1. 7. Ceramic Matrix Composites Ceramic matrials strenth, stiffness temperature chemical inertness low density sensitive flaw thermal shock Ceramic matrix composites → CMC is low on the ratio of fiber and matrix 1. Fabrication of CMC The matrix powder particle smaller than the fiber diameter ! Powder size, temp, pressure are parameter that Control the matrix prosity Porosity !!

2. Melt infiltration, in situ chemical reaction, and sol-gel and polymer pyrolysis are the other techniques That have been used to produced Chemical vapor infiltration (CVI) Chemical vapor deposition (CVD) → low stress → low temp Sol-gel & polymer pyrosis technique process combines thermal gradient & and pressure gradient approaches → lower temp, greater homogeneity in single-phase matrix, potential of unique multiphase matrix materials 2. properties of CMC The ratio E f /E m determines the extent of matrix microcracking → ceramic matrix fracture strain tend to be rather low strongly bonded CMC- fiber & matrix would fail at matrix failure train weakly bonded CMC- the fibers will be bridging the matrix blocks But a weaker interface, would lead to fiber-bridging of matrix microcracks. High matrix mouldus composites, matrix cracking would occur at much lower stress.

3. fiber length ( the fiber ratio[ length/diameter]), fiber orientation, strength & moduli of fiber & matrix, Thermal mismatch, matrix porosity, fiber flaw – factor of CMC process ! aligned continuous fibers do lead to a real fiber reinforcement effect ! Stress at fiber ends is minimized and higher fiber volume fractions can be obtained but it becomes Difficult to remove matrix porosity 3. Interface in CMC Δ  =  f -  m  - linear expansion coefficients Δ  (+) – the matrix is compressed on cooling – good ! Δ  (-) – the matrix is tensioned on cooling – matrix cracking -In the radial direction Δ  (+) – the fiber tend to shrink away from the matrix on cooling Δ  (+) – the fiber and matrix bond strength can even be improved. Matrix cracking resulting from thermal mismatch is a more serious problem in short-fiber composites ▶ short-fiber composite owing to increase stress at the fiber ends, matrix cracking occurs in all direction ▶ thus, the composite is very weak !

4. chemical compatibility between matrix and the fiber – zirconia reinforced magnesia composite system → heat treatment is improved bonding ! Mechanical bonding chemical bonding 4. Toughness of CMC Fibers can play the role of toughening agents in ceramic matrices → tensile stress increases from a minium ar both fiber Ends and attains a maxium along the central portion Of the fiber

5. Use of a volume fraction of fiber →stiffer than matrix →needed to produce matrix microcracking → higher composite ultimate tensile stress as well as a high creep resistance ! →A high volume fraction and a small fiber diameter also provide a sufficient number of fibers for crack bridging and postpone Crack propagation to higher strain levels 5. applications of CMC heat engines, special electronic/electrical applications, energy conversion, military system.. Commercial application of CMC is in cutting tools