Phases present in the system

Summary

The video script discusses the use of phase diagrams to determine the phases present in a material at a specific composition and temperature. Focusing on the binary copper-nickel phase diagram, it explains how to identify single and two-phase regions. The script introduces the 'one-to-one rule,' which states that between regions of single phases in a binary phase diagram, there must be a two-phase region. This rule helps in understanding phase diagrams, particularly when two-phase regions are not explicitly labeled.

Takeaways

• 📊 A phase diagram can answer three main questions: identifying phases present at a given composition and temperature, determining the types of phase transitions, and understanding the phase behavior as a function of composition and temperature.
• 🔍 The x-coordinate on a phase diagram represents composition, while the y-coordinate represents temperature, which are crucial for pinpointing the phases in equilibrium at a specific point.
• 🌡️ By examining the phase diagram, one can easily determine the phase(s) present at a given composition and temperature by locating the corresponding point on the diagram.
• 🛠️ The binary copper-nickel phase diagram is used as an example to illustrate how to read and interpret phase diagrams, highlighting the regions for liquid phase, solid solution (alpha phase), and two-phase regions.
• 📌 Point A in the script, with 60 weight percent nickel and 1200 degrees Celsius, falls within the alpha phase region, indicating that the alloy at this point is in the alpha phase.
• 🔬 Alloy B, with 50 weight percent nickel and 1250 degrees Celsius, is located in the two-phase region, suggesting the presence of both alpha and liquid phases in the alloy at this temperature and composition.
• 🔄 The 'one-to-one rule' in binary phase diagrams states that if you move horizontally across a phase boundary from one single phase to another, there will always be a two-phase region in between.
• 📚 In many standard phase diagrams, single-phase regions are often listed, and the two-phase regions can be inferred as combinations of those single-phase regions, making the one-to-one rule a useful tool for interpretation.
• 🔍 The script emphasizes the importance of understanding phase diagrams for materials scientists and engineers, as they provide a visual representation of phase equilibria and can guide in the selection of processing conditions for materials.
• ⚖️ In binary alloys, specifying the weight percent of one component is sufficient to define the composition, as the other component's percentage can be calculated by subtracting from 100%.

Q & A

What is the primary purpose of a phase diagram?

A phase diagram is used to determine the phases present at a given composition and temperature, showing the equilibrium conditions of different phases in a binary alloy system.

How does the x-coordinate in a phase diagram represent composition?

In a phase diagram, the x-coordinate represents the composition, typically in terms of weight percent of one of the alloying elements.

What does the y-coordinate in a phase diagram signify?

The y-coordinate in a phase diagram signifies temperature, which is a critical factor in determining the phases present in an alloy.

What is the significance of the alpha phase in the context of the binary copper-nickel diagram?

In the binary copper-nickel diagram, the alpha phase represents a solid solution phase where nickel is dissolved in copper, existing within a certain composition and temperature range.

What does the liquid phase region in a phase diagram indicate?

The liquid phase region in a phase diagram indicates the temperatures and compositions at which the alloy is entirely in a liquid state.

What is meant by a 'two-phase region' in a phase diagram?

A 'two-phase region' in a phase diagram is an area where two different phases coexist in equilibrium at a given temperature and composition.

How can you determine the phases present in an alloy at a specific temperature using a phase diagram?

To determine the phases present in an alloy at a specific temperature, plot the alloy's composition on the x-axis and the temperature on the y-axis, then observe which phase region the plotted point falls into.

What is the 'one to one rule' in binary phase diagrams?

The 'one to one rule' in binary phase diagrams states that if you move horizontally across a phase boundary from one single phase to another, there will always be a two-phase region in between.

Why might some phase diagrams only show single-phase regions?

Some phase diagrams may only show single-phase regions because the two-phase regions can always be deduced as the combination of those single-phase regions, making the explicit labeling of two-phase regions unnecessary.

What happens when an alloy's composition and temperature correspond to a point in the two-phase region of a phase diagram?

When an alloy's composition and temperature correspond to a point in the two-phase region of a phase diagram, the alloy will consist of a mixture of the two phases that are indicated by the boundaries of that region.

How does the phase diagram help in understanding the equilibrium state of an alloy?

The phase diagram helps in understanding the equilibrium state of an alloy by providing a visual representation of the conditions under which different phases are stable, allowing one to predict the phases present at any given composition and temperature.

Outlines

00:00

🔍 Understanding Phase Diagrams

The paragraph discusses the utility of phase diagrams in identifying the phases present at a specific composition and temperature. It uses the binary copper-nickel phase diagram as an example, explaining that the x-coordinate represents composition (in this case, weight percent of nickel) and the y-coordinate represents temperature. The paragraph illustrates how to determine the phase of an alloy by its position on the diagram. For instance, an alloy with 60 weight percent nickel at 1200 degrees Celsius falls within the alpha phase region, indicating it is in the alpha phase. Another example is an alloy with 50 weight percent nickel at 1250 degrees Celsius, which is in a two-phase region, suggesting the presence of both alpha and liquid phases. The paragraph emphasizes the simplicity of reading phase diagrams to ascertain equilibrium phases.

05:06

📏 The One-to-One Rule in Phase Diagrams

This paragraph delves into a fundamental rule in binary phase diagrams known as the one-to-one rule. It explains that when moving horizontally across a phase diagram (along an isotherm), if one starts and ends with single phases (e.g., liquid and alpha), there will always be a two-phase region (liquid plus alpha) in between. This rule is not commonly found in literature but is crucial for understanding phase diagrams. The paragraph clarifies that many standard phase diagrams may only list single-phase regions, implying that the two-phase regions can be deduced as combinations of those single-phase regions. This is particularly helpful when phase diagrams do not explicitly label two-phase regions, allowing users to predict their presence using the one-to-one rule.

Keywords

💡Phase Diagram

A phase diagram is a graphical representation of the conditions under which different phases of a material coexist in thermodynamic equilibrium. It is a crucial tool in material science and engineering, as it helps predict the phases present in a system at a given temperature and composition. In the video, the phase diagram is used to determine the phases present in a copper-nickel alloy at specific temperatures and compositions, illustrating its fundamental role in understanding material properties.

💡Binary Alloy

A binary alloy is an alloy composed of two elements. The script specifically discusses a copper-nickel binary alloy, highlighting that the composition can be defined by the percentage of one element, as the other is inferred. Binary alloys are simpler systems to study, as they involve fewer variables compared to multi-component alloys, and they are used to demonstrate basic principles of phase diagrams.

💡Phases

Phases refer to the distinct states of matter in a system, such as solid, liquid, or gas, that coexist in thermodynamic equilibrium. The video explains how a phase diagram can be used to identify the phases present at a given point, such as the alpha phase or a mixture of liquid and alpha phases in a copper-nickel alloy, depending on the temperature and composition.

💡Equilibrium

Equilibrium in the context of the video refers to the state where the phases of a material are stable and no further changes occur when the system is undisturbed. The script uses the concept of equilibrium to explain that when an alloy is heated to a certain temperature and held there long enough, the phases present will be in equilibrium, as depicted on the phase diagram.

💡Composition

Composition in the script refers to the proportion of elements in an alloy, typically expressed as weight percent. It is a key variable on the x-axis of the phase diagram and is essential for determining the phases present at a given temperature. The video uses the composition to locate points on the diagram and predict the phases in an alloy, such as 60 weight percent nickel.

💡Temperature

Temperature is another critical variable in phase diagrams, represented on the y-axis. It is used alongside composition to pinpoint the phase or phases that are in equilibrium at a given condition. The video discusses how different temperatures, such as 1200 degrees Celsius or 1250 degrees Celsius, correspond to different phases or combinations of phases in a copper-nickel alloy.

💡Alpha Phase

The alpha phase mentioned in the script is a specific solid solution phase in the copper-nickel system. It is one of the regions on the phase diagram where a single phase exists. The video explains that if a point falls within the alpha region, the alloy is in the alpha phase, which is a key outcome from analyzing the phase diagram.

💡Liquid Phase

The liquid phase in the script refers to the region on the phase diagram where the alloy is entirely in the liquid state. This is one of the single-phase regions that can be identified on the diagram. The video uses the liquid phase to illustrate how the phase of an alloy changes with temperature and composition, such as being in the liquid phase at high temperatures.

💡Two-Phase Region

A two-phase region on a phase diagram indicates a temperature and composition range where two different phases coexist in equilibrium. The script uses the example of a 50-50 alloy at 1250 degrees Celsius, which falls into a two-phase region, indicating the presence of both liquid and alpha phases. This concept is crucial for understanding the microstructure and properties of alloys.

💡One-to-One Rule

The one-to-one rule discussed in the script is a principle that helps predict the presence of two-phase regions in a binary phase diagram. It states that if you move horizontally across a phase boundary from one single phase to another, there will always be a two-phase region in between. This rule is illustrated in the video by showing that between the liquid and alpha phases, there is a region where both phases coexist.

Highlights

Phase diagrams can answer three fundamental questions about materials.

The first question a phase diagram addresses is identifying the phases present at a given composition and temperature.

The x-coordinate on a phase diagram represents composition, while the y-coordinate represents temperature.

The binary copper-nickel phase diagram is used as an example to explain phase identification.

In the binary copper-nickel diagram, different regions represent liquid phase, solid solution phase (alpha), and a two-phase region.

Point A on the diagram represents an alloy with 60 weight percent nickel at 1200 degrees Celsius, which is in the alpha phase.

In a binary alloy, specifying one component's weight percent is sufficient to define the composition.

Point B represents an alloy with 50 weight percent nickel at 1250 degrees Celsius, which is in a two-phase region with both alpha and liquid phases.

The one-to-one rule in binary phase diagrams states that moving horizontally across a phase boundary from one single phase to another will always include a two-phase region in between.

Phase diagrams can be used to determine the phases present in an alloy at equilibrium by plotting the point of interest.

The presence of two-phase regions in phase diagrams can often be deduced without explicit labeling, following the one-to-one rule.

Phase diagrams are essential tools for understanding and predicting material properties and behavior.

The binary copper-nickel phase diagram is a familiar example used to teach the basics of phase diagrams.

Understanding phase diagrams is crucial for material scientists and engineers to design alloys with desired properties.

The convention in binary alloys is to express composition in terms of one component's weight percent, with the other component being implicitly defined.

The phase diagram's ability to answer questions about material phases is a fundamental aspect of materials science.

The one-to-one rule simplifies the interpretation of phase diagrams, especially when two-phase regions are not explicitly marked.

Transcripts

So, as we saw we had three questions which a phase diagram can answer and we are now

going to take up these questions one by one.

The first question is what are the phases present at a given point in the phase diagram

at a given composition remember the x coordinate is composition and the y coordinate is temperature.

So, at a given composition and temperature what are the phase is in equilibrium.

This is a very important and a very direct question and can be answered very very simply

by just looking at the phase diagram . So, remember we come to our familiar binary

copper nickel diagram . So, binary copper, nickel diagram you we have been using.

In fact, we have introduced only this phase diagram as yet .

So, you are quite familiar with this now, binary copper nickel diagram and we saw that

this region is the liquid phase, this region is a solid solution phase which we call alpha

and this region is a two phase region.

Then depending on where my constitution point is.

So, for example, if I if I look at let us say this point . So, this point is let me

call this point A . So, point A first of all if I look at its x component that is 60 weight

percent nickel.

So, this means it is an alloy of 60 weight percent nickel and if I look at the y coordinate

it is 1200 degrees celsius . So, a 60 weight percent nickel alloy and I am only writing

60 weight percent nickel because we have binary alloy.

So, this is the convention in binary alloy since the other component; obviously, will

be 100 minus the component which you have given.

So, for example, 60 weight percent nickel automatically means that it is 40 weight percent

copper.

So, if you service you can write , but giving one component the proportion of one component

it is sufficient to define the composition for binary alloy . So, we have 60 weight sorry

6 40 weight percent copper . So, 60 weight percent nickel 40weight percent copper.

Either of them you can give, but we since we are saying that we are using weight percent

nickel as our composition axis.

So, we we will give 60 weight percent nickel as the composition of this alloy.

So, this is my point and the alloy has been equilibrated at 1200 degree celsius.

So, the question what is the phase here?

All you have to do is to see in which region it is falling.

Since it is falling in the alpha region we will say that this is an alpha phase phases

alpha phase . Now, let us look at another another alloy

just look at this one alloy B or constitution point B . So, if we

now look at its x component that is 50.

So, the composition is 50 weight percent nickel there is a 50 50 alloy and if I look at the

temperature I find that it is 1250 degrees celsius.

So, an alloy of 50 weight percent nickel, 50 weight percent copper is being headed at

1250 degrees celsius.

So, what are the phases present?

So, this time we get get a little bit more interesting answer because now it is falling

in the two phase region.

So, we will find that two phases are present in this alloy.

So, both alpha and liquid are present at this point.

So, at this point if I take such an alloy and heat it to 1250 degrees celsius and hold

it in equilibrium at; that means, I wait for long enough time for equilibrium to be achieved

then I will find that alloy is a mixture of two phase two phases

So, this is a two phase structure, this is the basic function of a phase diagram and

this is something which phase diagram can very easily answer you just have to look at.

But plot the point of your interest on the phase diagram and read the phases present.

An interesting thing which happens when you, let me draw the boundaries an interesting

thing which happens when you look at a phase diagram .

If we have only looked at this phase diagram as yet, but you must notice that if I am dead

on on the left hand side is the liquid phase on the right hand side is alpha phase and

in between liquid plus alpha phase is there this is not by accident, but this is always

going to be true in a binary phase diagram.

So, we write it as a rule.

So, that is if I if I cross phase boundaries across a horizontal line such that at one

end I have a given phase and at another end I have another single phase at one end I have

one single phase that is what this one means that I have a one single phage in this case

liquid.

At another end I have another single phase alpha, then in between there has to be a region

where mixture of these two phases should be present.

So, liquid plus alpha.

So, this is always true in a binary phase diagram and we call this with a name one to

one rule always this name is very not very common in literature, but we will be using

in this course . So, let me write this down.

If we move horizontally means a since our y axis is temperature moving horizontally

is moving along an isotherm . So, if we are moving along an isotherm from

one single phase one single phase in this case let us say example liquid two to another

single phase in this example alpha .

This is for example, it can be any phage example liquid example alpha, then we will always

have a 2 phase liquid plus alpha region whatever that single phases were there . So, if one

phase was alpha another phase was beta then the two phase alpha plus beta will be present.

So, we will always have a two phase region in between.

So, this is important and in fact, many standard phase diagrams which you will come across

in the literature many times they will list only the single phase region because the two

phase regions always can be found as the combination of those two single phase regions.

So, sometimes you will find in the phase diagram that the two phase regions are not labeled.

So, this one to one rule is helpful from that point of view