Microstructure control and strength improvement of La0.005Al0.17FeCoCrNiMn high entropy alloy by rapid solidification and aging treatment

Precipitation strengthening, which requires controlling the type, size, and distribution of precipitation particles, is attractive for high-entropy alloys (HEAs). Here, we demonstrate an effective approach for the secondary phase precipitation of La0.005Al0.17FeCoCrNiMn HEAs by rapid solidification and aging treatment. The supersaturated La and Al atoms were present in the face-centered-cubic (FCC) matrix via rapid solidification, which prevented the formation of large size secondary phases. The homogenization heat treatment promoted the disappearing of the dendritic structure and the precipitation of the LaAl1.06Ni3.94 phase. Subsequently, two types of precipitated phases were observed during the aging treatment: (1) the Cr-rich M23C6 phase, which was distributed along the grain boundary and coherent with the FCC matrix; and (2) the Cr-rich σ phase, which connected with the LaAl1.06Ni3.94 phase via the periodic stacking faults between them. The forming abilities of the ternary La-Al-Ni interphase have been systematically described based on the Miedema’s and Toop’s model. The microhardness reached 156 HV and the tension strength increased from 343 MPa to 437 MPa after the aging treatment. This work provides a fundamental research basis for controlling the precipitation strengthening of HEAs.