How the nucleation is taking place in pure metals and alloys? Explain in brief.

Question-AnswerCategory: Mechanical EngineeringHow the nucleation is taking place in pure metals and alloys? Explain in brief.
Ashutosh Kumar asked 11 months ago

How the nucleation is taking place in pure metals and alloys? Explain in brief.

1 Answers
Mazurek Gravity answered 11 months ago

Alloys nucleate in the same manner as pure metals. However, during solidification, the liquid motion may break off dendrites and carry them into the liquid. Then the dendrites act as nuclei for more grains and multiply the number of grains that nucleate in the liquid.That would be a very difficult thing to do, if you mean “see directly”!
The nucleation and growth of second-phase particles (solidification in a liquid, precipitation of non-metallic or inter-metallic phases, etc) will take place either inside the body of the primary solute phase being studied, or on the surface of a container.
It is possible in some non-metallic physical systems to witness nucleation and growth, such as water crystal formation in vapor or onto a cold surface (on a window) etc, but that is probably not what you have in mind.
Other than mercury and gallium, most metals and their alloys have melting / solidification temperatures that require “robust” containment, and thus do not allow direct visual witnessing of their slow solidification.
One can pour them out onto an appropriate surface and chill them, but this will minimize the chance to see most macroscopic solidifcation phenomena, due to the high cooling rate. There are, however, some advanced techniques employed to examine the interior of very small laboratory containment vessels with X-rays, which can provide a kind of visual detection of the solidification dynamics of an alloy.Nucleation and Growth of Crystals ,
At the solidification temperature, atoms from the liquid, such as molten metal, begin to bond together and start to form crystals. The moment a crystal begins to grow is know as nucleus and the point where it occurs is the nucleation point.
When a metal begins to solidify, multiple crystals begin to grow in the liquid. The final sizes of the individual crystals depend on the number of nucleation points. The crystals increase in size by the a)Nucleation of crystals, b) crystal growth, c) progressive addition of atoms and irregular grains form as crystals grow grow until they impinge upon together, d) grain boundaries as seen in a adjacent growing crystal. microscope.

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