Nitrogen solubility and aluminum nitride precipitation in liquid iron, Fe-Cr, Fe-Cr-Ni, and Fe-Cr-Ni-Mo alloys |
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Authors: | Harue Wada and Robert D Pehlke |
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Affiliation: | (1) Department of Materials and Metallurgical Engineering, The University of Michigan, 48109 Ann Arbor, MI |
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Abstract: | The nitrogen solubility and aluminum nitride formation in liquid Fe-Al, Fe-Cr-Al, Fe-18 pct Cr-8 pct Ni-Al and Fe-18 pct Cr-8
pct Ni-Mo-Al alloys were measured by the Sieverts' method. The temperature range extended from 1823 to 2073 K, and the aluminum
contents from 1.01 to 3.85 wt pct Al. Increasing aluminum content increases the nitrogen solubility. The effect of molybdenum
additions was determined for 2, 4 and 8 wt pct Mo levels. The first and second order effects of chromium, nickel, molybdenum
and aluminum on the activity coefficient of nitrogen in iron were determined. The first and second order effects of chromium,
nickel and molybdenum on the activity coefficient of aluminum also were determined. The nitride precipitates were identified
as stoichiometric aluminum nitride, AIN, by X-ray diffraction analysis. The lattice spacing was in good agreement with the
ASTM standard patterns for AIN in both higher and lower Al content solutions. The solubility product of AIN increases with
increasing aluminum concentration and with temperature in liquid iron and the iron alloys studied. However, the magnitudes
of the solubility products of AIN in those alloys are different because of the effects of chromium and nickel additions. Additions
of molybdenum show little effect on the solubility product of AIN. The standard free energy of formation of AIN in liquid
iron is: δG‡ = -245,990 + 107.59 \T J/g-molAIN, based on the standard state of the infinitely dilute solution in liquid iron
for aluminum and nitrogen, referred to a hypothetical one wt pct solution, and on the pure compound for A1N. |
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