Coherent intergranular precipitates overcome intermediate-temperature embrittlement of a L1₂-strengthened medium-entropy alloy

Polycrystalline high/medium entropy alloys (HEA/MEAs) strengthened by dense L1₂-structured nanoparticles have demonstrated significant promise for high-temperature structural applications. However, their widespread adoption is hindered by severe intergranular embrittlement starting from intermediate temperatures. In our present work, we introduce coherent intergranular D0₁₉-structured precipitates into a polycrystalline L1₂-strengthened MEA to address such thorny problem. Unlike conventional polycrystalline counterparts that suffer from pronounced intergranular embrittlement, the newly developed structure exhibits exceptional resistance to intergranular fracture at an intermediate temperature of 800 °C. At this temperature, our designed alloy exhibits a superior yield strength of ∼ 713 MPa and excellent fracture elongation of ∼ 24.3 %. Microstructural analysis reveals that the enhanced ductility arises from the suppressed cracking by coherent intergranular precipitates, in combination with the high-density heat-assisted twinning facilitated by Nb segregation. These findings provide a novel strategy for the design of high-temperature structural materials.