Which metals are stronger?

  • Thread starter jojoba
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"Which metals tend to be stronger, those that form FCC or those that form BCC crystals? "
This is the solution provided which doesn't make much sense to me: "You should look at APF and coordination number of each crystal system to base your answer"
Is this even a valid question? Doesn't the answer depend on which direction the material is going to be subjected to a force since "strongness" is a directional property? I thought we should choose a particular direction for both systems and look at planar and linear densities. Hence, the slip phenomenon in the crystal structure with a greater planar density in the "chosen direction" will progress with more ease which suggests that the the material is "stronger" if subjected to a force in the chosen direction.
I would appreciate it if someone could point me to the flaw in my reasoning.
It is a valid question. FCC metals tend to have more slip systems, i.e. slip directions and slip planes than BCC. Yes the APF is important, the atomic packing factor, that is the reason FCC has more slip systems, because of the way the atoms are arranged in the crystal.
Thus FCC metals deform easier than BCC metals and thus they are more ductile. BCC metals are infact stronger than FCC metals. HCP metals are the most brittle.
Calister or Smith explains this if you can get your hands on either of the books.

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