<P> Alloying a metal is done by combining it with one or more other elements . The most common and oldest alloying process is performed by heating the base metal beyond its melting point and then dissolving the solutes into the molten liquid, which may be possible even if the melting point of the solute is far greater than that of the base . However, some metals and solutes, such as iron and carbon, have very high melting - points and were impossible for ancient people to melt . Thus, alloying may also be performed with one or more constituents in a gaseous state, such as found in a blast furnace to make pig iron, nitriding, carbonitriding or other forms of case hardening, or the cementation process used to make blister steel . It may also be done with one, more, or all of the constituents in the solid state, such as found in ancient methods of pattern welding, shear steel, or crucible steel production, mixing the elements via solid - state diffusion . </P> <P> By adding another element to a metal, differences in the size of the atoms create internal stresses in the lattice of the metallic crystals; stresses that often enhance its properties . For example, the combination of carbon with iron produces steel, which is stronger than iron, its primary element . The electrical and thermal conductivity of alloys is usually lower than that of the pure metals . The physical properties, such as density, reactivity, Young's modulus of an alloy may not differ greatly from those of its base element, but engineering properties such as tensile strength, ductility, and shear strength may be substantially different from those of the constituent materials . This is sometimes a result of the sizes of the atoms in the alloy, because larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation . Sometimes alloys may exhibit marked differences in behavior even when small amounts of one element are present . For example, impurities in semiconducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura . Some alloys are made by melting and mixing two or more metals . Bronze, an alloy of copper and tin, was the first alloy discovered, during the prehistoric period now known as the Bronze Age . It was harder than pure copper and originally used to make tools and weapons, but was later superseded by metals and alloys with better properties . In later times bronze has been used for ornaments, bells, statues, and bearings . Brass is an alloy made from copper and zinc . </P> <P> Unlike pure metals, most alloys do not have a single melting point, but a melting range during which the material is a mixture of solid and liquid phases (a slush). The temperature at which melting begins is called the solidus, and the temperature when melting is just complete is called the liquidus . For many alloys there is a particular alloy proportion (in some cases more than one), called either a eutectic mixture or a peritectic composition, which gives the alloy a unique and low melting point, and no liquid / solid slush transition . </P> <P> Alloying elements are added to a base metal, to induce hardness, toughness, ductility, or other desired properties . Most metals and alloys can be work hardened by creating defects in their crystal structure . These defects are created during plastic deformation by hammering, bending, extruding, etcetera, and are permanent unless the metal is recrystallized . Otherwise, some alloys can also have their properties altered by heat treatment . Nearly all metals can be softened by annealing, which recrystallizes the alloy and repairs the defects, but not as many can be hardened by controlled heating and cooling . Many alloys of aluminium, copper, magnesium, titanium, and nickel can be strengthened to some degree by some method of heat treatment, but few respond to this to the same degree as does steel . </P>

Chemistry project to study the constituents of an alloy pdf