Stacking-fault energy

A stacking fault is a 2 -dimensional lattice defects in certain crystal structures. He in the face centered cubic crystal structure ( FCC) occurs, for example, which can be described as a stacking of the crystal planes with the sequence ... ABCABC. If this regularity is interrupted ( eg ABCBCABC ... ), then there is a stacking fault. Usually, this forms a local HCP lattice structure with the stacking ABAB ... from.

In general, stacking faults form most easily in the most densely packed crystal planes ( eg ( 111) in the FCC crystal), because in these the interaction between the atoms is strongest. Next they grow with the same argument most easily in the close-packed directions ( eg ( 112) in the FCC crystal).

The stacking fault is a significant lattice defect, since it results in the formation of grain boundaries, thus preventing the formation of single crystals. Stacking faults arise, for example through twinning or when a Partialversetzung running through the crystal. The smaller the stacking fault energy required for this purpose (SFE, stacking fault energy), the easier it forms a stacking fault.

Silver has a low SFE:

Therefore, dislocations can be easily split into partial dislocations. Screw dislocations have to constrict the cross slip under expenditure of energy, so the strength increases.

The splitting width continues to play an important role in the hot forming. Since split dislocations cross slip badly or can climb, in materials with low stacking fault energy, the dynamic crystal recovery is disabled, and there is a greater solidification of the metal instead. It may thus build up a sufficiently large driving force for dynamic recrystallization, which leads to a maximum force in the hot flow curve.

In pure iron, the SFE is:

For austenitic steels in some cases but

Therefore, only the latter show a TWIP effect.

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