Research

Stacking-Fault Energies in Austenitic Steels

The stacking-fault energy (SFE) is a material property that affects the plastic deformation behavior. In the figure, the perfect fcc stacking ...ABCABCABC... is disturbed by the removal of a lattice plane C. An intrinsic stacking-fault is created with the new stacking ...ABCAB|ABCA... The energy needed to create such a defect is the SFE. A large SFE favours twinning-induced plasticity (TWIP) whereas a small SFE favors transformation-induced plasticity (TRIP). This means that under plastic deformation, austenitic TWIP steel promotes formation of twins whereas TRIP steel undergoes a martensitic fcc/hcp/bcc transformation. The latter leads to a pronounced increase of the ductility and strength of the austenitic TRIP steel.

The SFE of FeMn random alloys in the temperature range 300 - 800 K is being studied by means of ab-initio techniques. The DFT calculations are carried out using the exact muffin-tin orbitals (EMTO) method together with the coherent potential approximation (CPA) and the disordered local moment (DLM) approach to simulate the random alloy in the paramagnetic state. This work is part of the reasearch project Properties of Iron-based Alloys Investigated by Ab-initio Techniques.

People: Andrei Reyes Huamantinco, Peter Puschnig, Claudia Ambrosch-Draxl

Collaborations:
Andrei Ruban (Royal Institute of Technology, Stockholm, Sweden)
Manfred Wießner (Materials Center Leoben, Austria)
Jakob Wiener (University of Leoben, Austria)

Results:
A DFT-based methodology has been developed to calculate temperature-dependent stacking-fault energies. Temperature-dependent local magnetic moments are obtained through a longitudinal spin-fluctuation (LSF) Hamiltonian in combination with Monte Carlo simulations.

Publications:
[1] A. Reyes-Huamantinco, A. Ruban, P. Puschnig, and C. Ambrosch-Draxl (in preparation).