Why Are {111} Planes the Primary Slip Systems in Face Centered Cubic Metals?

[ws0619]

Hello,

Recently,I study about the slip systems of metals which regarding to the material science subject.
For face centered cubic(FCC),it slip system is {111}<110>.Hence the number of slip systems is 12.The{111}is the family for (111), (-111), (1-11), (11-1),(sorry！-1 means a bar line on top of 1).
From what I study about{111}which is the family,it not just containing those few crystallographic planes that I listed out on top,but why other planes are not consider as slip planes for FCC?

Thanks very much, I appreciate any insight.

 

[Mapes]

Slip can occur on other planes, but it's especially easy for a dislocation to move in the close-packed direction along a close-packed plane. For fcc crystals, this means {111}<110>. For bcc, it's {110}<111> (the close-packed direction on the closest-packed plane--there is no perfectly close-packed plane in bcc).