The GATE Grind

GATE 2018 ME (ME2) – Question 22

Engineering Materials · Phase diagrams and heat treatment · 1 mark · Multiple choice

L denotes liquid and M solid; subscripts distinguish phases. A eutectoid reaction is ______.

  1. $M_1\to M_2+M_3$
  2. $L_1\to M_1+M_2$
  3. $L_1+M_1\to M_2$
  4. $M_1+M_2\to M_3$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) $M_1\to M_2+M_3$; (D) $M_1+M_2\to M_3$

Explanation

A eutectoid transformation decomposes one solid into two distinct solids, **M1→M2+M3, A**. Option D, M1+M2→M3, describes a peritectoid reaction. The official key nevertheless accepts **A OR D**; both grading alternatives are retained while the explanation distinguishes the physical definitions.