D AY 21: C ERAMICS Inorganic & Nonmetallic. Compounds between metallic and non-metallic elements Traditional: Clay based bricks, tiles, china, porcelain, and glasses Engineering: High tech materials useful in high strength applications, take advantage of the unique properties

N ATURE OF C ERAMICS Bonding is ionic and covalent mix. These are extremely strong bonds. This leads to high melting point, high strength and high modulus of elasticity. Crystallinity is complex. Different sizes of atoms. Charge conservation. This makes slip, so common in metallic crystals, practically impossible. Also leads to less efficient packing, and lower density.

G OOD P ROPERTIES Strength and Hardness High Temperature Resistance Resistance to Corrosion Low Density

C HALLENGE Brittleness. The problem is that these materials have ductility, fracture toughness, and great flaw sensitivity. BUT, we know that it is possible to use brittle materials, provided that we do so in an intelligent way.

W HY U SE C ERAMICS FOR S TRUCTURAL A PPLICATIONS, I.E. T URBOCHARGER R OTOR ? High temperature resistance (hot exhaust gases) Low coefficient of thermal expansion (small blade tip clearance) Low mass (low polar moment of inertia for fast spin up) Durability (survive over 100,000 miles) Low cost (need willing purchasers)

Table 1.1 Turbocharger Rotor Materials (data from Callister) PropertySilicon Nitride Nickel Alloy Specific Gravity Fracture Stress (avg. at 1100 K) Weibull Modulus 10-20>50 Young's Modulus (GPa) Toughness, K IC (MPa  m) Thermal Coef. of Exp. (cm/cm per  C) 3.113

Figure 1.2 Comparison of wide-open throttle acceleration for ceramic and metal turbocharger rotors, 2.3 liter engine - Zephyr test vehicle. (Wachtman, 1989)

O VERVIEW OF A DVANTAGES OF C ERAMICS temperature resistance high hardness low density corrosion resistance

S PECIAL D ESIGN C ONSIDERATIONS FOR C ERAMICS brittleness difficulty of manufacture.