Microstructure and Deformation Behaviour of Iron‐Rich Iron‐Aluminium Alloys with Ternary Carbon and Silicon Additions

Abstract

The microstructure, hardness, yield stress, fracture strain, and brittle-to-ductile transition temperature of Fe-AI alloys with AI contents of 12 -18 at.% AI, which are in the range of the so-called K-state with possible short-range ordering reactions, and with ternary additions of carbon and silicon were studied with respect to the effects of possible impurities on the hardening of Fe-AI alloys. It was found that perovskite-type Fe~IC carbide particles precipitate even in alloys with low C and Si contents; they are controlled by prior heat treatments and strongly affect the deformation behaviour.

Fe–Al materials for structural applications at high temperatures: Current research at MPIE

“…In continuation of earlier work at MPIE [112 -114] the microstructures and mechanical properties of Fe 3 Al-based alloys with precipitates of the j-phase Fe 3 AlC x were thoroughly evaluated [89,100,115]. While some improvement of the room-temperature ductility was observed, no improvement of the strength at high temperatures could be attained due to fast coarsening of the Fe 3 AlC x precipitates.…”

Concepts derived from phase diagram studies for the strengthening of Fe–Al-based alloys

“…The solid solubility for carbon in a-(Fe,Al)/FeAl changes only slightly between 800 and 1200 8C but is considerably lower at lower temperatures, e.g. drops from about 1 at.% C at 1000 8C to about 50 ppm at 320 8C [18,63]. This leads to the precipitation of fine needle shaped precipitates of the K phase at the grain boundaries during cooling.…”

“…This leads to the precipitation of fine needle shaped precipitates of the K phase at the grain boundaries during cooling. As the carbon diffusivity is even high at ambient temperatures, these precipitates at the grain boundaries are found at room temperature in all alloys of appropriate compositions even after quenching and they do strongly affect mechanical properties at low temperatures [18,63].…”

Atom probe tomography investigation of heterogeneous short-range ordering in the ‘komplex’ phase state (K-state) of Fe–18Al (at.%)

“…As such, it is expected that C in solid solution will not have a significant effect on the SRO measured in the current case. Since C diffusivity is still high at ambient temperatures, these grain boundary precipitates are found at room temperature in all alloys of appropriate composition, even after quenching, strongly affecting mechanical properties at low temperatures [71,81]. No grain boundaries or associated carbide precipitates were captured in the current results, but it is suspected that their presence may have negatively affected experimental atom probe data yield during voltage-pulsed operation at cryogenic temperature.…”

“…Whilst the solid solubility for carbon in a-(Fe,Al)/FeAl changes only slightly between 800 and 1200 C, it is considerably lower at lower temperatures, e.g. drops from about 1 at.% C at 1000 C to about 50 ppm at 320 C [71,81]; and this leads to the precipitation of fine, needle-shaped precipitates of the k phase at the grain boundaries during cooling [9,23]. As such, it is expected that C in solid solution will not have a significant effect on the SRO measured in the current case.…”