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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