Engineering

Homework 8

Part 1

1. Physically

2. Independently

3. 0.8

4. FCC

5. Supersaturated – body center tetragonal

6. Reheating

7. Cementite

8. Martensitic

9. iron carbide

10. carbon in the farm of graphite

11. carbon in the farm of graphite nodules

12. silicon

13. stoichiometric

14. heat- treatment procedure

15. non crystalline

16. 6

17. 4

18. inorganic

19. C60

20. a chemical bond

21. the simultaneous

22. uniformly

23. atomic diffusion

24. a glass

25. a hot

26. inorganic

27. non crystalline – viscous

28. a metal

Part 2

1.

Alloying element	Material properties	Applications
Silicon	• Good castability and high fluidity due to Al-Si eutectic • High corrosion resistance • Good weldability. • Low solidification shrinkage. • Machining difficulty in hypereutectic.	• Manufacturing of castings • Filler wires for fusion welding • Brazing of aluminum
Silicon + Copper	• Cu addition increases strength and machinability	• Automotive cylinder heads/blocks in place of cast iron. • Sand and permanent mould casting
Copper	• Strength and hardness at T up to 250oC is achieved from a combination of precipitation hardening together with dispersion hardening by intermetallic compounds. • Strength is higher than other cast Al alloys and comparable to wrought Al alloys.	• Aerospace housing • Flywheel housing
Magnesium	• High resistance to corrosion • Good machinability • Attractive anodized surface. • Little or no response to heat treatment.	• Chemical and sewage • Kitchen utensils

2. A

• Powdered ceramic material and a liquid mixed to prepare a stable suspension (slip).

• Slip is poured into porous mold and liquid portion is partially absorbed by mold.

• Layer of semi-hard material is formed against mold surface.

• Excess slip is poured out of cavity or cast as solid.

• The material in mold is allowed to dry and then fired.

3.

· Solution treating – alloy is first heated above the solvus temperature at 548 C and held until a homogeneous solid solution α is produced

· Quench – the alloy, which contains only in its structure, is rapidly cooled, or quenched. After the quench, the structure is a supersaturated solid solution αss. Diffusion less transformation.

· Age – the supersaturated α is heated at a temperature below the solvus temperature. At this aging temperature, atoms diffuse only short distances. α + θ phase formed

4.

· Alumina (Al2O3) is used to contain molten metal or in applications where a material must operate at high temperatures with high strength. Alumina is also used as a low dielectric constant substrate for electronic packaging that houses silicon chips. One classic application is insulators in spark plugs. Some unique applications are being found in dental and medical use. Chromium-doped alumina is used for making lasers. Fine particles of alumina are also used as catalyst supports.

· Diamond (C) is the hardest naturally occurring material. Industrial diamonds are used as abrasives for grinding and polishing. Diamond and diamond-like coatings prepared using chemical vapor deposition processes are used to make abrasion resistant coatings for many different applications (e.g., cutting tools). It is, of course, also used in jewelry.

· Silica (SiO2) is probably the most widely used ceramic material. Silica is an essential ingredient in glasses and many glass-ceramics. Silica-based materials are used in thermal insulation, refractories, abrasives, as fiber-reinforced composites, and laboratory glassware. In the form of long continuous fibers, silica is used to make optical fibers for communications. Powders made using fine particles of silica are used in tires, paints, and many other applications.

· Silicon carbide (SiC) provides outstanding oxidation resistance at temperatures even above the melting point of steel. SiC often is used as a coating for metals, carbon-carbon composites, and other ceramics to provide protection at these extreme temperatures. SiC is also used as an abrasive in grinding wheels and as particulate and fibrous reinforcement in both metal matrix and ceramic matrix composites. It is also used to make heating elements for furnaces. SiC is a semiconductor and is a very good candidate for high-temperature electronics.

Part 3

Alloying element	Material properties	Applications
Bronze	• Bronzes are generally about 10 percent heavier than steel • Bronzes are softer and weaker than steel	1. door and window frames 2. mail boxes and chutes
Brass	1-Highly malleable Acoustic properties 2- Corrosion resistance 3-Moderate-high mechanical 4-strength Substitutional solid 5-solution of copper and zinc	1- decoration for its bright gold-like appearance 2- for applications where low friction is required such as locks, gears, bearings, doorknobs, ammunition, and valves