Coherency strain and precipitation kinetics: crystalline and amorphous nitride formation in ternary Fe-Ti/Cr/V-Si alloys

• Published in: Philosophical magazine (Abingdon, England) England), 2014-09, Vol.94 (27), p.3098-3119
• Main Authors: Schwarz, B., Rossi, P.J., Straßberger, L., Jörg, F., Meka, S.R., Bischoff, E., Schacherl, R.E., Mittemeijer, E.J.
• Format: Article
• Language: English
• Subjects: Alloys; Applied sciences; Coherence; coherency; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Ferrous alloys; Heat treatment; Materials science; Men; Metals. Metallurgy; misfit strain; Nanoscale materials and structures: fabrication and characterization; nitride-precipitation kinetics; Nitrides; nitriding; Other topics in nanoscale materials and structures; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitates; Precipitation; Production techniques; Silicon nitride; Surface treatments; ternary iron-based alloys; Thermochemical treatment and diffusion treatment
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786435.2014.952258

Specimens of iron-based binary Fe-Si alloy and ternary Fe-Me-Si alloys (with Me = Ti, Cr and V) were nitrided at 580 °C in a NH 3 /H 2 -gas mixture applying a nitriding potential of 0.1 atm −1/2 until nitrogen saturation in the specimens was attained. In contrast with recent observations in other Fe-Me 1 -Me 2 alloys, no "mixed" (Me 1 , Me 2 ) nitrides developed in Fe-Me-Si alloys upon nitriding: first, all Me precipitates as MeN; and thereafter, all Si precipitates as Si 3 N 4 . The MeN precipitates as crystalline, finely dispersed, nanosized platelets, obeying a Baker-Nutting orientation relationship (OR) with respect to the ferrite matrix. The Si 3 N 4 precipitates as cubically, amorphous particles; the incoherent (part of the) MeN/α-Fe interface acts as heterogeneous nucleation site for Si 3 N 4 . The Si 3 N 4 -precipitation rate was found to be strongly dependent on the degree of coherency of the first precipitating MeN. The different, even opposite, kinetic effects observed for the various Fe-Me-Si alloys could be ascribed to the different time dependences of the coherent → incoherent transitions of the MeN particles in the different Fe-Me-Si alloys.