Ablation behaviour and mechanical performance of ZrB2-ZrC-SiC modified carbon/carbon composites prepared by vacuum infiltration combined with reactive melt infiltration

Abstract

The development of advanced aircraft relies on high performance thermal-structural materials, and carbon/carbon composites (C/C) composited with ultrahigh-temperature ceramics are ideal candidates. However, the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix. Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi2, C/C-ZrB2-ZrC-SiC composites prepared by the vacuum infiltration of ZrB2 combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases. The mass and linear ablation rates of the C/C-ZrB2-ZrC-SiC composites were respectively 68.9% and 29.7% lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration. The ablation performance was improved because the volatilization of B2O3, removes some of the heat, and the more uniformly distributed ZrO2, that helps produce a ZrO2-SiO2 continuous protective layer, hinders oxygen infiltration and decreases ablation.

1. Introduction

In recent years, the development of advanced aircraft has set high requirements for the performance of thermal-structural materials. Carbon/carbon (C/C) composites have been utilized extensively in the aerospace field because of their exceptional characteristics, including low density, high specific strength and superior thermal shock resistance. However, oxidation of C/C composites occurs at 400 °C, and the corresponding oxidation rate increases rapidly as the temperature rises, severely limiting their applications. Therefore, enhancing the anti-oxidation performance of C/C composites is of great significance.

Ultra-high temperature ceramics (UHTCs) have high melting points and exceptional oxidation/ablation resistance properties, showing considerable potential for applications in extreme aerodynamic heating conditions. However, considering their intrinsic brittleness along with poor thermal shock resistance, bulk UHTCs are prone to catastrophic failure. The combination of C/C and UHTCs to fabricate C/C-UHTCs could mitigate their respective limitations. ZrC and ZrB2 as the typical representatives of the family of UHTCs, have high melting points, good high-temperature stabilities and relatively low costs. The combination of SiC can further improve their resistance to oxidation in a broad temperature range. As a result, many methods have been developed to prepare C/C-ZrB2-ZrC-SiC composites, such as precursor infiltration and pyrolysis (PIP), reactive melt infiltration (RMI) and slurry impregnation (SI). The main advantage of PIP is that variable ceramics can be introduced into C/C composites through the adjustment of the precursors. However, it is time-consuming because of the repeated infiltration-pyrolysis cycles. Differing from PIP, RMI represents the infiltration of C/C composites with molten metal, which is a cost-effective and time-saving method for fabricating dense C/C-ZrC-ZrB2-SiC composites. However, the reaction between the molten metal with the matrix and the contents of the ceramics is difficult to control, which necessitates combination with other methods. SI is a simple way to introduce ceramics into C/C composites without damage, but its efficiency is low and the compactness of the obtained composites is poor. Compared with the traditional SI, vacuum filtration is expected to have a higher introduction efficiency and short preparation cycle driven by the pumping force. Additionally, the amounts of the introduced ceramics are controllable, which could make up for the shortcomings of RMI. So far, there are few works reported concerning the combination of vacuum filtration and RMI to prepare the C/C-ZrC-ZrB2-SiC composites.

In this work, ZrB2 was firstly introduced into C/C composites by vacuum filtration, and the composites were densified subsequently by RMI ZrSi2 to obtain C/C-ZrC-ZrB2-SiC composites. The influence of ZrB2 on mechanical properties and ablation performance of the C/C-ZrC-ZrB2-SiC composites were investigated, and the associated ablation mechanism was elucidated.