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It's in a phase diagram topic. It's about $\ce{Cu}$-$\ce{Sn}$ phase diagram.

enter image description here And it has a question of:

Write the schematic diagram describing the following scenarios and identifies the regions and the phases when Slow cooling of $13.1\%$ $\ce{Sn}$ alloy from $\pu{1000^\circ C}$ to $\pu{300^\circ C}$ happens.

I have this schematic diagram that describes the following scenarios and identifies the regions and the phases at $40 \%\,\ce{Sn}$ alloy from $\pu{800 °C}$ "$\ce{L -> L}$ and $\ce{γ -> L}$, γ, and $\ce{ε -> L}$ and ε" as an example but it's confusing to follow. However, it's just an example and it doesn't follow the $\ce{Cu}-\ce{Sn}$ phase diagram anyway.

But does the first one mean $\ce{L -> L + γ}$?

And L , y are in different phases that manages to fall both at $40 \%\,\ce{Sn}$ alloy from $\pu{800 °C}?

Also am I correct to assume that the final one means $\ce{ε -> L + ε}$?

This is the closest image that I can give based on my assumption:

Development of microstructure in eutectic alloys (II)

At compositions between the room temperature solubility limit and the maximum solid solubility at the eutectic temperature, $\beta$ phase nucleates as the $\alpha$ solid solubility is exceeded upon crossing the solvus line enter image description here

[MSE 2009: Introduction to Materials Science; Chapter 9: Phase Diagrams; Page 28]

Here's the PDF file for more information.

"$\ce{L -> L}$ and $\ce{γ -> L}$, γ, and $\ce{ε -> L}$ and ε" is a schematic diagram for the slow cooling which means it is an equilibrium cooling Like this image given below:

Equilibrium Cooling in a $\ce{Cu-Ni}$ Binary System

Phase Diagram: $\ce{Cu-Ni}$ System.
System is:
--binary: i.e 2 components: $\ce{Cu}$ and $\ce{Ni}$.
--isomorphous: i.e., complete solubility of one component in another; a phase field extends from $0$ to $100\,\mathrm{wt}\%$
Consider $C_o = 35\,\mathrm{wt\%}$ $\ce{Ni}$

enter image description here

Another one is:

Ex: Cooling of $\ce{Cu-Ni}$ Alloy

Phase diagram: $\ce{Cu-Ni}$ system
Consider microstructural changes that accompany the cooling of a $C_o = \pu{35 wt\%}\, \ce{Ni}$ alloy enter image description here

Cored vs Equilibrium Structures

$C_o$ changes as we solidify

enter image description here

These images are from this PPT file.

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    $\begingroup$ No. The arrows (you could label each of them with a temperature) have the highest priority, over commas and "and", which are equivalent. Homework: go down starting from 40%/800°C and describe what will happen. (Below 415°C, a further phase appears, btw.) Remember: the unlabeled areas are forbidden, you cannot cross them. $\endgroup$
    – Karl
    Dec 29, 2020 at 10:07

1 Answer 1

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Consider the 40 at% (Sn) composition at 800 °C: it's a liquid.

When you cool it down at around 650 °C you enter a two-phase field: the solid gamma forms (Cu-enriched) and the liquid enriches in Sn. As you further cool down the gamma phase will continue to form, but with progressively higher content of Sn

You cool down at 640 °C and you enter a new different two-phase field: the liquid partially reacts with the gamma phase forming the solid epsilon phase. If you further cool down, the ε phase will continue to form from the liquid, but its composition will progressively enrich in Cu.

Just below 415 °C you enter into another two-phase field: the liquid will solidify into ε and η phase.

That's what occurs by cooling down to 300 °C, but if you further would cool down below 189 °C you will enter another two-phase field; in this case the ε and η' phases will form.

The amounts of the different phases at the different $T$ are obtained by applying the lever rule.

Take care, I described what happened from the thermodynamic point of view (that is what is represented in a phase diagram); the kinetics can remarkably change the things.

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