Formation of {alpha}{double_prime} iron nitride in FeN martensite: Nitrogen vacancies, iron-atom displacements, and misfit-strain energy

Journal Article · Wed Jan 01 04:00:00 EST 1997 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-997-0083-9· OSTI ID:438584

Genderen, M.J. van; Boettger, A; Mittemeijer, E J ^[1]

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1. Delft Univ. of Technology (Netherlands). Lab. for Materials Science

The precipitation of {alpha}{double_prime} iron nitride in FeN martensite (containing about 5.9 N/100 Fe) is studied as a function of tempering time successively at 333 and 373 K by means of X-ray diffractometry (XRD). On the basis of peak (=lattice parameter) shifts and intensity changes of main and superstructure reflections, it is concluded that, during tempering, the structure of the formed {alpha}{double_prime} precipitates changes. At 333 K, initially stoichiometric Fe{sub 16}N{sub 2} is formed and, with further tempering, structural vacancies are introduced, i.e., Fe{sub 16}N{sub 2{minus}x} is formed. At 373 K, the vacancies are partially filled. The change of the {alpha}{double_prime} structure at 333 K is caused by the change of the matrix from martensite to ferrite, i.e., the misfit between the {alpha}{double_prime} and the matrix is initially relatively small and then increases. By allowing nitrogen-deficient {alpha}{double_prime}, the increase of the misfit can be diminished at the expense of some increase of the volume of {alpha}{double_prime}. Gibbs free energy calculations (at 333 K), in which differences in the misfit energy are decisive, indeed show that, in a martensite matrix, Fe{sub 16}N{sub 2} is favored, whereas, in a ferrite matrix, Fe{sub 16}N{sub 2{minus}x} is favored. Further, in this article, methods are presented to calculate structure factors for nitrogen-deficient {alpha}{double_prime} and to obtain, from measured (=strained) lattice parameters, strain-free {alpha}{double_prime} lattice parameters from which the composition can be deduced.

• Sponsoring Organization: USDOE
• OSTI ID: 438584
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 1 Vol. 28; ISSN 1073-5623; ISSN MMTAEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
FERRITE
IRON ALLOYS
IRON NITRIDES
LATTICE PARAMETERS
MARTENSITE
MICROSTRUCTURE
NITRIDATION
PRECIPITATION
RECRYSTALLIZATION
ROLLING
SAMPLE PREPARATION
TEMPERING
VACANCIES
X-RAY DIFFRACTION