Novel AlCrFeNiNb0.3 high entropy alloy: Microstructure, properties and an unknown Nb-rich intermetallide

Novel AlCrFeNiNb0.3 high entropy alloy (HEA) was cast, heat treated and thoroughly investigated. This alloy exhibits microstructural stability up to 1300 degrees C and exceptional high hardness values. It is plausible to assume that the reason for these results is relatively large amount of intermetallic phases appearing in this alloy. AlCrFeNiNb0.3 solidifies dendritically. The interdendrite region exhibited typical ternary eutectic microstructure, containing Laves phase, BCC and B2. Dendrite cores were found to be of two types containing either BCC particles embedded in the B2 matrix or vice versa - B2 particles embedded in the BCC matrix. Regardless the type of dendrite's microstructure, this area also contained small particles of highly defected Laves phase and additional Nb-rich nanosized particles with an unknown structure. Latter had faceted rectangular shape with a length of 327 +/- 100 nm and width of 70 +/- 20 nm. Crystal structure of the unknown phase was investigated by means of electron crystallography and was characterized as cubic, Fm (3) over barm, with a = 11.61 angstrom. Structure type was assigned here as Th6Mn23, due to the similarity of lattice parameters and the space group, but it requires further investigation.