In a single crystal, the physical and mechanical properties often
differ with orientation. It can be seen from looking at our models
of crystalline structure that atoms should be able to slip over
one another or distort in relation to one another easier in some
directions than others. When the properties of a material vary
with different crystallographic orientations, the material is
said to be anisotropic.
Alternately, when the properties of a material are the same in
all directions, the material is said to be isotropic.
For many polycrystalline materials the grain orientations are
random before any working (deformation) of the material is done.
Therefore, even if the individual grains are anisotropic, the
property differences tend to average out and, overall, the material
is isotropic. When a material is formed, the grains are usually
distorted and elongated in one or more directions which makes
the material anisotropic. Material forming will be discussed later
but let’s continue discussing crystalline structure at the