Definition, Classification, and Formation of Alloys
– An alloy is a mixture of chemical elements, with at least one being a metal.
– Alloys retain the properties of metals, such as electrical conductivity and luster.
– Alloys can have different properties from pure metals, such as increased strength or hardness.
– Some alloys can reduce the overall cost of materials while preserving important properties.
– Metallic bonding, rather than covalent bonds, joins the atoms in an alloy.
– Alloys are classified as substitutional or interstitial, depending on the atomic arrangement.
– They can be homogeneous (single phase) or heterogeneous (two or more phases).
– Alloys can be solid solutions or mixtures of metallic phases.
– The constituents of alloys are measured by mass percentage or atomic fraction.
– Intermetallic alloys have a specific atomic arrangement and distinct properties.
– Alloys are formed by mixing two or more elements, with one being a metal.
– The mechanical properties of alloys can be different from those of their constituents.
– Alloys can form solid solutions or have a heterogeneous microstructure.
– Impurities in alloys are introduced from base metals and alloying elements.
– Care is taken to remove impurities during the alloying process to ensure desired properties.
Examples and Applications of Alloys
– Red gold (gold and copper) and white gold (gold and silver) are examples of alloys.
– Sterling silver is an alloy of silver and copper.
– Steel is an alloy of iron with non-metallic carbon or silicon.
– Brass, pewter, duralumin, and bronze are also examples of alloys.
– Amalgams, like dental fillings, are alloys.
– Steel alloys are used in buildings, automobiles, and surgical tools.
– Titanium alloys are used in the aerospace industry.
– Beryllium-copper alloys are used for non-sparking tools.
– Alloys are used in the production of gate valves, such as those made from Inconel.
– Alloys have a wide range of applications in various industries.
Properties and Alloying Elements
– Alloys are strong solvents capable of dissolving most metals and elements.
– They readily absorb gases like oxygen and burn in the presence of nitrogen.
– Alloys must be melted in vacuum induction-heating and special, water-cooled, copper crucibles to avoid contamination.
– Alloying can be performed with constituents in a gaseous or solid state.
– Adding another element to a metal creates internal stresses in the lattice of metallic crystals, enhancing properties like strength.
– Alloying elements are added to induce hardness, toughness, ductility, or other desired properties.
– Most metals and alloys can be work hardened by creating defects in their crystal structure.
– Alloys can have their properties altered by heat treatment.
– Aluminium, copper, magnesium, titanium, and nickel alloys can be strengthened by heat treatment.
– Steel undergoes a change in atomic arrangement when alloyed with carbon, forming austenite.
Heat Treatment and Melting Range of Alloys
– Annealing can soften most metals by recrystallizing the alloy and repairing defects.
– Controlled heating and cooling can harden certain alloys.
– Steel undergoes a diffusionless transformation when rapidly cooled, forming martensite.
– Precipitation hardening alloys soften when quenched and then harden over time.
– Age hardening alloys, like duralumin, became widely used in the construction of modern aircraft.
– Most alloys do not have a single melting point, but a melting range.
– The temperature at which melting begins is called the solidus.
– The temperature when melting is complete is called the liquidus.
– Eutectic mixtures or peritectic compositions can give alloys a unique and low melting point.
– Alloys may have no liquid/solid slush transition during melting.
History, Examples, and Notable Alloys
– Alloys have been used by humans since ancient times.
– The use of alloys started with meteoric iron, a naturally occurring alloy of nickel and iron.
– Bronze and brass are examples of alloys.
– Ancient civilizations alloyed metals for aesthetic and practical purposes.
– Pewter, an alloy primarily consisting of tin, has been used for various objects.
– Meteoric iron was used by ancient people to make tools, weapons, and nails.
– Bronze is an alloy of copper and tin.
– Tin was rare and mostly found in Great Britain.
– Copper was often alloyed with zinc to form brass.
– Mercury dissolves many metals to form amalgams.
– Amalgams have been used for gilding objects since ancient times.
– Gold was often alloyed with copper or iron for aesthetic purposes.
– Copper was added to silver to make sterling silver.
– Steel production in ancient times was limited due to the inability to fully melt iron.
– The introduction of blister steel during the Middle Ages allowed for the production of steel in larger quantities.
– Benjamin Huntsman’s crucible steel process in 1740 enabled mass production of tool steel.
– The blast furnace in the Middle Ages allowed for the production of pig iron, which could be melted to create steel.
– Henry Bessemer’s process of blowing hot air through liquid pig iron reduced the carbon content and led to large-scale steel production.
– Alloy steel refers to steels that contain elements like vanadium, molybdenum, or cobalt, which alter the properties of the base steel.
– Steel production methods were often kept as closely guarded secrets, limiting the understanding of steel as an alloy until the 1930s-1970s.
– Benjamin Huntsman experimented with adding elements like manganese to steel to remove impurities.
– Robert Hadfield developed mangalloy, the first commercially viable alloy steel, containing around 12% manganese.
– Tungsten carbide steel, developed by Taylor and White, replaced Mushet’s high-speed steel due to its superior properties.
– Aluminium extraction processes in the 19th century often resulted in unintended aluminium-copper alloys.
– Aluminium alloys gained practical use when the Wright brothers used Source: https://en.wikipedia.org/wiki/Alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opacity, and luster, but may have properties that differ from those of the pure metals, such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength.
In an alloy, the atoms are joined by metallic bonding rather than by covalent bonds typically found in chemical compounds. The alloy constituents are usually measured by mass percentage for practical applications, and in atomic fraction for basic science studies. Alloys are usually classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy. They can be further classified as homogeneous (consisting of a single phase), or heterogeneous (consisting of two or more phases) or intermetallic. An alloy may be a solid solution of metal elements (a single phase, where all metallic grains (crystals) are of the same composition) or a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within the metal).
Examples of alloys include red gold (gold and copper), white gold (gold and silver), sterling silver (silver and copper), steel or silicon steel (iron with non-metallic carbon or silicon respectively), solder, brass, pewter, duralumin, bronze, and amalgams.
Alloys are used in a wide variety of applications, from the steel alloys, used in everything from buildings to automobiles to surgical tools, to exotic titanium alloys used in the aerospace industry, to beryllium-copper alloys for non-sparking tools.
