Temperature-dependent evolution of interfacial zones in SiC_f/C/Ti17 composites

Abstract

Schematic representation of the fabrication process for SiCf/C/Ti17 by MCF method.

Optimization of C/TiC duplex diffusion barrier coatings for SiC /Ti composites based on interfacial structure evolution exploration

“…5a and 5b shown, in contrast to as-deposited SiCf/C/QC-TiC/Ti17 composite, the TiCx grains in close proximity to the carbon coating have grown and coarsened from the original ~50 nm to 200~300 nm after heat treatment, which can be understood as the original fine-grained TiCx layer having disappeared and a new ~400 nm thick transition-grained TiCx layer formed. This is analogous to the microstructural evolution of a C single coating system after heat treatment at 1100°C for 2 hr [10].…”

“…TiC [3,9], TiBx [9,11,12,13], B4C [14,15] and Mo [16] are being investigated, along with inner carbon coatings which form C/X (X represents the outer protective coating) duplex coatings at high temperatures. For instance, the inter-diffusion and reaction of Ti/SiC can be effectively inhibited using TiB2 protective coatings [9,10], (especially 0.2 μm TiB2 at the in-service temperature of 820 °C) which shows no apparent interfacial reactions up to 1000 °C [9]. However, B-rich TiB2 reacts with Ti to form needle/rodlike TiB, which grows rapidly and reduces the effectiveness of the diffusion barrier as the temperature increases further [17,18,19].…”

“…Considering the interfacial reaction mechanism, the interfacial reaction occurs when C diffuses into the Ti matrix and reacts with the α-Ti/β-Ti phase [10,26], while there is hardly C diffusion through the existing QC-TiC layer due to obstruction by the quasi-stoichiometric coarse-grained TiCx layer. As such, larger coarse grained (＞500 nm) quasi-stoichiometric TiCx in the SiCf/C/QC-TiC/Ti17 composite should more effectively inhibit C diffusion than the coarse-grained (＞100 nm) sub-stoichiometric TiCx in SiCf/C/Ti17 composite.…”

“…Until now, carbon coatings have been comprehensively employed as a reaction barrier coating to protect the SiC fibre and minimise interfacial reactions [6,9]. It has been confirmed that carbon coatings, and the TiC interfacial reaction layer perform well during fabrication and in-service at low temperature (< 800°C) [10]. However, carbon itself is not a thermo-chemical barrier layer as it reacts with Ti (Ti + C →TiC, 950°C, ΔG=-170 kJ/mol [9]) and hence is rapidly depleted.…”

“…1100°C), even over a relatively short period of time (e.g. 2 hrs) [10]. Therefore, new coating systems are needed for demanding, high temperature applications such as hypersonic flight vehicles.…”