Level 1 — RecognitionMaterials Chemistry (Aerospace)

Materials Chemistry (Aerospace)

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Chapter: 5.4 Materials Chemistry (Aerospace) Level: 1 — Recognition (MCQ + Matching + True/False with justification) Time Limit: 20 minutes Total Marks: 30

Section A — Multiple Choice (1 mark each) — 10 marks

Choose the single best answer.

Q1. The principal strengthening alloying element in the 7075 aluminium alloy is: (a) Copper (b) Zinc (c) Magnesium (d) Silicon

Q2. The workhorse aerospace titanium alloy Ti-6Al-4V contains, by weight approximately: (a) 6% Al, 4% V (b) 6% V, 4% Al (c) 6% Al, 4% Mo (d) 6% Cr, 4% Ni

Q3. Which refractory metal has the highest melting point, making it favoured for rocket nozzle throats? (a) Molybdenum (b) Tantalum (c) Rhenium (d) Tungsten

Q4. Precipitation (age) hardening increases strength by: (a) Forming coarse grains that block slip (b) Forming a fine dispersion of second-phase precipitates that impede dislocation motion (c) Removing all alloying elements from solid solution (d) Increasing the density of the matrix by melting

Q5. The ceramic used for oxygen sensors and thermal barrier coatings due to its ionic conductivity and toughening (partial stabilisation) is: (a) Alumina (b) Silicon carbide (c) Zirconia (d) Silicon nitride

Q6. Reinforced Carbon-Carbon (RCC) was used on the Space Shuttle primarily for: (a) The crew cabin windows (b) The wing leading edges and nose cap (c) The main fuel tank insulation (d) The landing gear tyres

Q7. PICA (Phenolic-Impregnated Carbon Ablator) protects a spacecraft mainly by: (a) Reflecting all radiation away (b) Pyrolysis and sacrificial mass loss carrying heat away (c) Superconducting the heat to the interior (d) Melting and re-solidifying to seal cracks

Q8. Ultra-high-temperature ceramics (UHTCs) suited for sharp leading edges above 2000 °C include: (a) ZrB $_2$ and HfB $_2$ (b) SiO $_2$ and Al $_2$ O $_3$ (c) MgO and CaO (d) TiO $_2$ and Fe $_2$ O $_3$

Q9. Hydrogen embrittlement in high-strength steels is BEST described as: (a) Loss of ductility/toughness caused by atomic hydrogen diffusing into the lattice (b) Surface oxidation by water vapour (c) A form of thermal fatigue (d) Dissolution of the metal in acid

Q10. Anodising of aluminium alloys produces a protective layer of: (a) Aluminium nitride (b) Aluminium carbide (c) A thick aluminium oxide film (d) A copper plating

Section B — Matching (1 mark each) — 10 marks

Q11. Match each material/process in Column X to its correct role/description in Column Y. Write pairs (e.g., i–P).

Column X	Column Y
i. Inconel (Ni superalloy)	P. Sacrificial low-density ablator on Apollo command module
ii. AVCOAT	Q. Hot-section turbine components resisting creep/oxidation
iii. Silica tiles	R. Reusable thermal protection on Shuttle orbiter underside
iv. 2024 Al alloy	S. Aircraft fuselage skins (Cu-bearing, damage tolerant)
v. Tantalum	T. High-melting refractory liner for rocket nozzles

Q12. Match the heat-treatment process to its purpose. Write pairs.

Column X	Column Y
i. Annealing	P. Rapid cooling to trap a hard (e.g., martensitic) structure
ii. Quenching	Q. Slow cooling to soften, relieve stress, improve ductility
iii. Tempering	R. Air-cooling after austenitising to refine grain, uniform structure
iv. Normalising	S. Reheating a quenched part to reduce brittleness/regain toughness
v. Solution + ageing	T. Precipitation hardening sequence for Al/Ni alloys

Section C — True/False WITH Justification (2 marks each: 1 mark T/F, 1 mark justification) — 10 marks

Q13. "Silicon carbide (SiC) retains high strength and hardness at elevated temperatures and resists oxidation better than most metals." — True or False? Justify.

Q14. "Stress corrosion cracking requires only a corrosive environment and does not depend on mechanical stress." — True or False? Justify.

Q15. "In CFRP laminate lay-up, orienting all plies in the 0° direction gives equal strength in every in-plane direction." — True or False? Justify.

Q16. "Plasma spraying is a vapour-deposition technique carried out in a vacuum at room temperature." — True or False? Justify.

Q17. "Refractory metals such as tungsten and molybdenum are used bare (uncoated) in oxidising rocket exhaust because they resist oxidation excellently." — True or False? Justify.

Answer keyMark scheme & solutions

Section A (1 mark each)

Q1 — (b) Zinc. 7075 is an Al-Zn-Mg-Cu alloy; Zn (≈5.6%) is the primary strengthening element via η-phase (MgZn $_2$ ) precipitates. (1)

Q2 — (a) 6% Al, 4% V. By name and composition Ti-6Al-4V = 6 wt% aluminium (α-stabiliser), 4 wt% vanadium (β-stabiliser). (1)

Q3 — (d) Tungsten. W melts at ~3422 °C, the highest of listed metals, ideal for nozzle throats. (1)

Q4 — (b) Fine second-phase precipitates pin/impede dislocation glide, raising yield strength. (1)

Q5 — (c) Zirconia. ZrO $_2$ (yttria-partially-stabilised) provides transformation toughening and ionic (O²⁻) conduction; used in TBCs and O $_2$ sensors. (1)

Q6 — (b) Wing leading edges and nose cap experienced the highest re-entry temperatures; RCC handled them. (1)

Q7 — (b) Ablation: phenolic pyrolyses, char forms, and mass is lost, carrying heat away (sacrificial cooling). (1)

Q8 — (a) ZrB $_2$ and HfB $_2$ . Diboride UHTCs have melting points >3000 °C and are used for sharp hypersonic leading edges. (1)

Q9 — (a) Atomic H diffuses into the lattice, embrittling high-strength steel and causing delayed brittle fracture. (1)

Q10 — (c) Anodising grows a controlled thick Al $_2$ O $_3$ film improving corrosion/wear resistance. (1)

Section B (1 mark per correct pair)

Q11: i–Q, ii–P, iii–R, iv–S, v–T. (5 × 1)

Inconel → hot-section turbine parts (creep/oxidation resistance).
AVCOAT → Apollo low-density ablator.
Silica tiles → reusable Shuttle underside TPS.
2024 Al → Cu-bearing damage-tolerant fuselage skins.
Tantalum → high-melting refractory nozzle liner.

Q12: i–Q, ii–P, iii–S, iv–R, v–T. (5 × 1)

Annealing → slow cool, soften/relieve stress.
Quenching → rapid cool, trap hard structure.
Tempering → reheat quenched part, regain toughness.
Normalising → air-cool, refine grain.
Solution + ageing → precipitation hardening.

Section C (1 mark T/F + 1 mark justification)

Q13 — TRUE. (1) SiC is a covalent ceramic; it keeps high hardness/strength to >1400 °C and forms a protective SiO $_2$ passivating layer giving good oxidation resistance. (1)

Q14 — FALSE. (1) SCC needs the simultaneous action of a susceptible material, a specific corrosive environment, and a sustained tensile (mechanical) stress — remove any one and cracking is arrested. (1)

Q15 — FALSE. (1) All-0° plies are strong along the fibre direction but weak transversely; balanced multidirectional strength requires a lay-up such as $0/\pm45/90$ (quasi-isotropic). (1)

Q16 — FALSE. (1) Plasma spraying is a thermal-spray process using a very hot plasma jet (thousands of K) at/near atmospheric pressure; it is not a room-temperature vacuum vapour deposition. (1)

Q17 — FALSE. (1) W and Mo oxidise catastrophically in air/oxidising exhaust (MoO $_3$ volatilises, WO $_3$ forms) so they need protective coatings or are used in reducing/inert environments. (1)

[
  {"claim":"Q11 mapping i-Q,ii-P,iii-R,iv-S,v-T is the stored key",
   "code":"key={'i':'Q','ii':'P','iii':'R','iv':'S','v':'T'}; result = key=={'i':'Q','ii':'P','iii':'R','iv':'S','v':'T'}"},
  {"claim":"Q12 mapping i-Q,ii-P,iii-S,iv-R,v-T is the stored key",
   "code":"key={'i':'Q','ii':'P','iii':'S','iv':'R','v':'T'}; result = key=={'i':'Q','ii':'P','iii':'S','iv':'R','v':'T'}"},
  {"claim":"Total marks = 10 (SecA) + 10 (SecB) + 10 (SecC) = 30",
   "code":"result = (10*1)+(5+5)+(5*2)==30"},
  {"claim":"Ti-6Al-4V balance is titanium: 100-6-4 = 90 percent",
   "code":"result = 100-6-4==90"}
]