In-situ observation of Ni-11.5 wt%Si eutectic microstructure evolution and exploration of strengthening mode of Ni-Ni₃Si eutectic composites

Microstructure evolution of the Ni-11.5 wt%Si eutectic alloy during the melting and cooling process was elaborately examined using a high-temperature confocal laser scanning microscope (HT-CLSM). The thermal stability of the phase composition within the Ni-11.5 wt%Si eutectic alloy was thoroughly analyzed. The intricate mechanism governing the solidification of the Ni-11.5 wt%Si eutectic alloy, along with the formation of the metastable Ni₃₁Si₁₂ phase under varying cooling rates, was systematically investigated. Through in-depth in-situ observations, a well-defined heat treatment procedure was developed for Ni-Ni₃Si eutectic composites. Remarkably, the metastable Ni₃₁Si₁₂ phase can completely transform into Ni₃Si upon undergoing the prescribed heat treatment, yielding a refined lamellar structure. This structural refinement notably results in substantial enhancements in the compressive properties and fracture toughness of the Ni-Ni₃Si eutectic composite at ambient temperatures.