Question

Which of the following types of crystal are formed near the mould face during solidification?

(a) Big crystals with random orientation

(b) Small crystals with systematic orientation

(c) Small crystals with random orientation

(d) Big crystals with systematic orientation

I have been asked this question in homework.

My enquiry is from Mechanism of Solidification in chapter Cooling and Solidification of Casting-Forming-Welding I

Answer 1

Right option is (c) Small crystals with random orientation

Explanation: When a liquid metal is poured into a mould, the mould face itself acts as the nucleus for crystal growth, and when the conductivity of the mould is high, that causes the formations of randomly oriented small crystals which grow near the mould surface. Subsequently, a temperature gradient results within the casting.