Composite microstructures, thermal ceramics

FIGURE 12.11 Improvements of the mechanical properties of three-dimensional reinforced CMCs by hybrid infiltration routes (a) R.T. flexural stress-strain plots for a three-dimensional carbon fiber reinforced composite before and after cycles of infiltration (comparison between eight cycles with zirconium propoxide and fonr cycles pins a last infiltration with aluminum-silicon ester (b) plot of the mechanical strength as a fnnction of the final open porosity for composites and matrix of equivalent porosity, before and after infiltration (Reprinted from Colomban, R and Wey, M., Sol-gel control of the matrix net-shape sintering in 3D reinforced ceramic matrix composites, J. Eur. Ceram. Soc., 17, 1475, 1997. With permission from Elsevier) (c) R.T. tensile behavior (d) comparison of the R.T. mechanical strength after thermal treatments at various temperatures. (Reprinted from Colomban, R, Tailoring of the nano/microstructure of heterogeneous ceramics by sol-gel routes, Ceram. Trans., 95, 243, 1998. With permission from The American Ceramic Society.)... 

Apart from their thermal stability a number of other factors are important in the choice of refractory materials e.g. thermal expansion coefficient, thermal shock resistance, chemical resistance, thermal conductivity and abrasion resistance. These properties depend upon both the microstructure and composition of the ceramic material. 

C. Labrugere, L. Guillaumat, A. Guette and R. Naslain, Mechanical and Microstructural Change in 0-90° SiC/MAS-L Composites after Thermal Ageing Vacuum, Ar and CO Atmosphere, J. Europ. Ceram. Soc. 19,... 

Ziegler G, Lucke J, Richter I, Suttor D, C-fibre reinforced composites with pol5nner-deiived matrix, microstructure, thermal properties, strength, Baxter J, Cot L, Fordham R, Gabis V, Hellot Y, Lefebvre M, Le Doussal H, Le Sech A, Naslain R, Sevagen A eds., European Ceramic Society, Euro Ceramics V, Part 3. Trans Tech Publications, Switzerland, 1870-1873, 1997 Key Eng Mater, 132-136. 

As with other ceramic composites, the combination of a- and/or P-sialon with reinforcement agents results in sialon composites. This simple and obvious statement encompasses many factors which must be taken into account for successfully fabricating composites with a designed microstructure and improved properties (Prewo, 1989). For sialon matrix composites, the most important factors are physical compatibility including Young s modulus, elastic strain (Kerans and Parthasarathy, 1991) and thermal expansion coefficient (Sambell etal., 1972a, b), and chemical compatibility between sialon matrix... 

Functionally graded materials (FGMs) are multifunctional materials, which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling variations in thermal, structural or functional properties. Also in the ceramics composites field, a wide range of functionally graded (FG) ceramics are available. Hence, a possible classification of the different classes is made in this chapter. 

The substrates carrying the circuits shown in Fig. 4.5 are a 95-96% alumina. This ceramic has been adopted for its combination of physical and chemical characteristics and, importantly, low cost. It offers a combination of mechanical, thermal and electrical properties which meet the in-service requirements, and compositional and microstructural characteristics suited to thick film printing (see Section 4.2.2). Alumina substrates are manufactured on a very large scale making the unit costs a small fraction of the total circuit cost. 

Fig. 8.15 Changes in interface microstructure in SiC fiber-reinforced BMAS glass-ceramic composites induced by exposure to high temperature oxidizing environments, (a) After tensile stress-rupture experiment at 1100°C, the 90° fibers show a distinct dual layer at the BN coating-fiber interface, (b) After thermal aging for 500 h at 1200°C, a subtle double layer appears at the same site, (c) Near the composite surface, the effects of thermal aging (and oxidation) are more pronounced.24...

Ananthakumar S., Jayasankar M., Warrier K.G.K.. Microstructural, mechanical and thermal characterisation of sol-gel derived aluminium titanate-mullite ceramic composites. Acta Materialia, 2006,54 2965-2973... 

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