Question

Explain why the deformation of a metal is energetically easier in some directions compared to others.

Answer 1

Pure metals are solids of a crystalline regular structure with some atomic packing.
In the bulk of any crystal, certain directions are not equivalent with respect to the location of atoms and distance between them. The plastic deformation begins from slipping of one part of the crystal framework with respect to the other in one of the possible crystallographical directions. These directions are energetically unequal, so the deformation of a metal will be easier on some of them. It is particularly true if the metal is a single crystal.