Regensburg 2016 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 30: Structural Materials I

MM 30.2: Vortrag

Mittwoch, 9. März 2016, 10:30–10:45, H52

Atomic-scale modeling of point defects, phase stability, and the formation mechanism of Z phases CrMN (M=V, Nb, Ta) — •Daniel F. Urban, Matous Mrovec, and Christian Elsässer — Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg, Germany

The challenge of raising the steam inlet temperature of fossil-fired power plants calls for creep-resistant steels with a Cr content higher than 9% in order to achieve sufficient corrosion and oxidation resistance. However, it has been found that in 11-12% Cr ferritic-martensitic creep resistant steels strengthened by fine (V,Nb)N particles, precipitation of thermodynamically stable Z-phase particles, CrMN (M=V,Nb,Ta), in long-term service is unavoidable and detrimental. Usually, Z-phase particles are coarse and brittle and grow at the expense of the desired fine (V,Nb)N particles.

We present atomistic simulations, using density function theory, which reveal the essential mechanisms underlying the formation of Z-phases. We study the thermodynamic stability of Z-phase, related structures and predecessors as well as the basic phase formation mechanisms. The picture that evolves consists of the diffusion of Cr atoms into MN particles and their subsequent clustering in a layered arrangement which finally yields the transformation of the nitride particles to Z-phase particles. Our results support experimental efforts to control the precipitation of the Z-phase through appropriate microstructural engineering.