Metals and Metallic Alloys [4.2a]

Metals

Crystalline structures comprised of individual grains.

Grain Size

Influenced by the type of heat treatment a metal receives while it is cooling.

Large/Coarse Grains

• Slow cooling

• High tensile strength

• High toughness

• High ductility

• High malleability

Small Grains

• Rapid cooling (quench)

• Low tensile strength

• Low ductility

• Low toughness

• High brittleness

Alloys

A mixture that contains atleast one metal.

• Can be two metals - bronze (Cu+Sn)

• Metal and non metals - carbon steel (Fe+C)

Work Hardening

The process of toughening a metal through plastic deformation.

• when you twist a soft drink can back and forward and then it get gets stiff and then eventually fails

Tempering

A heat treatment process after work hardening. Increases toughness and ductility. Decreases hardness and brittleness.

Superalloys

Alloy that exhibits excellent mechanical strength, resistant to thermal creep deformation and has good surface stability.

Creep

Tendency of a metal to slowly deform due to long term exposure of stress, below the yield or ultimate strength. More severe when metals are subjected to melting point heat for long periods of time.

Oxidation Resistance

Ability of a material to resist the direct and indirect attack from oxygen and degradation.

Interaction between oxygen and different substances when they make contact, such as rust.

Ferrous Alloys

Contain iron, making them magnetic.

• Mild steel - carbon and iron (engineering purposes)

• Stainless steel - iron, nickel and chromium (cutlery and surgical instruments)

• Cast iron - carbon and iron - strong but brittle (to cover manholes)

Non-ferrous Alloys

Contains no iron.

• Aluminum - aluminium, copper and manganese - lightweight and easily worked (aircraft and soda cans)

• Copper (wiring and tubing bcs conducts heat/electricity)

• Brass - copper and zinc (ornamental purposes)

• Silver - mixing w copper makes sterling silver (jewelry)

• Lead (roofing, batteries and pipes)