Alloy

Binary alloying

Binary alloying with only one phase

A homogeneous alloy consists of only one homogeneous phase solid. To obtain a homogeneous alloy, it is necessary that there is total miscibility between the alloy elements. There are two possibilities:

* the two alloy elements are soluble one in another whatever their respective proportions.

*la concentration of the alloy element is lower than the limit of solubility.

Conditions to obtain a homogeneous alloy with total solubility in a solid state (rule of Hume-Rothery):

the elements constituting alloy must be isomorphous: even crystallographic structure (Cubic with centered faces with cubic with centered faces, of a Cubic centered with cubic centered, Hexagonal compact with hexagonal compact).
the Atome S must have a close size: their rays should not differ of more than 15%. In the contrary case solubility will be very limited.
the valence of the two elements must be identical.

Example: the Bismuth and the Antimony

The antimony and bismuth alloys form a solid solution (in lower part of the solidus) in all the cases of figure and at all the temperatures. The Diagramme of phase is a diagram with a spindle. Some other couples of which miscibility is good and makes it possible to obtain homogeneous solid solutions at all temperatures: Copper - Nickel, copper palladium, Money - Gold, money - palladium, Molybdenum - Vanadium, molydène- Tungsten etc

Certain soluble binary alloyings present to the lowest temperatures a defect of solubility. It appears on the diagram of phase a sector where two phases cohabit, the first consisting of a solid solution saturated with B in has, the second conversely has in B. It is the case for example system copper-nickel which presents in lower part 322°C a zone with two phases 1 and 2.

Structure of an alloy

Homogeneous alloy

A homogeneous alloy can be ordered (the atoms of various natures follow a strict alternation) or disordered (the various atoms occupy of the random places).

In general, there is a majority metal, other metals are called “elements of alloy”. The atoms of the alloy elements can take the place of the atoms of majority metal, one speaks then about “substitution”; they can also slip between the atoms of majority alloy, one speaks about “insertion”. When a metal is present in low content in an alloy, one often speaks about solid Solution.:: * The dogs are animals

Heterogeneous alloy

When the content of alloy element increases, one can have formation of two phases: a phase containing few alloy elements, and a phase with strong content of alloy elements. The Cristallite S with strong content are called “precipitated”.

The Précipité S are often ordered alloys, which one calls “intermetallic”. The intermetallic ones thus formed are studied sometimes thereafter as clean alloys, like a new material, and one tries to produce some as such and either as precipitates.

Examples of alloys

Principal alloys

Alloys of Iron

* cast iron: Iron + Carbon (with more than 2,1% and up to 6.7% in carbon mass)

* Steel: iron + carbon (with less than 2,8% in carbon mass)

* Stainless steel: iron + nickel+ Chromium, and sometimes, Molybdenum, Vanadium

cuani (2.7 OF cast iron and 2.9 of nickel)

Alloys of copper

* Bronze: Copper + tin; the Airain is the old name of bronze

* Laiton: copper + Zinc

* Dolomite: copper + rockwool + nickel

* Ebonite: copper + iron + chromium + calcium

Alloys of Aluminum

They are also called light alloys

For more detail to see the two articles below:

* Alloys of aluminum for welding

* Alloys of aluminum for foundry

Less known alloys

Alloy lead-tin: for the welding
Amalgam: mercury + another metal, for example Gold or coppers; the term also indicates a mixture of metals used for the dental care (“leading”)
Maillechort: copper + zinc + nickel
Monel ® (trade name): nickel + copper
Babbit metal: tin or Lead + Antimony
Zamak: zinc + aluminum + magnesium + copper

Alloys for specific applications

Ferrotitaniums: iron + 25 with Ti 70%m + 4 with aluminum 10%m
TA6V: Titanium + 6%m Aluminum + 4%m vanadium, very much used in the aircraft industry.
Nota: usual designation French TA6V is based on old standard NF has 02-004 cancelled today, its chemical designation is Ti Al 6 V.
MCrAl: metal + chromium + aluminum + sometimes of the Yttrium (MCrAlY), alloys considered for their good mechanical resistance and resistance to the Corrosion at high temperature)

FeCrAl: iron + chromium + aluminum
NiCrAl: nickel + chromium + aluminum

superalloys at base nickel (for example the Inconel S): good mechanical resistance and corrosion resistance at high Intermetallic temperature
S: ordered alloys, respecting a stoichiometry specifies (but variations with stoichiometry are tolerated)

NiAl β: 50%at nickel + 50%at aluminum
B2 Ferroaluminium: 50%at iron + 50%at aluminum
TiAl: 50%at titanium + 50%at aluminum

alloys presenting of low dilation coefficients (Inventor Charles Edouard Guillaume)

Invar (nickel 36%, manganese 0,4%, carbon 0,1%, iron 63,5%)
elinvar (Nivarox, Métélinvar, Isoval) (nickel, chromium, iron)

FeNiCo : the Kovar, an alloy Fe/Nickel/Cobalt intended for sealing glass/metal or ceramics/metal

the Memory-shape alloys:

NiTi : 50% Nickel + 50% titanium
CuZnAl: 70% Copper + 25% Zinc + 5% aluminum
CuAlNi: 82% copper + 12% aluminum + 4% nickel
CuALBe: copper + aluminum + Béryllium

Mythical alloys

Adamantium : alloy very much used in the novels and the cartoons of Science fiction (Wolverine, Ultron)…
Vibranium: alloy also used in the cartoons American Comics (Captain America.)
Orichalch: mythical alloy of the Greek antiquity, often associated with the Atlantis, whose one does not know the composition.