Mechanical properties and microstructure of annealed Ni/CrC-NiCr metal matrix composite prepared by cold sprayed deposition

This study investigates the effects of low (700 °C) and high (1000 °C) temperature annealing on the microstructure and mechanical properties of two metal matrix composites consisting of Ni and two separate compositions of CrC-NiCr cold-sprayed onto A-514 structure steel. The mechanical properties, including tensile strength, ductility, interface shear strength, and microhardness, were evaluated after heat treatments. Additionally, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to characterize the microstructure of the annealed deposits. The results showed that annealing significantly enhanced the inter-splat bonding quality between the matrix (nickel) particles. However, higher temperature annealing led to an increase in voids surrounding the cermet particle due to enhanced elemental diffusion. Furthermore, the interparticle bonding between the nickel particles in the matrix and the cermet particle was also improved after annealing. Depending on the composition, the ultimate tensile strength increased by a minimum of 32%, and the adhesion shear strength improved by over 77% following annealing at 1000 °C. Recrystallization and reduction of the dislocation density in the nickel matrix occurred within the splats during annealing, resulting in increased ductility from less than 0.2% in the as-sprayed condition to more than 6.5% after annealing. However, a general reduction in hardness was observed after annealing. The interplay between the annealing temperature, microstructural evolution, and mechanical performance demonstrates that the improved bonding directly influenced the mechanical properties, resulting in increased tensile strength, greater ductility, and a shift from brittle to ductile fracture behavior as the microstructure evolved.