Effect of Multi-walled Carbon Nanotubes on Material Properties of Spark Plasma Sintered Silicon Nitride-Based Advanced Ceramic Composites

The aim of the present investigation is to develop advanced silicon nitride (Si₃N₄) ceramic composites reinforced with multi-walled carbon nanotubes (MWCNTs) to achieve optimal material properties. Magnesium oxide (MgO) and yttrium oxide (Y₂O₃) were employed as sintering aids in the synthesis of MWCNT-reinforced Si₃N₄ composites. Fabrication was performed using spark plasma sintering at 1600 °C with a heating rate of 100 °C/min, a pressure of 50 MPa, and a holding time of 5 minutes. Identical parameters were used to fabricate composites with varying weight ratios of Si₃N₄, sintering aids, and MWCNTs. The samples were characterized for phase transformation, crystalline phase identification, microstructure, and elemental composition using x-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, electron probe microanalysis, and wavelength dispersive spectroscopy. Mechanical, thermal, and tribological properties were also evaluated. The results demonstrated that Si₃N₄ composites with 1 wt.% CNT concentrations exhibited optimal mechanical (H_V = 16.6 GPa and K_IC = 6.4 MPa m^1/2), thermal (k = 59 Wm⁻¹ k⁻¹ and α = 0.11 cm²s⁻¹), and tribological properties (wear volume \(\approx\) $\approx$ 0.029 mm³, a wear rate \(\approx\) $\approx$ 4.5 × 10⁻⁸ mm³ N⁻¹ m⁻¹, and \(\mu_{{{\text{mean}}}}\) ${\mu }_{\text{mean}}$  = 0.12) due to uniform CNT dispersion in the Si₃N₄ matrix. In contrast, higher CNT concentrations (> 1 wt.%) led to a decline in material properties due to CNT agglomeration. These findings offer valuable insights for the design and optimization of advanced Si₃N₄ composites for diverse engineering applications, recognizing the delicate balance required for superior material performance.