Microstructure evolution and mechanical properties of TC4/Ni metallic-intermetallic laminated composites: Formation and strengthening effects of Ti2Ni phases

TC4/Ni metallic-intermetallic laminated (TN-MIL) composites were prepared by hot pressing at different temperatures and with varying Ni foils thicknesses. The phase formation and Ti2Ni microstructure evolution were analyzed in detail using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and x-ray diffraction (XRD). The mechanical properties were evaluated through nanoindentation, room-temperature compression, and tensile tests, while fracture morphology was examined by SEM. The results show that as the hot-pressing temperature increases, the Ni3Ti and TiNi phases at the interface gradually transform into the Ti2Ni phase. Once the Ni is fully dissolved in the TC4 matrix, the intermetallic compound layer disappears. This diffusion process creates a concentration gradient in TC4. As the Ni concentration increases, the Ti2Ni phase transitions from an island-like structure to a network, and ultimately forms a lamellar or mixed morphology. The TN-MIL composite prepared at 800 degrees C has three intermetallic compound layers of Ni3Ti, TiNi and Ti2Ni, as well as lamellar, network and island-like Ti2Ni structures in the TC4 matrix. This composite demonstrates excellent mechanical performance, achieving a maximum compressive strength of 1580 MPa and an ultimate tensile strength of 1010 MPa. The Ti2Ni phase improves the material's deformation resistance due to its high strength and hardness, thereby increasing the overall hardness and strength. However, the inherent brittleness of Ti2Ni and its propensity to induce stress concentrations at grain boundaries under strain conditions significantly elevate the risk of material fracture.