Both alloys and composites are at least two components mixtures. Though, there are also more than a few differences between them that make them suitable for different applications. Alloy is a combination of two or more components, one of which has to be metallic. The purpose of putting these two (or more) ingredients together is creating a mixture that will have significantly different (better) qualities than the isolated components. Still, the present technologies often have requirements that cannot be met by conventional alloys. Many industries today need materials that are characterized with better mechanical properties such as low density, high strength, resistance to abrasion and corrosion. This combination of properties can be realized with composite materials.

Composites, similarly, are a combination of two or more ingredients, but metals are not necessarily included in their formation. These constituents (which are both physically and chemically diverse) are put together in order to generate a composition that is stronger than the original elements. Beside the synthetic (man-made) composites, there are also natural composites (e.g. wood, bones, and teeth).

What is Alloy?

Metals and alloys are materials that are characterized by a number of specific features, due to which they have become the foundation of modern technology. Metals consist of pure chemical element with a small amount of other element addition. They are portrayed by characteristic metal gloss, increased electrical and thermal conductivity, good mechanical properties, resistance to electrochemical influences and elevated temperatures, susceptibility of different techniques’ processing (treating) in both cold and heated conditions and so on. All of the listed characteristics are conditioned by the properties of the internal structure of the atoms and their interconnections. The metal density ranges between 0.59 g/cm³ (lithium) and 22.4 g/cm³ (osmium). Metal with the highest melting temperature point is tungsten (3400⁰C), while mercury is with the lowest one (- 39⁰C).

Alloys are complex materials composed of a base element and metals or non-metals. The alloying elements are called alloy components, and their number and specifics determine the complexity of the alloy and its characteristics. A metal (at least one) enters the composition of alloys (e.g. bronze: copper and tin alloy, steel: iron and carbon alloy, etc.). Alloys acquire completely new characteristics, which differ from the ones of their components: more favorable mechanical properties, increased corrosion resistance, color change, improved processing ability, etc. Most of the alloys are obtained by melting the constituents, but there are other methods as well – such is the case of metal-ceramic alloys that are made by sintering.

In industrial practice, pure metals are often substituted with alloys. The reasons are multiple: technically pure metals are difficult to obtain in purified state, they are expensive, generally have low damping capacity and strength levels, unfavorable chemical and physical properties, are often difficult to handle with standard processing methods and many more.

What is Composite?

Composites are formed from composite materials, e.g. by casting, laminating or extruding. Composite material is a type of material consisting of a combination of two or more simple (monolithic) materials and in which the individual components retain their distinctive identity. The composite material has properties different from the properties of its components – the simple materials. This often means that the physical properties are improved because the main technological interest is obtaining materials with superior physical (usually mechanical) properties in relation to the properties of the components. In principle there are two phases (components) in the composite material: the matrix and the reinforcement. These segments have significantly different mechanical properties. The matrix is ​​softer and serves as a filler to achieve stability of the shape of the hard phase. The reinforcement is the solid and hard component. Depending on the matrix, composites are divided into: metals, ceramics and polymerics. All constituents can be continuous, or can be dispersed in a continual matrix. In the last case it is necessary to establish a lower limit for the size of the dispersed phase below which the material is considered to be monolithic. Examples of frequently used composites are:

• with particle addition – hard-sanding alumina particles of aluminum oxide Al2O3 or silicon carbide SiC bonded with a glass or polymer matrix in a solid plate;
• with fiber addition – plastic (epoxy or polyester resin) reinforced with glass fibers;
• structural composite – alternating layers in “plywood” of thin layers of wood and wood glue (polymer).

Alloys have the following advantages:

• low weight
• excellent resistance to fatigue loads
• high temperature resistance
• extremely long lasting
• low or no plasticity compared to metals which deform and mold caused by high loads
• can provide a strength and weight ratio of up to 20%
• more resistant to loads during thermal activity,  as they almost do not have thermal expansion and retain the original shape during temperature increasement
• offer the possibility of parts connection during the production process itself
• resistant to corrosion, long lasting, and have dimensional stability in extreme working conditions
• non-metal composite materials are non-magnetic and can be used in sensitive electronic elements environment. Besides, they are not electrically conductive so they can be in touch with electronics

Difference Between Alloy and Composite

• Structure

Alloy is combination of materials – mix of two or more metals or metal with non-metallic element. Its physical properties intermediate between those of the constituent metals; but the chemical properties of each element remain unaffected. The mixture can be separated by physical means. A composite is also formed from several elements (a metal can be part of the mixture but not necessarily). Elements can be returned to their original state by chemical reactions.

• Characteristics

An alloy is essentially the same material with extra qualities. Mixtures are formed from components with the purpose of enhancing the qualities than the constituents. Alloying permanently changes the physical characteristics of the metals and some of the advantages that can be achieved are increased resistance to corrosion and oxidization, changing the electrical properties, improved strength, a higher or lower melting point compared with the constituent metals and so on. A composite is a combination of materials to form an entirely new material (with altered qualities). The new material may be more robust, lighter, or cheaper than the original components.

• Application

Depending on the structural compounds and the techniques/methods used in the production process, both the alloys and composites manifest different characteristics and can have different applications respectively.

Alloy vs. Composite

Summary

• Sometimes pure metals do not have the satisfactory mechanical and technological properties (for example for the manufacture of machine elements and tools and in the construction industry) and are therefore not used as such. This is where alloys and composites have proven to be of a great significance
• The alloys are made up of at least two components in which the basic component is metal, while the other components may be metallic but also nonmetallic. The new material results in enhanced characteristics – such as better corrosion resistivity, improved conductivity, lightness, greater cost-efficiency and so on
• A composite material is a system composed of two or more components with different configurations, one of which is the matrix or the base material (polymer, ceramic or metal), to which the second component is added (fiber, nano-tube, plate, spherical particle) to achieve the necessary combination of properties (stiffness, density, rigidity, hardness, thermal and electrical feasibility).
• Both alloys and composites have numerous advantages – depending on the materials and techniques used. Some of the improvements are light weight, high strength and strength related to weight, corrosion resistance, high-impact strength, dimensional stability, durability etc.

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