AIT Material Science 4 — Questions and Answers
Question 1: When selecting pipe material for a system carrying mildly corrosive chemicals, which material property is MOST important?
- Thermal conductivity
- Corrosion resistance (Correct answer)
- Tensile strength
- Magnetic permeability
Correct answer: Corrosion resistance
Corrosion resistance is the most critical property when selecting materials for systems handling corrosive substances.
Question 2: What is 'temper embrittlement' in alloy steels?
- Embrittlement caused by hydrogen absorption
- A loss of toughness after tempering in a specific temperature range (Correct answer)
- Cracking during the quenching process
- Softening of steel after prolonged high-temperature exposure
Correct answer: A loss of toughness after tempering in a specific temperature range
Temper embrittlement is the reduction in toughness of alloy steels tempered or slowly cooled through the 375–575°C range, caused by impurity segregation.
Question 3: Which non-destructive testing method uses high-frequency sound waves to detect internal flaws in materials?
- Magnetic particle testing
- Dye penetrant testing
- Ultrasonic testing (Correct answer)
- Visual inspection
Correct answer: Ultrasonic testing
Ultrasonic testing (UT) uses high-frequency sound waves to detect internal discontinuities and measure material thickness.
Question 4: What is the eutectic composition in a binary alloy system?
- The alloy with the highest melting point
- The composition that melts and solidifies at a single temperature lower than either pure component (Correct answer)
- The alloy with the best corrosion resistance
- The composition with the greatest ductility
Correct answer: The composition that melts and solidifies at a single temperature lower than either pure component
The eutectic composition is the specific alloy ratio that solidifies at the lowest possible temperature as a mixture of two phases simultaneously.
Question 5: Which type of polymer becomes soft and moldable when heated and hardens when cooled, repeatedly?
- Thermoset
- Elastomer
- Thermoplastic (Correct answer)
- Composite
Correct answer: Thermoplastic
Thermoplastics soften when heated and harden when cooled in a reversible process, allowing them to be remolded multiple times.
Question 6: In materials testing, what does 'yield strength' represent?
- The maximum stress a material can withstand before fracture
- The stress at which a material begins to deform permanently (Correct answer)
- The energy absorbed before fracture
- The ratio of stress to strain in the elastic region
Correct answer: The stress at which a material begins to deform permanently
Yield strength is the stress level at which a material transitions from elastic to plastic (permanent) deformation.
Question 7: What causes 'work hardening' (strain hardening) in metals?
- Heating the metal above its recrystallization temperature
- An increase in dislocation density due to plastic deformation (Correct answer)
- Adding alloying elements during manufacture
- Rapid cooling from high temperature
Correct answer: An increase in dislocation density due to plastic deformation
Work hardening occurs because plastic deformation increases dislocation density, and these dislocations impede each other's movement, making further deformation more difficult.
AIT Material Science 4
When selecting pipe material for a system carrying mildly corrosive chemicals, which material property is MOST important?