NIST Standard Reference Database 150

**Last Update to Data Content: **2002

**Reference**: "Material Properties of a Sintered alpha-SiC,"
R. G. Munro, Journal of Physical and Chemical Reference Data,
Vol. 26, pp. 1195-1203 (1997).

**Other materials**: Property Data Summaries

The data presented here were derived from reported values for a narrowly defined material specification for sintered alpha-silicon carbide in which the density is approximately (98±1) % of the density of single crystal SiC(6H) with a mean grain size of (6±2) µm. The mass fractions of boron and free carbon in the sintered composition are (0.4±0.1) % and (0.5±0.1) % respectively.

Special Notes on Properties:Data Status: Validated Crystal System: Hexagonal, 6 formula units per unit cell Nominal Grain Size: (6±2) µm Creep Characteristics in Compression in the range 100 MPa to 400 MPa: T < 1600 °C T > 1600 °C ----------- ----------- Activation energy: 442 kJ/mol 944 kJ/mol Stress exponent: 1.36 1.32 Tribology Characteristics (dry SiC on SiC): The dimensionless wear coefficient, KW, may be cited as KW = (2.5±2)x10^{-4}when the sliding speed is <= 0.3 m/s, the load is <= 10 N, and the temperature is in the range 0 °C <= T <= 1000 °C. There may be a small initial increase in KW as the temperature increases from room temperature, but the apparent increase is smaller than the uncertainty in the property value. Concurrently, the friction coefficient appears to have a value of 0.7±0.15 for T < 250 °C and 0.4±0.1 for T > 250 °C. Examinations of the microstructure suggest that the higher friction region with T < 250 °C is a result of the ploughing wear of the surface, while for T > 250 °C, the formation of mixed oxides on the surface reduce the effective coefficient of friction. When the load is increased above 10 N, however, the order of magnitude of KW increases to 10^{-3}, and the wear behavior becomes considerably more complicated and involves microfracture and compacted wear debris.Property TablePercentages in parentheses denote estimated combined relative standard uncertainties of the property values. For example, 3.0(5%) is equivalent to 3.0 +/- 0.15. Property values in parentheses are extrapolated values. Property [unit] 20 °C 500 °C 1000 °C 1200 °C 1400 °C 1500 °C ------------------------------------ ---------- ---------- ---------- ---------- ---------- ---------- Bulk Modulus [GPa].................. 203(3%) 197 191 188 186 184 Creep Rate [10^{-9}s^{-1}] at 300 MPa..... 0 0 0 0.004(17%) 0.27 1.6 Density [g/cm^{3}]..................... 3.16(1%) 3.14 3.11 3.10 3.09 3.08 Elastic Modulus [GPa]............... 415(3%) 404 392 387 383 380 Flexural Strength [MPa]............. 359(15%) 359 397 437 446 446 Fracture Toughness [MPa m^{1/2}]........ 3.1(10%) 3.1 3.1 3.1 3.1 3.1 Friction Coefficient [], 0.2 m/s,5 N 0.7(21%) 0.4 0.4 Hardness (Vickers, 1 kg) [GPa]...... 32(15%) 17 8.9 (6.9) (5.3) (4.6) Lattice Parameter a(polytype 6H) [Å] 3.0815(0.01%) 3.0874 3.0950 (3.0984) (3.1021) (3.1040) Lattice parameter c(polytype 6H) [Å] 15.117(0.02%) 15.144 15.179 (15.194) (15.210) (15.218) Poisson's Ratio [].................. 0.16(25%) 0.159 0.157 0.157 0.156 0.156 Shear Modulus [GPa]................. 179(3%) 174 169 167 166 165 Sound Velocity, longitudinal [km/s]. 11.82(2%) 11.69 11.57 11.52 11.47 11.44 Sound Velocity, shear [km/s]........ 7.52(2%) 7.45 7.38 7.35 7.32 7.31 Specific Heat [J/kg·K].............. 715(5%) 1086 1240 1282 1318 1336 Tensile Strength [MPa].............. 250(6%) 250 250 250 250 250 Thermal Conductivity [W/m·K]........ 114(8%) 55.1 35.7 31.3 27.8 26.3 Thermal Diffusivity [cm^{2}/s]......... 0.50(12%) 0.16 0.092 0.079 0.068 0.064 Thermal Expansion from 0 °C [10^{-6}K^{-1}] 1.1(10%) 4.4 5.0 5.2 5.4 5.5 Wear Coefficient(Log10)[],0.2 m/s,5 N -4.0(5%) -3.6 -3.6 ... ... ... Weibull Modulus [].................. 11(27%) 11 11 11 11 11