Steel An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Iron Carbon

Most pure metals are soft and not very useful in their pure state. Are their any exceptions?

Therefore in order to increase desirable properties like strength, hardness and corrosion resistance we mix two or more pure metals together to give us an alloy.HardnessHSS Corrosion Resistance Stainless Steel StrengthBrass

Everyday examples of alloys include: 1. Bronze which is an alloy of Copper and Tin. Bronze is harder than pure copper. 2. Steel is an alloy of Iron and Carbon Steel is stronger than Iron. 3. Solder is an alloy of Tin and Lead.  Another example of course is aluminium alloy wheels.

ALLOYSALLOYS

When metals combine they sometimes become completely soluble in each other. Metals which combine in this way are said to form solid solutions.  When this type of alloy solidifies, only one type of crystal is formed.  Under a microscope the crystalline structure of a solid solution alloy looks very like a pure metal.

 Solid solution alloys have similar properties to pure metals but have greater strength.  They also have poorer electrical/thermal conductivity, greater hardness but not as elastic as pure metals.

Substitude AtomParent Atom Alloying Atom In Interstice Parent Atom Substitutional Solid Solution Alloys Interstitial Solid Solution Alloys

 Atoms of both metals are of similar size.  Direct substitution takes place.  Substitution normally at random. Substitude Atom Parent Atom SUPERLATTICE If substitution is ordered, it is called a SUPERLATTICE

NickelCopper

 Parent metal atoms are bigger than atoms of alloying metal.  Smaller atoms fit into spaces, (Interstices), between larger atoms. Alloying Atom In Interstice Parent Atom

Whereas many metals are ductile (literally, they can be drawn into wires) intermetallics tend to be brittle. For this reason pure intermetallics tend to be unattractive as engineering materials.

However they come into their own at high temperatures when they do become ductile. As a result some of the low density intermetallics, such as the titanium aluminides, are becoming attractive in a range of applications such as gas turbine blades (for jet aircraft and gas fired power stations)

Also for rapidly accelerating parts in internal combustion engines (such as rocker arms and turbo chargers).

The whole point of forcing the air/fuel mixture into an engine is to allow it to burn more fuel and make more power with the same engine capacity.

A turbocharger is used to force air/fuel mixture into an engine at a pressure greater then the natural atmospheric pressure of around 14.5 PSI.

The way a turbo works is the exhaust coming out of the engine is pushed through a turbine. Compressing the

For one thing when you compress air (with a turbo) it gets hotter. The problem with hotter air is that it contains less oxygen than cooler air, so there is less oxygen to help burn extra fuel that’s going into the engine

This is why many turbocharged cars use “intercooling” of various types, to cool the pressurised air back down into the engine.

Low density intermetallics are very usefull for high temterature and rapidly accelerating parts such as gas turbine blades, rocker arms and turbo chargers

These intermetallic compounds have higher melting point than either of the parent metal. This higher melting point indicates the high strength of the chemical bond in intermetallic compounds.

Intermetallics are compounds of two (or more) metallic elements that are held together by metal bonds. They show long range ordering, in other words they have a regularly repeating pattern. Compounds consist of a fixed ratio of atom. Intermetallic compounds are also know as “Intermediate Compounds” or “Intermediate Phases”

1. Compounds consist of a fixed ratio of atom, e.g. Nickel aluminide (Ni 3 Al) 2. Compounds show long range ordering, in other words they have a regularly repeating pattern. Intermetallics Standard Alloy

1. Electron Compounds 2. Interstitial Compounds

These compounds are very similar in structure to solid solutions. They take their name from the fact that compounds from according the valency electron ratio between the metals concerned.

An example of electron compound would be an alloy of the elements Magnesium and Tin which combine to form an intermetallic compound Mg 2 SN.  Metallic compounds form a crystal lattice with the atoms of the alloying metals taking up specific positions within the lattice. These compounds are usually hard and brittle. Mg 2 SN Magnesium 2 Atoms Tin 1 Atom

Interstitial compounds, as the name suggests form between metals, or metals and non- metallic elements, with atom sizes very similar to those that form interstitial solid solution. One set of atoms fit into the spaces, or interstices, between the larger atoms.

Iron Carbide (Fe 3 C) or CEMENTITE which is important in the study of Iron- Carbon diagrams is an example of an interstitial compound. What are the atoms are in a molecule of Cementite and how many of each are there? Fe 3 C Iron 3 Atoms Carbon 1 Atom

Iron 26 Carbon 6

Cu Al 2 is another example of an interstitial compound which is significant in AGE HARDENING aluminium alloys.