Question

Which of the following statements is true regarding phase equilibrium in a binary alloy system?

• A. The phase diagram of a binary alloy system typically includes solid, liquid and gas phases.
• B. At the eutectic composition in a binary alloy system, the system consists of a single phase.
• C. The liquid phase is always more stable than the solid phase in a binary system.
• D. The eutectic temperature is the lowest temperature at which the solid phase forms.

Hint:

Remember that the eutectic temperature marks the lowest point on a binary alloy phase diagram where the alloy begins to solidify.

Answer 1

The Correct Option is D

In a binary alloy system, the eutectic point is a specific composition and temperature where the liquid transforms into two solid phases simultaneously upon cooling.
The eutectic temperature is the lowest possible temperature at which the alloy remains in the liquid phase before solidifying.
Hence, at this temperature, the transition from the liquid to the solid phase occurs for the eutectic composition.
The other options are incorrect because:
- (1) A binary alloy phase diagram generally includes only solid and liquid phases, not gas.
- (2) At eutectic composition, two solid phases form, not one.
- (3) The stability of phases depends on temperature and composition; the liquid is not always more stable.
Therefore, the only correct and universally true statement is option (4).