Why is fcc more ductile than bcc although bcc has greater number of slip planes than fcc?
See also - http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/deformation.htm
See figure 2a (fcc) and 2b (bcc) in the following. Note the angle between slip systems.
This may be the most helpful -
See page 134-135 of The Science and Engineering of Materials By Donald R. Askeland, Pradeep P. Fulay, Wendelin J. Wright
http://books.google.com/books?id=qz...4#v=onepage&q=Ductility slip fcc bcc&f=false
Alloying elements are by far more important than crystal lattice to determine ductility.
Take pure aluminium, it has virtually no limit to ductility. The sputtering targets I used got a notch by pressing one's nail on them.
But alloyed with 8% zinc (AA7049), aluminium loses much ductility, with only 8% guaranteed elongation at break.
One example of very ductile body-centred cubic is Armco iron:
It's used annealed and slowly cooled, ferritic (BCC), for its soft ferromagnetic properties, and also its resistance to corrosion.
Medium grades guarantee <0.01% of C, P, S and even Mn and Si. It's essentially plain ferritic pure iron.
With 200MPa yield strength, 40% elongation and 70% reduction of area at break, it is excellent at cold-forming. Such figures are absolutely similar to austenitic (FCC) iron-based alloys.
Hence my claim that essentially the alloying elements (C, P, S...) determine ductility.
P and S are generally considered impurities in most alloys, particularly structural materials. Both can increase notch sensitivity, or conversely reduce fracture toughness, particularly at cold temperatures.
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