Formation Mechanisms of Alloying Element Nitrides in Recrystallized and Deformed Ferritic Fe-Cr-Al Alloy
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GASEOUS nitriding is one of the most widely employed thermochemical surface treatments to improve the mechanical (wear and fatigue) and chemical (corrosion) properties of ferritic steel components.[1] Gaseous nitriding is carried out in an NH3/H2 gas mixture. The atomic nitrogen from dissociating NH3 at the surface of the component gets incorporated into the surface of the specimen.[2–6] The inwardly diffusing nitrogen reacts with alloying elements dissolved in the matrix having affinity MARYAM AKHLAGHI, formerly Ph.D. Student with the Max Planck Institute for Intelligent Systems (formerly Max Planck Institute for Metals Research), Heisenbergstraße 3, 70569 Stuttgart, Germany, is now Research Scientist with the Institute of Iron and Steel Technology, Technische Universita¨t Bergakademie Freiberg, 09599 Freiberg, Germany. Contact e-mail: [email protected], [email protected] SAI RAMUDU MEKA, formerly Research Scientist with the Max Planck Institute for Intelligent Systems, is now Assistant Professor with the Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee, Roorkee, India. ERIC A. JA¨GLE, Group Leader, is with the Max-Planck-Institut fu¨r Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Du¨sseldorf, Germany. SILKE J.B. KURZ, formerly Research Scientist with the Max Planck Institute for Intelligent Systems, is now Analysis Engineer with Robert Bosch GmbH, Dieselstraße 6, 72770 Reutlingen, Germany. EWALD BISCHOFF, Research Scientist, is with the Max Planck Institute for Intelligent Systems. ERIC J. MITTEMEIJER, Director, is with the Max Planck Institute for Intelligent Systems and also Professor with the Institute for Materials Science, University of Stuttgart, Heisenbergstraße 3, 70569 Stuttgart, Germany Manuscript submitted November 24, 2015. Article published online July 8, 2016 4578—VOLUME 47A, SEPTEMBER 2016
for nitrogen (as Cr and Al) and forms alloying element nitrides.[7] Understanding the collective interaction of multiple alloying elements with nitrogen is a prerequisite for understanding the nitriding behavior of steels. It is generally recognized that the characteristics of the microstructure can decisively influence the mechanism of a precipitation process.[8] Thus, investigations on the recrystallized and cold-rolled specimens of binary Fe-Al[9,10] and Fe-Mo[11] alloys have revealed that the crystal lattice defects in cold-rolled specimens can lead to different nitride modifications and drastically influence the precipitation kinetics. Fundamental research on nitride precipitation processes until now has been largely devoted to recrystallized, i.e., more or less deformation-less, specimens and has focused on binary Fe-Me1 iron-based alloys: Fe-Cr,[12–16] Fe-Al,[10,17] Fe-V,[18,19] Fe-Ti,[20–22] and Fe-Si.[23–25] Only relatively few of such studies were devoted to recrystallized, ternary, iron-based Fe-Me1Me2 alloys, where two types of dissolved elements, Me1 and Me2, compete with each other in reacting with nitrogen.[26–37] In a number of cases, the surpri
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