The Key Role of Ball Milling Time in the Microstructure and Mechanical Property of Ni-TiCNP Composites

Abstract

Titanium carbide nanoparticle-reinforced nickel-based alloys (Ni-TiCNP composites) with ball milling time ranging from 8 to 72 h were prepared by ball milling and spark plasma sintering. Transmission electron microscopy (TEM) and scanning electron microscopy equipped with electron backscatter diffraction were used to characterize the microstructures. Their hardness and tensile properties were measured using the Vickers pyramid method and tensile tests. TEM results showed that a slight coarsening of TiCNP occurred during the ball milling process. The grain sizes of the Ni-TiCNP composites with various ball milling times were different, but they were all much smaller than those of the pure Ni. In all cases, the Ni-TiCNP composites showed higher strengths and hardness values than the unreinforced pure nickel. Furthermore, the strength of the Ni-TiCNP composites increased initially and then decreased as a function of ball milling time. The maximum strengths occurred in the 24-h ball milling sample, which presented the lowest average grain size. The Hall-Petch strengthening was suggested to be the main reason responsible for such variations in mechanical properties. Additionally, the elongation percentage of the Ni-TiCNP composites decreased gradually with ball milling time. This may be caused by the change of microvoids in the composite as the ball milling time varies, which is also related to their fracture behavior.