Nathan Sutemire1,2,Micheal Rix2,Stephen Kyle-Henney2,Mark Baker1,Mark Whiting1
University of Surrey1,TISICS Ltd.2
Nathan Sutemire1,2,Micheal Rix2,Stephen Kyle-Henney2,Mark Baker1,Mark Whiting1
University of Surrey1,TISICS Ltd.2
SiC monofilament reinforced titanium MMCs offer dramatic weight savings and improved mechanical performance at elevated temperatures, compared to monolithic aerospace alloys<sup>1</sup>. Their implementation in aerospace applications will enable significant reductions in CO<sub>2</sub> emissions.<br/>UK based company, TISICS, manufactures a 140 µm diameter SiC monofilament (SM3256) via a high-speed chemical vapour deposition (CVD) process<sup>2</sup>. These monofilaments consist of stoichiometric SiC deposited onto a 15 µm diameter W core, with a bilayer coating deposited on top containing: an inner SiC<sub>x</sub> layer, and an outer amorphous C layer. The exceptional mechanical properties, narrow strength distribution, and the reinforcing performance of the coated fibres in composites of SM3256 is dependent on the complex microstructures, more precisely at the interfaces between the sub-components, present in the monofilament.<br/>At loads exceeding the expected composite performance, it is desirable that the fracture of the monofilaments initiates at the SiC/W reaction zone (at the interface between the SiC and W core). Furthermore, the activation of the toughening mechanisms in composites requires the debonding of the coating layers to arrest crack propagation.<br/>In this presentation, we investigate the interfaces within SM3256 that are critical to its performance. Complimentary use of Tip Enhanced Raman Spectroscopy (TERS), HRTEM, SEM and confocal Raman spectroscopy were employed to explore the complex microstructures and phases within the SiC bulk and its interfaces. Investigation of the SiC<sub>x</sub> coating using TERS and HRTEM enabled amorphous and crystalline nanostructures within the sub-micrometre coating layer to be analysed at nanoscale resolution for the first time. In the SiC-W reaction zone, distinct phases together with nano-voids were observed and examined in detail using SEM and HRTEM. The nano-voids could be acting as fracture initiation sites.<br/><u><b>References</b></u><br/>1. Rahman, K. M., Vorontsov, V. A., Flitcroft, S. M. & Dye, D. A High Strength Ti–SiC Metal Matrix Composite. <i>Advanced Engineering Materials</i> <b>19</b>, (2017).<br/>2. Rix, M. v., Baker, M., Whiting, M. J., Durman, R. P. & Shatwell, R. A. An improved silicon carbide monofilament for the reinforcement of metal matrix composites. <i>Minerals, Metals and Materials Series</i> 317–324 (2017).