Abstract
This work aimed to examine the structure of Cu-Y₂O₃ composite, analyse the fracture mechanism, and propose the model of fracture. The in-situ tensile test in SEM was used for direct observation of the process of deformation and fracture. Microscopic analysis revealed that Cu matrix grains are spherical with a mean diameter of ∼ 500 nm. EDX and selected area electron diffraction confirmed the presence of Y₂O₃ particles. Particles can be divided, according to the size, into two categories: smaller A (up to 20 nm) and more significant B (20–100 nm). The in-situ tensile test in SEM showed that the first cracks were created on the particle-matrix interfaces and in the triple point. Subsequent coalescence was observed, and we assumed that the cracks propagate along the grain boundaries. The fracture surface has a transcrystalline ductile character. Based on the in-situ observations and analysis, we proposed the model of fracture mechanism.

Key words
Cu composite, Y₂O₃, high-resolution scanning transmission electron microscopy (HRSTEM), structure, fracture mechanism

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