Strengthening of nickel-based hybrid composites processed by spark plasma sintering, high-pressure torsion, and post-deformation annealing

Nickel-based composites reinforced with nanosized and hybrid micro-/nanosized silicon carbide particles were fabricated using a processing route combining high-energy ball milling, spark plasma sintering (SPS), high-pressure torsion (HPT), and post-deformation annealing. The aim of this study was to establish the relationships between processing, microstructural evolution, and mechanical performance in Ni–SiC composites subjected to severe plastic deformation and subsequent heat treatment. Spark plasma sintering produced highly densified composites with a homogeneous distribution of the ceramic reinforcement and a refined nickel matrix. Detailed microstructural characterization revealed significant chemical and morphological evolution of the SiC reinforcement during SPS, including the formation of carbon-enriched shells around microsized particles and Ni–Si reaction products associated with nanosized reinforcement. High-pressure torsion resulted in a homogeneous ultrafine-grained microstructure accompanied by extensive grain refinement, fragmentation of microsized SiC particles, and redistribution of nanosized reinforcement throughout the matrix. These microstructural changes produced a substantial increase in hardness and tensile strength, but at the expense of tensile ductility after HPT. The Ni–hybridSiC composite achieved a tensile strength of 1526 MPa and an average microhardness of 720 HV after annealing at 300 °C, while its ultimate elongation remained approximately 0.59%. Thus, the principal mechanical benefit of the applied processing route is the development of ultrahigh strength and hardness rather than a balanced strength–ductility response. Among all investigated materials, the hybrid micro-/nano-SiC composite exhibited the most effective strengthening response, demonstrating the synergistic effect of bimodal reinforcement and severe plastic deformation on the development of ultrahigh-strength nickel-based composites.