Alloy and Composite

Alloy and composite materials are mixtures of two or more components. Both have different properties than the starting materials.

What is an Alloy?

Alloy is a mixture of two or more elements where at least one of them is metal. The resulting alloy can be a solution or a solid. If only two components are mixed to produce an alloy, it is known as a binary alloy. If there are three components, it is known as ternary alloy. The amount of element in the alloy is normally measured and given by mass (as percentages). Alloys can be also classified as homogeneous if they have a single phase. If have several phases, those alloys are classified as heterogeneous. If there isn’t a distinct phase boundary, then they are known as intermetallic.

Alloys are produced from elements, to have improved qualities than the reactant elements. They have different qualities than the reactant components. Normally alloys have metallic properties, but they differ from pure metal elements. For example, alloys don’t have a single melting point. Rather, they have a range of melting points.

Steel is an example for alloy. It is made out of iron and carbon. Steel is stronger than iron. The carbon percentage can vary depending on the grade, and mostly it is between 0.2% and 2.1% by weight. Though carbon is the main alloying material for iron, some other elements like Tungsten, chromium, manganese can also be used for the purpose. Different types and amounts of alloying element used determine the hardness, ductility and tensile strength of steel. Alloying element is responsible for maintaining the crystal lattice structure of steel by preventing dislocation of iron atoms. Thus, it acts as the hardening agent in steel. The density of steel varies between 7,750 and 8,050 kg/m3 and, this is affected by the alloying constituents too.

Brass is another alloy which is made out of copper and zinc, but more durable than copper and attractive than zinc. When producing jewelry from gold, silver, and platinum, they are mixed with other elements, to make them more ductile and flexible.

What is a Composite?

Composite is a material made out of two or more constituent materials which are chemically and physically different. Constituent materials are the individual materials which makes the composite. There are two categories of them as matrix and reinforcement. Usually matrix material supports the reinforcement material. The constituent materials stay separately within the finished structure because they are chemically and physically different, to mix with each other.

Composites can be synthetic or naturally occurring materials. Wood is a natural composite. It is made up of cellulose fibers and a matrix of lignin. When preparing composites, normally both matrix and reinforced materials are combined and compacted. After this, the shape of the composite is set, and it won’t change unless it is affected by certain conditions.

Alloy vs Composite

• Alloy is a homogenous or a heterogeneous mixture whereas composites are heterogeneous.

• There is at least one metal in alloy, but it is not necessary to have metals in composites.