Role of carbon nanotubes on mechanical properties of SiC-B4C-Ni hybrid composites fabricated by reactive spark plasma sintering

The present study was conducted to investigate the microstructural and mechanical properties of SiC-45 vol%B₄C-10 vol%Ni and SiC-45 vol% B₄C-10 vol%Ni-5vol% CNT in-situ composites fabricated through reactive spark plasma sintering (SPS) method at 1650 °C for 5 min. The phase and microstructural characterization of the composites were evaluated utilizing x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Ultimately, microhardness, flexural strength, and fracture toughness of the composites were measured. Densification behavior of the samples revealed that the initial shrinkage of the composites took place at about 750 °C, which is related to the reaction between Ni and SiC phases. XRD results confirmed the formation of Ni₂Si phase. The relative density of 98.3 ± 0.32% was achieved for the SiC-B₄C-10Ni sample; this value was 97.8 ± 0.62% for the SiC-B₄C-10Ni-5CNT sample. The flexural strength of 362 ± 23 MPa was achieved for the SiC-B₄C-10Ni sample; this value was 369 ± 15 MPa for the SiC-B₄C-10Ni-5CNT sample. The comparison between the fabricated composites concerning the fracture toughness indicated further fracture toughness of the SiC-B₄C-10Ni-5CNT sample (5.82 ± 0.32 MPa m^1/2) than that of the SiC-B₄C-10Ni sample (3.35 ± 0.56 MPa m^1/2). Formation of micro-cracks, crack path deflection, and CNT bridging was the main toughening mechanisms in the SiC-B₄C-10Ni-5CNT sample.