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Since the original paper is behind a paywall (at least for me), can anyone explain the specifics of what the researchers did to produce this new alloy? >> Dr K

Since the original paper is behind a paywall (at least for me), can anyone explain the specifics of what the researchers did to produce this new alloy? >> Dr Kim and his colleagues have, however, found that a fifth ingredient, nickel, overcomes this problem. I'd imagine that it didn't take a world-class team of scientists to have come up with the idea of alloying using nickel. There is no way materials scientists and metallurgists hadn't tried this by now, so what did they do differently?

cataphract 12y ago
Since this is mostly undecipherable for me, I'll just quote: «A common method of uniformly distributing fine particles in a matrix is to make the best use of highly potent nucleation sites for inducing the precipitation of the particles. In this study, potential nucleation sites for B2 during annealing of wrought sheet steel include (1) grain boundaries or edges of recrystallized austenite crystals and (2) deformation shear bands, which are common in hot- or cold-worked low-density steel. To expand the stability domain of B2 above the recrystallization temperature (normally, 800–900 °C) of deformed austenite, the alloying recipe of an austenitic low-density steel was modified by adding 5 weight per cent nickel (Ni), which is one of the most effective elements for forming B2 with aluminium. The addition of Ni to low-density steel may appear to conflict with the collective wisdom of ferrous alloy design; Ni has been regarded merely as a well-known austenite stabilizer like Mn and C; and Ni has been little noticed in low-density steel design, mainly because it is not a critical determinant of the density in ferrous alloys.» (citations omitted)
rsfern 12y ago
Materials Science PhD student here, I'll do my best. The morphology of the brittle B2-FeAl intermetallic compound is the key. In the conventional lightweight steel alloys, the B2 intermetallics make the alloy brittle (so they don't work harden very well), so in the past researchers optimized their alloys to avoid forming these intermetallics [0]. The nickel promotes the nucleation of the intermetallic particles during heat treatment [1], so that you get a more-or-less uniform distribution of many nanocrystalline B2 particles, instead of a smaller number of larger or more clustered B2 domains. The small B2 particles contribute to strain hardening by pinning dislocation motion, without reducing the ductility of the alloy. From the Nature letter: [0]: "One of the general concepts employed until now in the alloy design of Fe-Al-Mn-C-based, high-aluminium, low-density steel has been the suppression of ‘brittle’ intermetallic compound formation by stabilizing the ‘ductile’ austenite matrix." [1]: "To expand the stability domain of B2 above the recrystallization temperature (normally, 800–900 °C) of deformed austenite, the alloying recipe of an austenitic low-density steel was modified by adding 5 weight per cent nickel (Ni), which is one of the most effective elements for forming B2 with aluminium."

cataphract 12y ago

Since this is mostly undecipherable for me, I'll just quote: «A common method of uniformly distributing fine particles in a matrix is to make the best use of highly potent nucleation sites for inducing the precipitation of the particles. In this study, potential nucleation sites for B2 during annealing of wrought sheet steel include (1) grain boundaries or edges of recrystallized austenite crystals and (2) deformation shear bands, which are common in hot- or cold-worked low-density steel. To expand the stability domain of B2 above the recrystallization temperature (normally, 800–900 °C) of deformed austenite, the alloying recipe of an austenitic low-density steel was modified by adding 5 weight per cent nickel (Ni), which is one of the most effective elements for forming B2 with aluminium. The addition of Ni to low-density steel may appear to conflict with the collective wisdom of ferrous alloy design; Ni has been regarded merely as a well-known austenite stabilizer like Mn and C; and Ni has been little noticed in low-density steel design, mainly because it is not a critical determinant of the density in ferrous alloys.» (citations omitted)

rsfern 12y ago

Materials Science PhD student here, I'll do my best. The morphology of the brittle B2-FeAl intermetallic compound is the key. In the conventional lightweight steel alloys, the B2 intermetallics make the alloy brittle (so they don't work harden very well), so in the past researchers optimized their alloys to avoid forming these intermetallics [0]. The nickel promotes the nucleation of the intermetallic particles during heat treatment [1], so that you get a more-or-less uniform distribution of many nanocrystalline B2 particles, instead of a smaller number of larger or more clustered B2 domains. The small B2 particles contribute to strain hardening by pinning dislocation motion, without reducing the ductility of the alloy. From the Nature letter: [0]: "One of the general concepts employed until now in the alloy design of Fe-Al-Mn-C-based, high-aluminium, low-density steel has been the suppression of ‘brittle’ intermetallic compound formation by stabilizing the ‘ductile’ austenite matrix." [1]: "To expand the stability domain of B2 above the recrystallization temperature (normally, 800–900 °C) of deformed austenite, the alloying recipe of an austenitic low-density steel was modified by adding 5 weight per cent nickel (Ni), which is one of the most effective elements for forming B2 with aluminium."