**3.4 The Cocktail effect**

Cocktail effect is a postulate, first identified by Prof. S. Ranganathan [20]. It refers to the unpredictable improvement in properties of materials based on the synergy of multi principal alloying elements. The properties range from near zero thermal expansion, ultra-high strength, corrosion resistance, good fracture toughness, ductility to photovoltaic effects or thermo-electronic responses [5]. This effect reminds about the acceptance of unique properties formed due to unusual combinations of elements as observed in MPEAs.

#### **3.5 The short-range ordering**

Besides these effects, chemical short range ordering (CSRO) has a significant impact on the mechanical properties, as it is proved to facilitate phase transformations in HEAs [21]. The CSRO has direct correlation with the activation energy of phase transformation from FCC to HCP phase in CoCrNi alloys [22]. The presence of SRO increases the Stacking Fault Energy (SFE) and yield strength in several alloys; it has been proved for CoCrNi alloys both experimentally and computationally [21–23]. A study using reverse Monte-Carlo suggests that the presence of SRO in TiVNb alloys is responsible for forming the FCC supercells in the alloy [21, 24].

All the empirical parameters discussed in above sections are calculated on the basis of available information in **Table 1**.
