NIST Standard Reference Database 150
Last Update to Data Content: 2002
Journal Reference: "Material Properties of Titanium Diboride," R. G. Munro, Journal of Research of the National Institute of Standards and Technology, Vol. 105, pp. 709-720 (2000).
Other materials: Property Data Summaries
Nearly fully dense polycrystalline TiB2 can be produced by a variety of processing methods, including sintering, hot pressing, hot isostatic pressing, microwave sintering, and dynamic compaction. The relatively strong covalent bonding of the constituents, however, results in low selfdiffusion rates. Consequently, given also a high melting point of (3225 ± 20) °C, pressureless sintering of TiB2 requires a relatively high sintering temperature, on the order of 2000 °C. Unfortunately, grain growth is also accelerated by the higher temperature, and the anisotropy of the hexagonal grain structure results in deleterious internal stresses and the onset of spontaneous microcracking during cooling. Grain growth can be limited and densification enhanced by the use of sintering aids such as Cr, CrB2, C, Ni, NiB, and Fe. The solubility of TiB2 in liquid Ni and Fe appears to be especially useful in this regard. In such cases, the mass fraction of the sintering aid in the specimen may range from 1 % to 10 %, while the sintering temperature may be reduced to the range of 1700 °C to 1800 °C for sintering times on the order of 1 h. Successful hot pressing with Ni additives can be achieved with a hot pressing temperature as low as 1425 °C with a sintering time of 2 h to 8 h.
The data presented here were derived from reported values for a narrowly defined material specification. Using trend analysis, property relations, and interpolation methods, the selfconsistent trend values for the properties of polycrystalline TiB2 were determined for a mass fraction of TiB2 of at least 98 %, a density of (4.5±0.1) g/cm3, and a mean grain size of (9±1) µm.
For references to the source data and detailed discussions of the properties, please refer to the Journal Reference.
TiB2 crystallizes with hexagonal symmetry, space group P6/mmm, and has one formula unit per unit cell. The lattice parameters (a,c) have a slight quadratic dependence on the temperature which accounts for the linear temperature dependence of the coefficient of thermal expansion. The ratio c/a ranges from 1.066 ± 0.001 at 25 °C to 1.070 ± 0.001 at 1500 °C. Individually, the lattice parameters may be expressed as:a/Å = 3.0236 + 1.73x10-5 (T/K) + 3.76x10-9 (T/K)2
where T is in the range from 293 K to 2000 K. The relative standard uncertainties, ur, when using these expressions are estimated to be ur(a) = 0.03 % and ur(c) = 0.04 %.Creep Characteristics (flexure at 100 MPa and T > 1500 °C):
The wear behavior of TiB2 appears to be complicated by its interaction with oxygen in the atmosphere. Results from a ring on block test of the wear of TiB2 for a density of 4.32 g/cm3 and a grain size of 2 µm showed that for temperature less than 600 °C, the amount of material removed during the test increased with increasing sliding distance, but decreased with increasing temperature. For temperature greater than 600 °C, the specimens gained mass with the amount of mass gain increasing with increasing sliding distance. The decrease of mass loss and the occurence of mass gain appear to be the result of the formation of B2O3 in the wear track of the specimens. The coefficient of friction appears to have a power law dependence on the ratio of the sliding speed vslide and the contact stress Pload. For vslide/Pload = 0.2 m s-1 MPa-1, the coefficient of friction may be taken to be 0.8 ± 0.1 for temperature less than or equal to 400 °C and 0.4 ± 0.1 for temperature in the range 800 °C to 1000 °C.
The values presented here are trend values derived for polycrystalline TiB2 specimens with a purity (mass fraction of TiB2) of at least 98 %, a density of (4.5±0.1) g/cm3, and a mean grain size of (9±1) µm. Estimated combined relative standard uncertainties of the property values are listed in the last column. For example, a value of 3.0 with ur = 5 % is equivalent to 3.0 +/- 0.15. A question mark, (?), for ur means the uncertainty could not be determined with the available data.
|Property [unit]||20 °C||500 °C||1000 °C||1200 °C||1500 °C||2000 °C||ur [%]a|
|Bulk Modulus [GPa]||240||234||228||24|
|Compressive Strength [GPa]||1.8||?|
|Creep Rateb [10-9 s-1]||0.005||3.1||20|
|Elastic Modulus [GPa]||565||550||534||5|
|Flexural Strength [MPa]||400||429||459||471||489||25|
|Fracture Toughness [MPa m1/2]||6.2||15|
|Friction Coefficientd ||0.9||0.9||0.6||15|
|Lattice Parameterf a [Å]||3.029||3.039||3.052||3.057||3.066||3.082||0.03|
|Lattice Parameterf c [Å]||3.229||3.244||3.262||3.269||3.281||3.303||0.04|
|Poisson's Ratio ||0.108||0.108||0.108||70|
|Shear Modulus [GPa]||255||248||241||5|
|Sound Velocity, longitudinal [km/s]||11.4||11.3||11.2||5|
|Sound Velocity, shear [km/s]||7.53||7.47||7.40||3|
|Specific Heat [J/kg·K]||617||1073||1186||1228||1291||1396||1.5|
|Thermal Conductivity [W/m·K]||96||81||78.1||77.8||6|
|Thermal Diffusivity [cm2/s]||0.30||0.17||0.149||0.147||6|
|Thermal Expansiong, a axis [10-6K-1]||6.4||7.0||7.7||7.9||8.3||8.9||7|
|Thermal Expansiong, c axis [10-6K-1]||9.2||9.8||10.4||10.6||11.0||11.6||5|
|Thermal Expansionh, average [10-6K-1]||7.4||7.9||8.6||8.8||9.2||9.8||6|
|Weibull Modulus ||11i||?|