Effect of MoSi2-Si3N4/SiC Multi-Layer Coating on the Oxidation Resistance of Carbon/Carbon Composites above 1770 K

Imran Abbas,Mudaser Ullah,Hassan Elahi,Muhammad Ali Siddiqui,Faisal Qayyum,Yanxiang Wang

doi:10.3390/jcs4030086

Abstract

To improve the oxidation resistance of carbon/carbon composites at high temperatures (>1770 K), they were coated with MoSi2-Si3N4/SiC. The slurry and pack cementation methods were adopted to deposit the inner SiC layer and outer MoSi2-Si3N4 layer. The phase composition, microstructure, and elemental distributions in the coating were analyzed using SEM, XRD, EDS, and Raman spectroscopy. Oxidation tests show that the deposited multi-layer coating can protect the carbon/carbon matrix from oxidation at high temperatures (>1770 K) for 150h and that the coating can withstand 40 thermal cycles between 1773 and 300 K. It is observed that Si3N4 assists in the formation of a dense SiO2 layer at a high temperature, which plays a vital role in increasing the thermal cyclic and oxidation resistance of the coating itself. The weight loss of coated carbon/carbon composite is attributed to the formation of micro-cracks and diffusion of SiO2, MoO3, and N2 out of the material at high temperatures.

Highlights

For aggressive service environments in the nuclear and aerospace industry, carbon/carbon composites are candidate structural materials due to their attractive properties such as a high strength-to-weight ratio, thermal cyclic oxidation resistance, strength retention, and a low thermal expansion coefficient [1,2,3,4,5]
The mismatch between the coefficient of thermal expansion (CTE) of the outer MoSi2 layer and the inner SiC-coated carbon/carbon matrix causes the degradation of the coating under thermal cycling and lowers the coating durability [15,16]
The carbon/carbon composite used in this study was carbon fiber-strengthened graphite

Summary

Introduction

For aggressive service environments in the nuclear and aerospace industry, carbon/carbon composites are candidate structural materials due to their attractive properties such as a high strength-to-weight ratio, thermal cyclic oxidation resistance, strength retention, and a low thermal expansion coefficient [1,2,3,4,5]. These composites exhibit limitations such as susceptibility to oxidation beyond 773 K and strength loss upon exposure to high temperatures. The mismatch between the CTEs of the outer MoSi2 layer and the inner SiC-coated carbon/carbon matrix causes the degradation of the coating under thermal cycling and lowers the coating durability [15,16]

Methods

Results

Conclusion