Page 271 - Mechanical Engineer's Data Handbook

ENGINEERING MATERIALS 259

6.18 Ceramics

Aimmimum oxide (alumina)

% Al,O,

75 86-94 94-98 > 98
Density (kgmW3) 3200 3300 3500 3700
Hardness (Moh scale) 8.5 9.0 9.0 9.0
Compressive strength (N mm-2) 1250 1750 1750 1750
Flexural strength (Nmm-2) 270 290 350 380
Max. working temperature (“C) 800 1100 1500 1600

Reaction sintered Hot pressed

Density (kgm-,) 2 300-2 600 3 120-3 180
Open porosity (YO) 18-28 0.1
Hardness (Moh scale) 9 9
Young’s modulus (N mrnw2) 160000 290000
Flexural strength (Nmm-2)
at 20°C 110-175 550-680
at 1200 “C 210 350-480

6.19 Cermets

Cermets consist of powdered ceramic material in a hard, strong, yet tough, combination; the process
matrix of metal, combining the hardness and strength involves compaction and sintering.
of ceramic with the ductility of the metal to produce a

Ceramic Matrix Applications

Tungsten carbide Cobalt } Cutting-tool bits
Titanium carbide Molybdenum, cobalt or tungsten
Molybdenum carbide Cobalt }
Silicon carbide Cobalt or chromium Dies