Materials Science Flashcards

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

Answer: 0.5 Tm

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

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

Answer: Carburizing

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.

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

Answer: 6.67 wt%

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

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

Answer: n-type doping

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

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

Answer: Ferromagnetism

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

Which non-destructive testing (NDT) method uses high-frequency sound waves to detect internal flaws in materials?

Answer: Ultrasonic testing

Ultrasonic testing transmits high-frequency sound waves into a material and analyzes reflections to locate internal discontinuities, cracks, and voids.

Which phenomenon explains why ceramics are generally much weaker in tension than in compression?

Answer: Surface and internal microcracks propagate easily under tensile stress but close under compression

Pre-existing microcracks in ceramics act as stress concentrators under tension, promoting brittle fracture, while compressive loading closes these cracks rather than opening them.