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

Abstract

Carbon fiber/phenolic (C/Ph) composites were modified with different weight ratios of hafnium diboride (HfB 2 ) 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 HfB 2 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 HfB 2 , 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 HfO 2 , HfC, and B 4 C owing to oxidation of HfB 2 and subsequent reaction products with char, resulted in an increased ablation resistance of the nanocomposites.