Ultrafine-grained copper alloy with remarkable improvement in strength and thermal stability at high temperatures

In traditional dispersion-strengthened (DS) copper alloys, inert nanoparticles selected as strengthening phase were noncoherent or semi-coherent with the matrix. In this work, high-density YbAlO3 ceramic nanoparticles (NPs) with an average size of ∼6 nm were introduced into copper matrix by mechanical alloying and spark plasma sintering. Microstructural characterizations confirm that YbAlO3 NPs with different size are all fully coherent with the matrix and have a superlattice structure, and the coherency strain remains constant with the size increasing of the NPs. The extremely low lattice mismatch between the NPs and Cu prevents the NPs from coarsening even annealing at 900 °C (0.87 Tm), which leads to remarkable improvement in strength and thermal stability of the alloy at high temperatures. The tensile strength of the alloy reaches up to 585 MPa at 300 °C and 449 MPa at 450 °C, over two times higher than other DS copper alloys. Moreover, no grain growth and dislocation density reduction occurs after annealing at 900 °C for 3 h, demonstrating an excellent thermal stability of the alloy. This work proves the significant advantages of fully coherent NPs for DS materials and provides a new pathway for designing materials intended to serve at high temperatures.