High-temperature mechanical performances of SiC whisker in-situ toughened 3DN C/SiC countersunk bolts prepared by chemical vapor infiltration

High performance bolts, made of continuous fiber reinforced silicon carbide composites (C/SiC), are crucial to the design and preparation of the hot-end C/SiC components with large complex structures both in aerospace and aeronautical fields. In this work, in-situ grown SiC whiskers were uniformly introduced into the porous laminated 3DN C/SiC countersunk bolt, in order to improve the brittle nature of the 3DN C/SiC threads. Results showed that 7 % increase of tensile strength of the 3DN C/SiC countersunk bolts was achieved via in-situ grown SiC whiskers, and a fatigue life of 10⁶ cycles was also passed. The stud fracture morphologies indicated that the SiC whiskers grew within the woven pores and toughened the layered SiC matrix, so that the load transfer between the layered SiC matrix and carbon fibers was improved under tension. Further high temperature tests showed that the tensile and the shear strengths of the in-situ toughened 3DN C/SiC countersunk bolts were degraded to 64.74 % and 28.83 % at 1000 °C in air respectively. During the thermal exposure, the carbon fibers were largely consumed by oxidation, while the SiC whiskers grew slender and formed a fluffy layer to partially reinforce the SiC matrix. The synergy effect of SiC whiskers and carbon fibers to hinder crack propagation and to toughen the SiC matrix contributes to the above mechanical properties of the bolts.