PNNL

Abstract

A high-strength Co-free triple-phase Al10Cr12Fe35Mn23Ni20 high entropy alloy (HEA) was successfully deposited using Friction Surface Layer Deposition (FSLD), a bulk manufacturing method. A meticulous process parameter optimization was performed by fabricating multiple single-layer deposits by changing the forging force and traverse speeds. The optimized parameters were then used to manufacture a scaled-up multi-layer specimen. The starting microstructure of the HEA comprised coarse grains of the soft FCC phase, long columnar dendrites of the hard BCC phase, and small precipitates of the harder B2 phase within the BCC dendrites. Detailed microstructural characterization was performed to understand the unique microstructural characterization pathways for the hard and soft phases during FSLD. The softer FCC matrix underwent continuous dynamic recrystallization, forming finer equiaxed grains due to high-temperature severe plastic deformation. Concurrently, the BCC dendrites fractured into smaller fragments, and in some regions, these smaller fragments grew marginally, changing their morphology from arbitrary to hourglass-like. In contrast, the B2 precipitates within the BCC fragments dissolved during the elevated temperatures of FSLD and reprecipitated as substantially finer precipitates during continuous cooling post-FSLD. The substantially refined grains/precipitates not only improved the hardness from 177 HV to 283 HV due to Hall-Petch strengthening but also increased the number of interfaces in the FSLD-processed HEA. The overall increase in the number of interfaces, including the coherent interfaces between the BCC and B2 phases, potentially enhances the sink strength/radiation tolerance of the HEA, making it a suitable candidate for future nuclear applications.