ME Corrosion and Degradation 2

Question 1

Stress corrosion cracking (SCC) requires the simultaneous presence of:

Accepted Answer

A susceptible material, a specific corrosive environment, and tensile stress

Answer

SCC occurs only when all three conditions are simultaneously met: a susceptible alloy, a specific corrosive environment (e.g., chlorides for austenitic stainless steel), and sustained tensile stress.

Question 2

Hydrogen embrittlement in high-strength steels is caused by:

Accepted Answer

Atomic hydrogen diffusing into the lattice and reducing ductility and toughness

Answer

Atomic hydrogen absorbed from electroplating, welding, or corrosion diffuses interstitially into steel, accumulating at stress concentrations and causing premature brittle fracture.

Question 3

Cavitation erosion occurs in hydraulic components when:

Accepted Answer

Vapor bubbles form and collapse violently near the surface, causing pitting

Answer

Cavitation creates vapor bubbles in low-pressure zones; when they collapse near a metal surface, micro-jets impact the surface with enormous pressure, causing pitting and material loss.

Question 4

The Evans diagram (mixed potential theory) predicts the corrosion potential and corrosion current by finding:

Accepted Answer

The intersection of the anodic and cathodic polarization curves

Answer

At the mixed potential (corrosion potential), the total anodic oxidation current equals the total cathodic reduction current; this intersection on the Evans diagram gives the corrosion potential and rate.

Question 5

Crevice corrosion occurs in tight gaps (under fasteners, gaskets) because:

Accepted Answer

Oxygen depletion inside the crevice creates an anodic region relative to the outside surface

Answer

Inside a crevice, oxygen is consumed and not replenished, creating a differential aeration cell where the oxygen-depleted interior becomes anodic and actively corrodes.

ME - Materials Engineer Practice Test

ME - Materials Engineer Practice Test

ME Corrosion and Degradation 2