NCEES Materials Science 4

Question 1

Which microstructure forms when austenite is rapidly quenched to room temperature in steel?

Accepted Answer

Martensite

Answer

Rapid quenching prevents diffusion-controlled transformations, producing martensite—a hard, body-centered tetragonal phase formed by a diffusionless shear transformation.

Question 2

In fracture mechanics, the stress intensity factor K is related to applied stress σ, crack length a, and a geometry factor Y by:

Accepted Answer

K = Y σ √(πa)

Answer

The stress intensity factor is K = Yσ√(πa), where fracture occurs when K reaches the material's fracture toughness KIc.

Question 3

The addition of carbon to iron primarily increases hardness by:

Accepted Answer

Forming a solid solution that impedes dislocation motion

Answer

Carbon atoms occupy interstitial sites in iron, creating lattice strain fields that impede dislocation glide and increase strength and hardness.

Question 4

Which ceramic has the highest hardness and is widely used as an abrasive?

Accepted Answer

Diamond (C)

Answer

Diamond, with a Vickers hardness of ~10,000 HV, is the hardest known material and is extensively used as an industrial abrasive and cutting tool.

Question 5

Precipitation hardening (age hardening) of an alloy requires which sequence of heat treatments?

Accepted Answer

Solution treatment → quenching → aging

Answer

Precipitation hardening requires solution treatment to dissolve alloying elements, rapid quenching to create a supersaturated solid solution, then controlled aging to precipitate fine strengthening particles.

NCEES Practice Test

NCEES Practice Test

NCEES Materials Science 4