NCEES Materials Science 5

Question 1

Creep in metals is most significant at temperatures above approximately what fraction of the absolute melting temperature (Tm)?

Accepted Answer

0.5 Tm

Answer

Significant creep deformation typically occurs above 0.4–0.5 Tm (absolute), where thermally activated diffusion and dislocation climb mechanisms become active.

Question 2

Which heat treatment process is used to increase the surface hardness of steel by diffusing carbon into the surface layer?

Accepted Answer

Carburizing

Answer

Carburizing exposes steel to a carbon-rich atmosphere at elevated temperature, allowing carbon to diffuse into the surface to create a hard, wear-resistant case.

Question 3

In the iron-carbon phase diagram, cementite (Fe₃C) contains approximately what weight percent carbon?

Accepted Answer

6.67 wt%

Answer

Cementite (iron carbide, Fe₃C) has a fixed stoichiometric composition of 6.67 wt% carbon, corresponding to 25 at% carbon.

Question 4

Which semiconductor doping type introduces extra electrons into the conduction band?

Accepted Answer

n-type doping

Answer

n-type doping introduces donor atoms (e.g., phosphorus in silicon) with extra valence electrons that become conduction electrons, increasing electron carrier concentration.

Question 5

The phenomenon where a material becomes magnetic below a specific temperature (Curie temperature) is called:

Accepted Answer

Ferromagnetism

Answer

Below the Curie temperature, magnetic domains in ferromagnetic materials align spontaneously due to quantum exchange interactions, producing strong net magnetization.

NCEES Practice Test

NCEES Practice Test

NCEES Materials Science 5