Precipitation of A1N in High Purity Fe-Al-N Alloy
1971 Volume 57 Issue 6 Pages 978-985
Details
1971 Volume 57 Issue 6 Pages 978-985
High purity Fe-Al-N alloys were prepared using zone-refined iron (>99.99%), and precipitation process of AlN from solid solution was studied. Two kinds of specimens were prepared, one was assolution-treated and the other was as cold-worked after solution treatment of 1 250°C×1hr. Afterthese specimens were annealed isochronally, the electrical resistivities were measured in liquid nitrogen.
The result shows that large decreases of the resistivity are found in the temerature range from 400°Cto 700°C, and the temperature of the decrease shifts to a lower side as the specimens are cold-worked.
The specimens as solution-treated were isothermally annealed at the temperature range from 600°C to 700°C, where the large decrease of the resistivity was noted in the isochronal annealing, and theirelectrical resistivity and internal friction were measured. The results obtained are as follows;
(1) Activation energy of this process is found 53 kcal/mol.
(2) In this process exists some incubation period for nucleation.
(3) The apparent order of this chemical reaction γ derived from -dn/dt=nγK is found to beabout unity.
(4) Normalized resistivity change coincides with normalized change of N Snoek peak.From these results, it may be deduced that the large decrease of the resistivity can be attributed tothe precipitation of AlN, that the rate of the process is controlled by the diffusion of Al atoms in airon, and that the process can be expressed by an equation of chemical reaction, Al+NAIN, with unequal initial concentrations of reactants. The last deduction was confirmed by experiments of alower Al content alloy (Fe-0.02 Al-N).
