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 La 0.005 Al 0.17 FeCoCrNiMn 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 LaAl 1.06 Ni 3.94 phase. Subsequently, two types of precipitated phases were observed during the aging treatment: (1) the Cr-rich M 23 C 6 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 LaAl 1.06 Ni 3.94 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. • The large size AlNi and RENi phases were avoided via rapid solidification when RE or Al added into the FeCoCrNiMn HEAs. • The forming ability of LaAl 1.06 Ni 3.94 phase has been systematically described via the Miedema's and Toop's model. • The crystallographic orientation relationships of the precipitated phases for strengthening were clearly determined. • Rapid solidification method is an efficient way to the application of RE or Al element in the FeCoCrNiMn HEAs. [ABSTRACT FROM AUTHOR]