Materials Science Flashcards

Which crystal defect involves an extra half-plane of atoms inserted into the crystal lattice?

Answer: Edge dislocation

An edge dislocation is characterized by an extra half-plane of atoms, creating a line defect that enables plastic deformation by slip.

The Hall-Petch relationship describes how yield strength varies with grain size. As grain size decreases, yield strength:

Answer: Increases

The Hall-Petch equation shows yield strength increases as grain size decreases because grain boundaries impede dislocation motion.

Which phase transformation occurs when austenite is rapidly quenched to form a body-centered tetragonal structure in steel?

Answer: Martensite formation

Rapid quenching of austenite traps carbon in the BCC iron lattice, distorting it into a BCT martensitic structure.

A material has a fracture toughness KIc = 50 MPa√m and a yield strength of 500 MPa. What is the critical crack length for plane strain fracture?

Answer: ~3.2 mm

Using a = (1/π)(KIc/σ)² = (1/π)(50/500)² ≈ 0.0032 m = 3.2 mm for a through crack with Y=1.

Which polymer chain configuration results in the highest degree of crystallinity?

Answer: Isotactic

Isotactic polymers have all substituents on the same side of the backbone, allowing chains to pack regularly into crystalline regions.

In a binary eutectic system, the eutectic point represents:

Answer: The composition and temperature where two solid phases and liquid coexist

At the eutectic point, the liquid phase transforms simultaneously into two distinct solid phases at a fixed composition and temperature.

Which strengthening mechanism involves introducing solute atoms that distort the crystal lattice and impede dislocation movement?

Answer: Solid solution strengthening

Solid solution strengthening occurs when solute atoms create local stress fields that interact with and pin dislocations.