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

## Question:

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

## Miller Indices:

The notation of planes and directions in crystals are defined using Miller indices. The planes all including three numbers, which are Cartesian coordinates and are enclosed in either square brackets for one plane or curly brackets for a family of planes, for example [111] or {111}. A Miller index direction is written enclosed in two carets this this {eq}< 110> {/eq}.

## Answer and Explanation: 1

There are certain crystallographic planes called slip planes along which atoms can slide over each other more easily, In face-centered cubic (FCC) lattice, these slip planes are the close-packed planes, which are the {111} planes. There are a total of 12 slip systems in which slip is easiest in the FCC crystal. The {110} planes are the close-packed planes for the body-centered cubic (BCC) crystal and there are 6 total slip systems. The hexagonal closed-packed (HCP) lattice can only slip on the basal planes, so there are only 3 slip systems. This explains why deformation is easier in certain directions and why some metals are more ductile than others.

#### Learn more about this topic:

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Chapter 10 / Lesson 8Discover crystal lattice structures. Explore what a crystal lattice is, various types of crystal lattice structures and the concept of translational symmetry.