High Entropy Alloys

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Humans have been using metals and alloys since a long time. Arguably, bronze was the first alloy that impacted humanity. Since then, humans have developed a large number of alloys and alloy systems. What we can call conventional alloys, are based on one or two principal elements. Other alloying elements are added to the principal element to impart the now formed alloy with desired properties, forming an alloy family based on the principal elements. However, the number of elements in the periodic table which can be used for such conventional alloying is limited, thus the alloy families we can develop are also limited. Here comes the concept of High Entropy Alloys. High Entropy Alloys or HEAs for short, are alloying systems …show more content…

Basically it says that the properties of HEAs cannot just be taken from averaging the properties of the constituting elements. There will also be some effects on the properties from the interaction between different elements and phases as well as from the lattice distortion effect, which at first may seem unintuitive. This cocktail effect then gives many possibilities for materials with different properties. 1.2 Phase and Crystal Structure The phases are classified according to their structure (simple/complex) and ordering (ordered/disordered). A phase is said to be simple if its structure is identical to or derived from FCC, BCC or HCP structures. If a phase is not simple (e.g. Laves phases), it is said to be complex. Therefore, the above three types now become: simple disordered phase (SDP), simple ordered phase (SOP), and complex ordered phase (COP). To the Surprise of most people, simple structures (SDPs and SOPs) are the most frequently seen in as-cast HEAs. These simple phases originate from the High-entropy effect mentioned previously. Besides simple Phases, different kinds of cops, such as σ, μ, laves, etc., are also observed in …show more content…

Factors that affect the formation of binary solid solutions include atomic size difference, electron concentration, and difference in electronegativity. Besides these factors, enthalpy and entropy of mixing are the most important phase formation 6 parameters for HEAs. The formation of simple or complex phases depends mainly on the enthalpy of mixing (Δ Hmix), entropy of mixing (Δ Smix), and atomic size differences (δ). In order to form sole simple phases (i.e. FCC, BCC, and their mixtures, including both ordered/disordered cases), the following conditions have to be met

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