Effect of incorporation of hafnium diboride nanofibers on thermomechanical properties of carbon fiber–phenolic composites.

Carbon fiber/phenolic (C/Ph) composites were modified with different weight ratios of hafnium diboride (HfB2) nanofibers to apperceive thermomechanical properties of C/Ph–Hf nanocomposites. Mechanical properties, thermal stability, and ablation resistance of C/Ph–Hf nanocomposites were found to be optimum when the weight percentage of HfB2 was equal to one. Maximum flexural strength and modulus were obtained with 118 MPa and 1.9 GPa for C/Ph–1%Hf nanocomposite, respectively. Increasing the proportion of HfB2, by delaying the temperature of thermal degradation of nanocomposites, enhanced the thermal stability and residual of C/Ph–Hf relative to C/Ph in both nitrogen and air environments. In the oxyacetylene flame test at 2500°C for 160 s, the optimum mass ablation rate of C/Ph–1%Hf nanocomposites was found to be 0.0150 g/s compared to 0.068 g/s for blank C/Ph, along with reducing the back surface temperature by 51%. The ablation mechanism of C/Ph–Hf nanocomposites after the oxyacetylene torch test was concluded from the derivations obtained from X‐ray diffraction, energy dispersion spectroscopy, and microstructure analyses. These clarified that the formation of high‐temperature species, such as HfO2, HfC, and B4C owing to oxidation of HfB2 and subsequent reaction products with char, resulted in an increased ablation resistance of the nanocomposites. [ABSTRACT FROM AUTHOR]