LMS SEGi College*EAT104MANUFACTURING AND MATERIALS WEEK 3 THE
CRYSTAL STRUCTURE OF METAL
LMS SEGi College
From liquid to solid
A pure metal solidifies at a fixed single temperature, and the
atoms arrange themselves in some regular pattern.
Metal crystals
Miller IndicesPlane Indices
Direction indicesFigure: Direction indices for identifying
crystal directions, showing how the[166] direction is defined. The
lower part of the figure shows the family of (111) directions.
Dendritic solidificationWhen the temperature of a molten pure
metal falls below its freezing point, crystallisation will begin.
The nucleus of each crystal will be a single unit of the
appropriate crystal lattice. For example, in the case of a metal
with a body-centred cubic lattice, nine atoms will come together to
form a single unit and this will grow as further atoms join the
lattice structure.
Figure: The nucleus of a metallic crystal (inthis case a
body-centred cubic structure).
The early stages in the growth of a metallic dendrite.
The dendritic solidification of a metal
The influence of cooling rates on crystal sizeThe rate at which
a molten metal is cooling as it reaches the freezing temperature
affects the size of the crystals which form. Zones of different
crystal forms in an ingot.
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LMS SEGi College*ReferencesR.A. Higgins, 2006, Materials for
Engineers andTechnicians, 4th Editions, Butterworth-Heinemann.
