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Materials Science and Engineering Fundamentals
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Materials Science and Engineering Fundamentals
Materials Science and Engineering Fundamentals
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1
Question
What two interventions are recommended to alleviate stress corrosion cracking (SCC) in a metal sample?
Page 1
Answer
Removing the item from the corrodent and alleviating internal (residual) stresses through annealing.
2
Question
How is a steel containing 0.4 wt% carbon classified based on its carbon content relative to the eutectoid composition?
Page 1
Answer
It is classified as medium-carbon steel and hypoeutectoid steel.
3
Question
What are the primary microstructural constituents of a 0.4 wt% carbon steel after slow cooling to just below 700 °C?
Page 1
Answer
The microstructure consists of a mixture of ferrite (\(\\alpha\)-Fe) and pearlite.
4
Question
What are the major mechanical advantages of using medium-carbon steels compared to low or high-carbon variants?
Page 1
Answer
They offer a good strength–ductility balance, heat treatability, and better weldability/machinability than higher-carbon steels.
5
Question
How do hypoeutectoid steels and cast irons differ regarding their typical carbon content and fracture behavior?
Page 2
Answer
Steels have 0.4–0.6 wt% C and are tougher/less brittle, while cast irons have >2.1 wt% C and are more brittle.
6
Question
Which Non-Destructive Testing (NDT) method is most effective for detecting internal cracks and through-thickness flaws in welds?
Page 2
Answer
Ultrasonic Testing (UT) is highly effective for internal flaws by reflecting sound waves off discontinuities.
7
Question
In the context of shaped charge penetration, what formula is used to calculate the penetration depth (dL) based on density?
Page 3
Answer
\(dL = h\sqrt{\frac{\rho_t}{\rho_p}}\), where h is jet length, \(\rho_t\) is target density, and \(\rho_p\) is projectile density.
8
Question
Why are engineering ceramics generally brittle, and how do their atomic bonds contribute to this property?
Page 3
Answer
They have rigid ionic or covalent bonds that inhibit dislocation motion and atomic rearrangement without breaking.
9
Question
What are the common methods used to measure the elastic modulus and hardness of brittle ceramics?
Page 3
Answer
Elastic modulus is measured via ultrasonic testing or 3-point bending; hardness is measured using Vickers or Knoop tests.
10
Question
What is the distinction between stiffness and strength in metallic materials?
Page 3
Answer
Stiffness is resistance to elastic deformation (modulus), while strength is the maximum stress before plastic deformation or failure.
11
Question
What are the four main hardening mechanisms used to strengthen aluminium alloys?
Page 4
Answer
Solid solution strengthening, work (strain) hardening, grain refinement, and precipitation (age) hardening.
12
Question
What are the three key steps involved in the precipitation hardening (age hardening) heat treatment process?
Page 4
Answer
The steps are solution heat treatment, quenching, and ageing (natural or artificial).
13
Question
What structural and thermal characteristics distinguish amorphous solids from crystalline solids?
Page 5
Answer
Amorphous solids lack long-range order and have a glass transition range; crystalline solids have a regular lattice and a sharp melting point.
14
Question
Define the structure and formation of austenite (\(\\gamma\)-Fe) in the Fe-C system.
Page 6
Answer
Austenite is a Face-Centered Cubic (FCC) structure stable at high temperatures above the eutectoid temperature (727 °C).
15
Question
What are the characteristics and formation mechanism of martensite in steels?
Page 7
Answer
Martensite is a Body-Centered Tetragonal (BCT) structure formed by rapid quenching (diffusionless transformation) from austenite.
16
Question
Describe the tempering process and its effect on the mechanical properties of quenched martensite.
Page 7
Answer
Tempering involves reheating martensite to 150–600 °C to reduce brittleness and increase toughness/ductility.
17
Question
Why is hot working generally preferred over cold working for processing titanium alloys?
Page 7
Answer
It reduces flow stress, enhances plasticity, and enables dynamic recrystallization to refine grain size.
18
Question
How does grain refinement increase the yield strength of non-ferrous metals?
Page 8
Answer
Reducing grain size increases the number of grain boundaries, which serve as barriers to dislocation motion (Hall–Petch relationship).
19
Question
Explain the cause of high elastic modulus and high hardness in engineering ceramics based on atomic bonding.
Page 8
Answer
Strong interatomic forces (ionic or covalent) resist elastic deformation and displacement of atoms from lattice positions.
20
Question
What are the primary differences between natural and artificial aging for heat-treatable aluminium alloys?
Page 9
Answer
Natural aging occurs at room temperature over days; artificial aging occurs at elevated temperatures (100–200 °C) over hours and achieves higher strength.
21
Question
What is the main goal in welding hardenable steels to ensure mechanical integrity?
Page 9
Answer
Avoiding brittle phases like martensite in the heat-affected zone (HAZ) and preventing grain coarsening.
22
Question
Compare the microstructural and mechanical effects of forging/rolling versus Selective Laser Melting (SLM) for titanium alloys.
Page 11
Answer
Forging produces equiaxed/elongated grains (isotropic); SLM produces columnar grains and martensitic \(\alpha'\) (anisotropic, high strength, poor ductility).
23
Question
Identify the distinguishing phases and stabilizing elements for \(\alpha\) and \(\beta\) titanium alloys.
Page 11
Answer
\(\alpha\) alloys use Al, O, N (HCP structure); \(\beta\) alloys use Mo, V, Nb, Fe (BCC structure).
24
Question
What is the primary microstructural difference between annealed and normalized hypoeutectoid steels?
Page 7
Answer
Annealing produces coarse pearlite (furnace cooling); normalizing produces fine pearlite (air cooling).
25
Question
Define the chemical composition and mechanical properties of cementite (\(\text{Fe}_3\text{C}\)).
Page 6
Answer
Cementite is an orthorhombic intermetallic compound that is very hard and brittle, reducing ductility while increasing wear resistance.
26
Question
How does the cooling rate from the molten state influence the final structure of glass?
Page 5
Answer
Rapid cooling is required to prevent crystallization and maintain the disordered amorphous state.
27
Question
List four common welding techniques for steels and their typical applications.
Page 10
Answer
GTAW (precision/thin sections), GMAW (fast/versatile), SAW (thick plates), and LBW (low-distortion/high-value).
28
Question
What causes 'Hot Cracking' in welds, and what is its effect on joint integrity?
Page 10
Answer
It is caused by solidification shrinkage under tensile stress, resulting in fracture during cooling and reduced ductility.
29
Question
Why is 'Lack of Fusion' considered a critical flaw in a welded joint?
Page 10
Answer
It represents reduced bonding between the weld and base metal, acting as a major internal stress riser.
30
Question
What is the typical grain morphology found in the fusion zone (weld metal) of a steel weld?
Page 10
Answer
It usually exhibits columnar grains that grow from the fusion boundary toward the weld centerline.