Early research of HEA was focussed on forming single-phased solid solution, which could maximize the major features of high entropy alloy: high entropy, sluggish diffusion, severe lattice distortion, and cocktail effects. It has been pointed out that most successful materials need some secondary phase to strengthen the material, and that any HEA used in application will have a multiphase microstructure. However, it is still important to form single-phased material since a single-phased sample is essential for understanding underlying mechanism of HEA and testing specific microstructure to find structure producing special properties.