Nitriding response of ferritic Fe-Ti-Cr alloys*

K. S. Jung; R. E. Schacherl; E. Bischoff; E. J. Mittemeijer

doi:10.3139/105.110072

Article

Nitriding response of ferritic Fe-Ti-Cr alloys*

K. S. Jung , R. E. Schacherl , E. Bischoff and E. J. Mittemeijer

Published/Copyright: May 31, 2013

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From the journal HTM Journal of Heat Treatment and Materials Volume 65 Issue 5

Abstract

Specimens of ferritic iron-based Fe-Ti-Cr alloys, containing a total of 0.30 at.% alloying elements, Ti and Cr with varying Ti/Cr atomic ratio (0.45, 0.87 and 1.90), were nitrided in a NH₃/H₂ gas atmosphere at 580 °C. The microstructure of the nitrided zone was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nitride platelets (length ≤ 30 nm and thickness ≤ 1 nm) developed in the nitrided zone. Particularly clear for the larger Ti/Cr atomic ratios, a tetragonally distorted ferrite develops next to the cubic ferrite, as evidenced both by XRD and TEM. The absence of separate TiN and CrN diffraction spots in the selected area electron diffraction patterns suggests the development of mixed Ti_xCr_1-xN nitride precipitates. The mixed Ti_xCr_1-xN nitride precipitates are of rock-salt crystal structure type and obey a Bain orientation relationship with the ferrite matrix.

Kurzfassung

Ferritische Fe-Ti-Cr-Legierungen, welche insgesamt 0,3 at.% der Legierungselemente Ti und Cr enthielten, jedoch mit unterschiedlichen atomaren Ti/Cr-Verhältnissen (0,45; 0,87 und 1,90), wurden in einer NH₃/H₂-Gasatmosphäre bei 580 °C nitriert. Die Mikrostruktur der nitrierten Zone wurde mit Röntgenbeugung und Transmissionselektronenmikroskopie (TEM) untersucht. Plättchenförmige Nitride (Länge ≤ 30 nm und Dicke ≤ 1 nm) bildeten sich in der nitrierten Zone. Besonders deutlich bei den größeren atomaren Ti/Cr-Verhältnissen wurde die kubische Ferritmatrix teilweise tetragonal verzerrt, wie mit Röntgen- und Elektronenbeugung (TEM) nachgewiesen wurde. Das Fehlen separater TiN- und CrN- Beugungsreflexe in den Feinbereichsbeugungsbildern lässt auf die Bildung von gemischten Ti_xCr_1-xN-Nitridausscheidungen schließen. Diese haben eine kubische Kristallstruktur vom NaCl-Typ und eine Bain'sche Orientierungsbeziehung zur ferritischen Matrix.

Keywords: gas nitriding; nitride precipitation; ternary alloy; mixed nitride

Schlüsselwörter: Gasnitrieren; Nitridausscheidung; ternäre Legierungen; Mischnitride

Lecture hold by K. S. Jung at the European Conference on Heat Treatment 2010, Nitriding and Nitrocarburising, April 29/30, 2010, Aachen, Germany.

§k.s.jung@mf.mpg.de

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Published Online: 2013-05-31

Published in Print: 2010-10-01

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https://doi.org/10.3139/105.110072

Keywords for this article

gas nitriding; nitride precipitation; ternary alloy; mixed nitride