Metals and Alloys Flashcards

Which crystal structure do most face-centered cubic (FCC) metals exhibit at room temperature?

Answer: FCC

Metals such as aluminum, copper, gold, silver, and nickel have an FCC crystal structure with atoms at cube corners and face centers.

The iron-carbon phase diagram shows that the maximum solubility of carbon in austenite (FCC iron) is approximately:

Answer: 2.14 wt%

Austenite can dissolve up to 2.14 wt% carbon at 1147 degrees C; beyond this, cementite (Fe3C) forms, and compositions above 2.14 wt% C are classified as cast irons.

The eutectoid composition in the iron-carbon system is approximately:

Answer: 0.77 wt% C

At 0.77 wt% C and 727 degrees C, austenite transforms to pearlite (alternating layers of ferrite and cementite) in the eutectoid reaction.

Age hardening (precipitation hardening) in aluminum alloys involves which sequence of steps?

Answer: Solution treatment, quenching, aging

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

Martensite in steel is formed by:

Answer: Rapid quenching that suppresses diffusional transformation

Martensite forms by a diffusionless, shear-type transformation when austenite is rapidly quenched, trapping carbon in a body-centered tetragonal structure.

Which alloying element is primarily added to steel to improve hardenability?

Answer: Chromium

Chromium significantly increases hardenability by shifting the TTT (time-temperature-transformation) curves to longer times, allowing martensite to form at slower cooling rates.