Eliminating room-temperature brittleness via introducing residual interface defects to control element diffusion pathways

Aging treatment can significantly enhance the strength of aging-hardening alloys, but may also result in room temperature brittleness (RTB) due to the simultaneous precipitation of brittle phases at grain boundaries (GBs). This work used a novel strategy involving remelting pre-nanoprecipitates to generate residual interface defects and then to control the diffusion of elements, by using Cu-9Ni-6Sn-0.6Cr alloy as the research object. These residual defects can capture and preferentially precipitate the nanoprecipitates forming elements locally during the re-aging process to prevent their diffusion to the GBs, thereby suppressing brittle phases formation at GBs and eliminating RTB behavior. Tensile testing results show that compared to the alloy without preaging and remelting treatments, the fracture elongation of the alloy after preaging-remelting-re-aging process increases from v3.2 % to similar to 18.6 % (an increase of similar to 480 %), and the ultimate tensile strength increases synergistically from similar to 750 MPa to similar to 1000 MPa (an increase of similar to 260 %). This synergistical improvement in strength and ductility results from inhibiting D0(3) phases formation at GBs and high-volume fraction of the nanoprecipitates within the grains. The formation of residual interface defects is due to the asynchronous annihilation of interface defects and dissociation of enriched elements during remelting process, and is affected significantly by the heating speed during remelting treatment. Too slow or fast heating speed suppresses defect formation, while appropriate heating speed favors the preferential dissociation of enriched elements. This new strategy is beneficial for developing high-performance structural materials with both high strength and large ductility.