Eutectic alloys are those in which a minimum melting point is achieved. The word “eutectic” comes from the Greek eu, meaning “good”, and tektos, meaning “melting”. The eutectic temperature is the temperature at which the solid and liquid phases of an alloy are in equilibrium. The eutectic composition is the composition of an alloy that melts at the eutectic temperature.
Alloys with a eutectic composition can be made to melt at any lower temperature by adding more of one or more other element(s). For example, pure sodium has a melting point of 97.72 °C (207.37 °F), but when added to potassium, forms NaK, which has a melting point of only -12.6 °C (-24.7 °F). By adding small amounts of cesium to NaK, it is possible to lower its melting point even further, to -78.5 °C (-109.3 °F). Cesium does not form a stable compound with sodium at any other ratio; therefore, this mixture’s properties cannot be predicted from knowledge of its constituent elements alone – it exhibits non-ideal behaviour due to immiscibility between its two components during solidification (although they are perfectly miscible in the liquid state). Alloys with a eutectoid composition can be made to solidify at any higher temperature by adding less of one or more other element(s). For example, pure iron has a freezing point (solidus) of 1538 °C (2802 °F), but when carbon is added to form steel, its freezing point drops significantly, to below 1000 °C (1832 °F). This happens because carbon atoms tend to occupy interstitial sites within the iron lattice as Solid Solution hardeners rather than forming their own separate phase as would happen if there were enough carbon for it all To precipitate out as graphite; this lowers the overall energy required for atoms within the metal lattice To vibrate about their mean position (i.e., decreases thermal conductivity), thus raising the melting point slightly while decreasing the freezing point dramatically due to decreased thermal stability imparted by solution hardening effects..
The term “eutectoid” refers specifically To alloys whose compositions lie on or very close To either side of their respective equilibrium points In binary phase diagrams where just two elements are considered; however, similar behaviour can occur in multicomponent systems where more than two elements are involved if certain conditions are met. When an alloy contains several different types Of atom arranged randomly throughout its structure – i.,e., it Is amorphous – then no long-range order exists And such materials generally have extremely low melting points well below those Of their crystalline counterparts; metallic glasses typically exhibit glass transition temperatures around 650 K (−420 °C; −840 ̊ F) regardlessOf chemical composition..