Effect of BNNTs/matrix interface tailoring on toughness and fracture morphology of hierarchical SiCf/SiC composites

Guangxiang Zhu,Qian Feng,Jinshan Yang,Hongda Wang,Qingliang Shan,Shaoming Dong,Yudong Xue,Jianbao Hu

doi:10.1007/s40145-019-0338-0

Abstract

A thin BN interphase is applied on BNNTs surface to tailor the interfacial bonding between BNNTs and SiC matrix in hierarchical SiCf/SiC composites. The thickness of BN interphase ranging from 10 to 70 nm can be optimized by chemical vapor deposition after BNNTs are in situ grown on SiC fiber surface. Without BN interphase, the fracture toughness of hierarchical SiCf/SiC composites can be impaired by 13.6% due to strong interfacial bonding. As long as BN interphase with 30–45 nm thickness is applied, the interfacial bonding can be optimized and fracture toughness of hierarchical composites can be improved by 27.3%. It implies that tailoring BNNTs/matrix interface by depositing a layer of BN interphase is in favor of activating energy dissipation mechanisms at nanoscale induced by BNNTs.

Highlights

Since the first prediction in 1994 and experimentally synthesis in the following year, boron nitride nanotubes (BNNTs) have attracted significant attention from scientists due to their remarkable properties [1]
BN-coated BNNTs reinforced hierarchical SiCf/SiC composites were fabricated by two steps: firstly in situ growing BNNTs on SiC fiber surface, which can be found in detail in our previous study [10], and subsequently matrix densification via polymer impregnation/pyrolysis (PIP) and chemical vapor infiltration (CVI) method. (PyC/SiC)n (n = 3) multilayer interphase was deposited on SiC fiber cloths before the in situ growth of BNNTs
After the deposition of BN interphase, the surface of BNNTs becomes rough and the morphology of the bubblechain tube walls cannot be observed from scanning electron microscope (SEM) pictures

Summary

Introduction

Since the first prediction in 1994 and experimentally synthesis in the following year, boron nitride nanotubes (BNNTs) have attracted significant attention from scientists due to their remarkable properties [1]. A proper interfacial bonding is the key factor to obtain excellent mechanical properties and energy dissipation mechanisms for a composite system, which can lead to reinforcement pull-out for better toughness [5,7]. For a brittle matrix like ceramic, it demands the interface weak enough to allow debonding, sliding, and pull-out of nanotubes. In this case, energy dissipation, as well as toughening in matrix, can be aroused [5,7]. The interphase, which is defined as a thin-layer material with low shear strength, is usually used in micro-scale fiber reinforced composites to control the fiber/matrix interfacial bonding [8,9]. Toughening mechanisms of BNNTs/matrix interface tailoring are discussed based on the investigation

Experimental procedures

Results

Discussions

Conclusions