NIST Property Data Summaries for Advanced Materials

NIST Standard Reference Database 150


Sintered Silicon Carbide ( SiC )

Reference: NIST Structural Ceramics Database, SRD Database Number 30

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

Material Summary:

Sintered silicon carbide ceramics typically are produced using submicrometer powders that have been extracted from an Acheson furnace and ground to a fine particle size. Boron and carbon are used as sintering aids to achieve improved densification during sintering which is typically conducted at a temperature on the order of 2500 °C. The resulting microstructure consists predominantly of fine, equiaxed grains of the hexagonal SiC polytype 6H. A small amount of free carbon and isolated B4C grains may be present also as remnant artifacts of the sintering aids.

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.

Property Summary:

    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 Table
    Percentages 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/cm3].....................  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 m1/2]........  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 [cm2/s].........  0.50(12%)     0.16         0.092        0.079        0.068        0.064
    Thermal Expansion from 0 °C [10-6K-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