Experiment (2)
Effect of Solidification
Time on Microstructure
Introduction
Solidification Process: involves nucleation (homogeneous or heterogeneous),
crystal formation, growth followed by complete solidification by formation
of grains separated by grain boundaries Crystal formation and growth.
Latent Heat of Fusion: is the heat removed from the solid-liquid
interface before solidification is complete manner by which this heat is
removed determines the growth mechanism and final structure.
Planar Growth:When inoculation is good under equilibrium
conditions, the temp. of the liquid remains above the freezing temperature
and the solid temp. is at or below the freezing temp.
During solidification, the latent heat of fusion is removed from the S-L
interface to the surroundings and hence keeping the temperature of the
Liquid always higher than the freezing temperature any small protuberance
then stops until the remainder of the interface catches up.
Denderetic Growth: When nucleation is poor, the liquid undercools
before the solid forms, which results in a small solid protuberance called
dendrite forming at the interface followed by its growth.
As the solid dendrite grows, the latent heat of fusion is conducted into
the under-cooled liquid, hence raising the liquids’ temperature towards
the freezing temp.
Secondary and tertiary arms can form on the primary spikes.
Procedures
Using the same cast sections in experiment 1.
Knowing that the geometrical shapes cast in experiment 1, have different
V/A ratios, which varies the solidification time and hence affects the
produced microstructure, the current experiment should be conducted as
follows.
Cut specimens from each geometrical cast section, with dimensions that
are suitable for being held by fingers to carry on the grinding and polishing
steps.
a. Sectioning
b. Mounting
c. Course (planar) grinding gradually from rough to fine grinding
d. Rough polishing
e. Fine polishing
f. Etching
2. Investigate the effect of variation of solidification time on the
on the produced microstructure.
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