Promotion of the mechanical properties and thermal conductivity of epoxy by low Si3N4 whisker content and its mechanisms

Si₃N₄ whisker (Si₃N_4w) is selected as epoxy filler. The influence of filler content on the bulk density, porosity, bending strength, Young's modulus, critical stress intensity factor, work of failure, morphologies of fracture surface, and thermal conductivity of Si₃N_4w/epoxy is investigated. The bending strength is 82.63 MPa at a Si₃N_4w content of 5 vol% and increases to 25.29% more than that of neat epoxy. Compared with that of neat epoxy, the work of failure and thermal conductivity increase by 455% and 34.78% to 18 248.92 J·m⁻² and 0.31 W·m⁻¹·K⁻¹, respectively, at a Si₃N_4w content of 7 vol%. However, Si₃N_4w/epoxy becomes sensitive to precrack due to a weak C N bond and residual tensile stress at the interface, thereby resulting in the decline of critical stress intensity factor. The coexistence of various energy dissipation mechanisms, namely, steps, craters or depressions, stress whitening, plastic flow, pull out of Si₃N_4w, and rough fracture surface, is observed in Si₃N_4w/epoxy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48721.