Materials Science Flashcards

During quenching, steel is rapidly cooled in order to:

Answer: Trap carbon in a supersaturated solid solution, forming hard martensite

Rapid quenching suppresses diffusion-controlled decomposition of austenite, trapping carbon and producing martensite — the hardest steel microstructure.

Martensite in steel is characterized by:

Answer: A hard body-centered tetragonal (BCT) structure formed by diffusionless transformation

Martensite forms via a shear (diffusionless) mechanism during rapid quenching, producing a BCT crystal structure that is extremely hard and brittle.

The lever rule in a binary phase diagram is used to determine:

Answer: The mass fractions of each phase in a two-phase region

The lever rule relates the overall composition to the phase compositions to calculate the relative mass fractions of each phase in a two-phase field.

The primary purpose of tempering quenched steel is to:

Answer: Reduce brittleness while retaining useful hardness

Tempering heats as-quenched martensite to a sub-critical temperature, allowing some carbon to precipitate and relieving residual stresses, thereby improving toughness.

Which class of polymers cannot be re-melted after initial setting because of their network structure?

Answer: Thermosets

Thermosets form irreversible, three-dimensional cross-linked covalent networks during curing, preventing them from melting upon reheating.

The primary strengthening mechanism in precipitation hardening (age hardening) is:

Answer: Fine coherent precipitates impeding dislocation motion

Age hardening works by forming fine, coherent precipitate particles that act as obstacles to dislocation movement, greatly increasing yield strength.

Compared to metals, ceramics are generally characterized by:

Answer: High hardness, brittleness, and low electrical conductivity

Ceramics are typically hard, brittle (low fracture toughness), electrically insulating, and have high melting points due to their ionic/covalent bonding.