and silicon nitride, processes of abnormal grain growth may result in a microstructure exhibiting elongated large grains in a matrix of finer rounded grains. AGG derived microstructures exhibit toughening due to crack bridging and crack deflection by the elongated grains, which can be considered as an in-situ produced fibre reinforcement. Recently Ultra-high temperature ceramics (UHTCs) were investigated as ceramic matrix in a new class of CMC so-called Ultra-high Temperature Ceramic Matrix Composites (UHTCMC) or Ultra-high Temperature Ceramic Composites (UHTCC). Generally, CMC names include a combination of type of fiber/type of matrix. For example, C/C stands for carbon-fiber-reinforced carbon (carbon/carbon), or C/SiC for carbon-fiber-reinforced silicon carbide. Sometimes the manufacturing process is included, and a C/SiC composite manufactured with the liquid polymer infiltration (LPI) process (see below) is abbreviated as LPI-C/SiC. The important commercially available CMCs are C/C, C/SiC, SiC/SiC and . They differ from conventional ceramics in the following properties, presented in more detail below: Elongation to rupture up to 1% Strongly increased fracture toughness Extreme thermal shock resistance Improved dynamical load capability Anisotropic properties following the orientation of fibers Manufacture The manufacturing processes usually consist of the following three steps: Lay-up and fixation of the fibers, shaped like the desired component Infiltration of the matrix material Final machining and, if required, further treatments like coating or impregnation of the intrinsic porosity. The first and the last step are almost the same for all CMCs: In step one, the fibers, often named rovings, are arranged and fixed using techniques used in fiber-reinforced plastic materials, such as lay-up of fabrics, filament winding, braiding and knotting. The result of this procedure is called fiber-preform or simply preform. For the second step, five different procedures are used to fill the ceramic matrix in between the fibers of the preform: Deposition out of a gas mixture Pyrolysis of a pre-ceramic polymer Chemical reaction of elements Sintering at a relatively low temperature in the range Electrophoretic deposition of a ceramic powder Procedures one, two and three find applications with non-oxide CMCs, whereas the fourth one is used for oxide CMCs; combinations of these procedures are also practiced. The fifth procedure is not yet established in industrial processes. All procedures have sub-variations, which differ in technical details. All procedures yield a porous material. The third and final step of machining – grinding, drilling, lapping or milling – has to be done with diamond tools. CMCs can also