Metals study guide

Properties of mentals

Ductility, toughness, malleability, chemical resistance, tensile strength, electrical and thermal conductivity

Alloy

metal element combined with other elements

What defines a metal's properties?

atomic structure

Metal's structure

crystalline and large aggregations

Metal phases

refer to a homogeneous part of aggregation of material different from another part due to difference in crystal structure

Different molecular structures of metals

Simple cubic, face centered cubic, body centered cubic

Simple cubic

atoms are at corners of cube-shaped cell

Face centered cubic

gamma phase, atoms are at corners of cell with one atom at the center of each face (more dense)

Body centered cubic

alpha and delta phase, atoms are at corners of cell connected by one atom in the center of the cell (more ductile)

Basic methods of changing a metal's properties

work/strain hardening, thermal processing

Cold working processes

Rolling, Spinning, Peening, Bending, Pressing, Extruding

How does the orientation of the molecular structures play a major role in the product's properties?

orientation can either be preferred (anisotropy) or random (isotropy)

preferred orientation

material will have different properties in the direction of orientation versus other directions.

random orientation

the metal will have the same properties in all directions.

Why are metals not normally purified to 100%?

During the processing of metals, additional impurities are introduced unintentionally due to high cost involved in trying to eliminate impurities

Trade-offs of metals not being 100% purified

interstitial crystal structure and insolubility

What happens when an interstitial crystal structure is formed?

some atoms take up positions between the regular solvent atoms (the vacant spaces between lattice points)

Insolubility

Very few metals are insoluble in each other in the liquid phase (aluminum and lead would come closest to achieving insolubility).

Famous structures made from wrought iron

eiffel tower

Nucleation of metals

the process of adding a substance or using existing impurities to assist in growth of crystallites (dendritic or treelike) with a random distribution of crystallographic planes relative to one another.

Annealing

A heat treatment about 30C above the eutectoid temperature. Used to relieve stresses in the product so it makes the product softer. Material is cooled in the furnace, slowly, as the furnace cools

Normalizing

replaces full annealing because of time and cost constraints. Cooling is done in ambient air instead of the furnace. The end product will be slightly stronger and harder than a fully annealed product.

Quenching

Rapid cooling of a metal, the degree of cooling depends mostly on the quenching medium used. For drastic quenching, water or brine may be used, otherwise oil, molten salt baths , still air or molten sand may be used

What does quenching achieve?

greater strengths and hardness of the metal

Case hardening

Hardening the surface of a material through heating, inner layers are not overly affected.

Tempering

through controlled heating hardness can be drawn from the material (drawing)

Ferrous Metals - composition, characteristics and uses

Iron based metals that are prone to corrosion and magnetic at room temp

Non-Ferrous Metals - composition, characteristics and uses

Metals that don't contain iron that are non-magnetic, corrosion resistance, and good electrical and thermal conductivity

Common non-ferrous metals

aluminum, titanium, copper, nickel, magnesium

Work/strain hardening

used to change a metal alloy's structure to alter its properties by performing work (cold working) on the metal itself

Thermal processing

heating and cooling a metal to change its properties (annealing, grain refinement, quenching, case hardening, tempering)

Aggregation

collections of millions of crystals composed of different types of atoms held together by metallic bonds

Brass metallic composition

Copper, <50% zinc

Bronze metallic composition

copper, <10% tin

Monel metallic composition

nickel, copper

Hastelloy metallic composition

nickel, molybdenum, iron

Duranickel metallic composition

nickel, aluminum

Inconel metallic composition

nickel, chromium

Carbon content of cast iron

2-4%

carbon content of steel

<2%

if a metal has more carbon, it's..

more stiff