Materials Science Flashcards
7 cards from real BME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Materials Science flashcards as text
Which corrosion type occurs when two dissimilar metals are in electrical contact in an electrolyte, causing the more active metal to corrode preferentially?
Answer: Galvanic corrosion
Galvanic corrosion occurs because the less noble (more active) metal becomes the anode and dissolves preferentially when coupled with a more noble metal in an electrolyte.
Superelastic behavior in shape memory alloys (e.g., Nitinol) is driven by:
Answer: Stress-induced martensitic phase transformation that is fully reversible
In superelastic alloys, applied stress induces a martensitic transformation; upon unloading, the martensite reverts to austenite, recovering all strain.
In Fick's second law of diffusion (∂C/∂t = D ∂²C/∂x²), what assumption is made about the diffusion coefficient D?
Answer: D is independent of concentration
Fick's second law in its standard form assumes D is constant (independent of concentration), simplifying the partial differential equation.
Which microstructural feature of cast iron gives gray iron its characteristic fracture appearance and machinability?
Answer: Flake graphite in a pearlitic matrix
Gray iron contains graphite flakes that act as stress concentrators, causing fracture along the flakes and producing the characteristic gray fracture surface.
The Weibull modulus (m) is used in ceramics to characterize:
Answer: The variability (scatter) in fracture strength
A high Weibull modulus indicates low scatter in fracture strength (reliable material), while a low modulus indicates high variability due to flaw distribution.
Which heat treatment process for steel involves austenitizing followed by quenching to a temperature above Ms and holding isothermally to form bainite?
Answer: Austempering
Austempering holds steel in the bainite transformation range isothermally, producing bainite with good toughness without the distortion risk of full quenching.
In a stress-strain curve for a ductile metal, the engineering stress decreases after the ultimate tensile strength (UTS) because:
Answer: Necking occurs and the cross-sectional area decreases faster than the load
After UTS, localized necking causes the cross-sectional area to decrease rapidly; although true stress continues rising, engineering stress (load/original area) drops.