BN/SiC coating

Typical stress-strain curves, recorded in 3-point flexure, for the uncoated and BN/SiC coated fiber-reinforced composites [33-34] are shown in Fig. 12. Also shown for comparison is the stress-strain curve for a hotpressed BSAS monolith. The monolith shows bend strength of 130 MPa, modulus of 98 GPa and fails in brittle mode, as expected. The uncoated fiber-reinforced CMC shows a monolithic-like failure with strength of -200 MPa and failure strain of 0.1 %. This shows that reinforcement of BSAS matrix with uncoated Hi-Nicalon fibers does not yield a strong or tough material. This may indicate a strong bond between the uncoated fibers and the matrix. However, fiber push-in and push-out tests [33, 35]... 

FIGURE 12. Stress-strain curves for unidirectional uncoated and BN/SiC-coated Hi-Nicalon/BSAS composites recorded in 3-point flexure also shown is the curve for hot pressed monolithic BSAS. 

Tensile properties of unidirectional BN/SiC coated Hi-Nicalon fiber reinforced celsian matrix composites [36-37] from room temperature to 1200°C in air are shown in Table 6, The value of Young s modulus decreased with increase in test temperature indicating the presence of glassy phase in the matrix. The yield stress decreased from room temperature... 

Ha. J.S. and Chawla, K.K. (1993). Effect of SiC/BN double coating on fiber pullout on mullite fiber/ mullitc matrix composites. J. Mater. Sci. Lett. 12, 84-86. 

Sun, E.Y., Nutt, S.R. and Brennan, J.J. (1994). Interfacial microstructure and chemistry of SiC/BN dual-coated Nicalon-fiber reinforced glass-ceramic matrix composites. J. Am. Ceram. Soc. 77, 1329-1239. 

E. Y. Sun, S. R. Nutt, and J. J. Brennan, Interfacial Microstructure and Chemistry of SiC/BN Dual-Coated Nicalon Fiber Reinforced Glass-Ceramic Matrix Composites, J. Am. Ceram. Soc., 77[5], 1329-1339 (1994). 

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