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Deformation

Deformation mechanisms
Definition:Elementary physical processes comprising the deformation of the material – occuring as a single mechanism or in combination of different microstructural processes.
Explanation:In ultra clean steels, new approaches to improve matrix behaviour are investigated in order to enhance the local strain hardening in the vicinity of microcracks or local stress concentrations. This can be obtained by using different deformation phenomena; e.g. by transformation induced plasticity (→TRIP), by mechanically induced twinning that improves the local plasticity (→TWIP), or by a network of densely distributed local shear bands that are separated by a few nm, facilitating the dislocation movement or by microband formation (→MBIP). These concepts are based on the assumption that an increase in local strain hardening compensates a possible local microstructural degradation.

The main requirement for the activation of supportive deformation mechanisms for dislocation gliding is a low stacking fault energy (→SFE) value. Both TWIP and TRIP mechanisms (mechanical twinning and ε-martensite formation) are related to the dissociation of perfect dislocations into Shockley partials, and thus, are related to the energy of the created stacking faults (→SFs). The crystallographic changes associated with the formation of a twin or ε-martensite plate are explained in terms of the arrangement of SFs: identical Shockley partial dislocations are packed on every close-packed {111} plane for a twin and on every second close-packed {111} plane for ε-martensite. Therefore, the active plasticity mode is directly related to the SFE.
SFB-Link:Refers to all projects that are concerned with the plastic deformation of steels.
References:Bleck, W.: ASIA Steel 2012 proceedings