A novel strategy to regulate the precipitation-strengthened high-entropy alloy fabricated by laser directed energy deposition

Abstract

The optimization of the aging process is an effective strategy for achieving excellent performance in the rapidly solidified CoCrFeNiTi0.7 high-entropy alloy (HEA). Current research has clearly demonstrated that the unique design of the high-low duplex aging (HLDA) strategy plays a crucial role in achieving outstanding wear resistance in additive manufacturing of the rapidly solidified CoCrFeNiTi0.7 HEA. The microhardness of the SA-750 and HLDA samples increased to approximately 678 HV and 729 HV, respectively, compared to the as-deposited sample (LDED) with a microhardness of approximately 506 HV. Additionally, the wear rates of the SA-750 and HLDA samples were reduced by approximately 17.1% and 24.7%, respectively, compared to the LDED sample. This remarkable improvement in wear resistance can be attributed to the introduction of high-density nanoscale core-shell microstructures formed by secondary η2 and L12-γ' phases. Furthermore, when compared to the grain size of SA-750 (65.63 μm), the HLDA sample exhibited the precipitation of cellular precipitates at the grain boundary, and the grain size (68.46 μm) did not show significant growth or coarsening. This demonstrates the precise control of the matrix grain size achieved in our study. Therefore, the high-low duplex aging treatment has been validated for developing high-performance rapidly solidified CoCrFeNiTi0.7 HEA. This strategy provides a targeted approach for tissue design to tap into the maximum potential of additive manufacturing precipitation-strengthened HEAs.