Abstract
Reactive melt infiltration of Si-based alloys into C preforms and SiC/C composites may be an affordable alternative route to fabricate highly performant lightweighting metal matrix and ceramic matrix composites (CMCs), as well as to obtain reliable and long-term stable joints. In order to optimize reactive infiltration process and to tailor the joint microstructures, the knowledge of interfacial phenomena including thermodynamics, kinetics and surface properties of involved phases (i.e., metals and ceramics) as well as wettability and reactivity occurring between dissimilar materials is of crucial importance. In the present work, the feasibility study of a novel brazing method using Si-Ti alloys as filler for SiCf/SiC is reported and supported by the analysis of microstructural evolution and interfacial phenomena observed during the joining process. Namely, the CMC joining was successfully obtained via the reactive infiltration approach. The results obtained were critically discussed and compared with the know-how coming from the previously carried out investigations on the wetting and reactivity of Si-Ti melts in contact with glassy-C and HIP-SiC substrates. In particular, the microstructural evolution of the Si-Ti/C and Si-Ti/SiC interfaces during wetting tests and at the joint of CMC parts was analyzed and related to the operating conditions.
Highlights
Lightweight metal and ceramic matrix composites (MMCs and CMCs) reinforced by high-strength continuous ceramic fibers emerge as ideal structural materials in several applications mainly related to automotive, aircraft and aerospace industries because of their superior high-temperature strength, low density and improved damage tolerance (Ref 1)
Despite the manufacturing processes of CMCs have reached a high level of reproducibility, their use is currently limited to a great extent by the difficulties encountered in producing successfully large and complex CMCs shapes, and by their assembling and integration with dissimilar materials, i.e., metals, ceramics or other composites
The quality of the assembly has been evaluated through metallographic examinations on polished sections by optical microscopy and scanning electron microscopy (SEM)/energydispersive x-ray detectors (EDS) techniques both on the whole assembly and at the joint interfaces developed between Si-Ti alloy, SiC matrix and SiC fibers
Summary
Lightweight metal and ceramic matrix composites (MMCs and CMCs) reinforced by high-strength continuous ceramic fibers emerge as ideal structural materials in several applications mainly related to automotive, aircraft and aerospace industries because of their superior high-temperature strength, low density and improved damage tolerance (Ref 1). The feasibility study on a novel Si-16.2Ti (in at.%) eutectic alloy (hereafter indicated as Si-Ti eutectic alloy) used as a filler and the application of the above-mentioned joining/brazing technique to SiCf/SiC at T = 1350 °C under a vacuum was carried out Both the constituents exhibit excellent overall mechanical and physical properties, such as low density, hightemperature oxidation resistance (due to the growth of a stable passivating and self-healing SiO2 scale layer) and radiation resistance, making such assembling very promising in most advanced application fields involving aerospace, aviation, military and nuclear power (Ref [12,13,14]). The quality of the assembly has been evaluated through metallographic examinations on polished sections by optical microscopy and SEM/EDS techniques both on the whole assembly and at the joint interfaces developed between Si-Ti alloy, SiC matrix and SiC fibers
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