The microstructure of the as-cast sample, as shown in Fig. 3, is mainly composed of coarse dendrite crystals with a small amount of black precipitate. The corresponding EDS analysis revealed that Co, Cr, and Ni were homogeneously distributed in the sample, while the black precipitate contained high levels of Al and Ti. This segregation may be due to the negative mixing enthalpies of Al and Ti in the alloy, which causes their accumulation near phase boundaries. Studies have also indicated that Al and Ti can form hard atomic clusters by bonding strongly with surrounding transitional metals in as-cast Fe4CrNi (AlTi)0.6 HEAs. The EBSD inverse pole figure further confirms that the microstructure displays typical characteristics of coarse dendrite grains with an average size of approximately 57 μm. The fraction of HAGBs (θ≥15º) and LAGBs (2<θ<15º) was indicated at the top right corner of Fig. 3(h), where LAGBs comprised 98% of all grain boundaries analyzed. A higher fraction of LAGBs suggests a higher dislocation density since these boundaries are essentially composed of dislocation arrays [ ].
