phase D0 3 (Fe-26Al) [14] and binary coherent A2 þ D0 3 [15] are shown.…”

“…Moreover, in the Fe-Al-Ti system it is possible to combine different mechanisms because they are available within a limited range of compositions. The present paper summarises results of the high-temperature strength and ductility of Fe-Al-Ti alloys with Ti and Al contents which range from 8.5 to 20 and 21-25 at.% (all compositions in at.%), respectively, and which owe their strength to increased order, boride or Laves phase precipitates [7][8][9], or coherent L2 1 þ A2 microstructures [9,10] or combinations thereof. Some of the alloys also contain Cr or B in solid solution or TiB 2 precipitates to possibly enhance ductility.…”