1. Explain the difference
between ‘eutectic’ and ‘eutectoid’.
2. Explain the terms
‘hyper-‐ and hypoeutectoin ’and
‘hyper-‐ and hypoeutectic
An eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition made up of the same ingredients.
When the solution above the transformation point is solid, rather than liquid, an analogous eutectoid transformation can occur. For instance, in the iron-carbon system, the austenite phase can undergo a eutectoid transformation to produce ferrite and cementite, often in lamellar structures such as pearlite and bainite.
hypoeutectoid / Hypereutectoid (of steel)
having less/more carbon than the 0.8 percent of eutectoid steel.
Hypereutectoid
(of steel) having more carbon than the 0.8 percent ofeutectoid steel.
hypoeutectoid / Hypereutectoid of an alloy) having less/more of the alloying element than the eutectoid composition.
When the composition of an alloy places it to the right of the eutectic point it is called hyper-eutectic. Note, though, that this is merely convention. If the phase diagram had been drawn the other way around, with 100%A on the right and 100%B on the left, then the same alloy would be called hypo-eutectic, as it would be to the left of the eutectic point.
Is a chemical composition or temperature of a mixture of substances that gives the lowest temperature at which the mixture becomes fully molten.
1. The difference between 'eutectic' and 'eutectoid' lies in the composition and structure of the resulting phases in an alloy or mixture when it is cooled.
- Eutectic: In a eutectic system, two or more components combine to form a mixture that melts and solidifies at a specific temperature, known as the eutectic temperature. During cooling, the components solidify simultaneously, resulting in a microstructure of distinct phases. These phases can be identified under a microscope as individual solid solutions or compounds.
- Eutectoid: On the other hand, a eutectoid system involves a single component alloy or mixture that transforms into two different solid phases during cooling. This transformation occurs at a specific temperature, called the eutectoid temperature. The eutectoid reaction involves the simultaneous formation of two distinct solid phases throughout the material.
2. 'Hyper-' and 'hypo-eutectic' refer to the compositions of alloys or mixtures relative to the eutectic composition.
- Hypereutectic: A hypereutectic alloy or mixture contains a higher percentage of one or more components compared to the eutectic composition. For example, in a binary alloy system, if the eutectic composition is 70% A and 30% B, a hypereutectic alloy would have more than 70% A. This composition typically results in the formation of a eutectic mixture and excess of the primary phase during solidification.
- Hypoeutectic: A hypoeutectic alloy or mixture contains a lower percentage of one or more components compared to the eutectic composition. Continuing from the previous example, a hypoeutectic alloy would have less than 70% A. This composition usually leads to the formation of a eutectic mixture and excess of the secondary phase during solidification.
1. The difference between 'eutectic' and 'eutectoid' lies in their respective phase diagrams and the type of reactions that occur during solidification.
- Eutectic: A eutectic system refers to an alloy system that consists of two or more components that solidify from a liquid state into a mixture of two distinct phases at a specific composition and temperature. In a eutectic reaction, the liquid phase transforms directly into two solid phases simultaneously. This results in a fine microstructure composed of alternating layers or grains of different phases. The composition at which this occurs is known as the eutectic composition and the temperature at which it happens is called the eutectic temperature.
- Eutectoid: On the other hand, a eutectoid system involves an alloy system that consists of a single phase in the liquid state that transforms into two different solid phases upon cooling. In this case, the transformation occurs in a two-step process: first, the liquid phase solidifies into a primary solid phase, and then this primary solid phase undergoes a further transformation into two distinct solid phases. The composition at which the eutectoid reaction occurs is known as the eutectoid composition, and the temperature at which it happens is called the eutectoid temperature.
2. The terms 'hyper-eutectic' and 'hypoeutectic', as well as 'hyper-eutectoid' and 'hypoeutectoid', are used to describe the composition of an alloy in relation to the eutectic or eutectoid composition.
- Hyper-eutectic: This term refers to an alloy composition that has a higher concentration of one or more components than the eutectic composition. For example, in a hyper-eutectic alloy, there is a higher proportion of the component that forms the primary solid phase in a eutectic reaction.
- Hypoeutectic: Conversely, hypoeutectic denotes an alloy composition that has a lower concentration of one or more components than the eutectic composition. In a hypoeutectic alloy, there is a lower proportion of the component that forms the primary solid phase in a eutectic reaction.
- Hyper-eutectoid: When it comes to eutectoid systems, hyper-eutectoid refers to an alloy composition that has a higher concentration of the component that forms the eutectoid mixture of solid phases. This means that there is a higher proportion of the primary solid phase in the final microstructure.
- Hypoeutectoid: Finally, hypoeutectoid signifies an alloy composition that has a lower concentration of the component that forms the eutectoid mixture of solid phases. In a hypoeutectoid alloy, there is a lower proportion of the primary solid phase in the final microstructure.