Abstract
Single-phase tungsten diboride (WB2) was synthesized at high pressure and high temperature. The different grain sizes ranging from 300 nm to 3 µm were successfully obtained in WB2 by controlling the experimental conditions. The effects of grain size on hardness and resistivity properties were investigated. The Vickers hardness of WB2 was modulated with grain size. The maximum asymptotic Vickers hardness is 25.5 GPa for WB2 with a grain size of 300 nm which is a 10% increase compared to WB2 with a grain size of 3 µm. The optimal electrical resistivity of WB2 was 10−7 Ωm with the biggest grain size of 3 µm, which is ascribed to low grain boundary density. The superior properties of hardness and electrical resistivity demonstrate that WB2 should be a new functional hard material replacing WC which is widely used in industrial production.
Highlights
Transition metal borides (TMBs) have been attracting considerable attention for their unique physicochemical properties, such as high melting point, hardness, electrical conductivity, wear resistance, thermal conductivity and chemical inertness, etc. [1,2,3,4]
We found that single phase WB2 without impurity is hard to synthesize
The phenomenon that stoichiometric phase pure WB2 cannot be synthesized by using a stoichiometric W/B atomic ratios precursor, often appears in transition metal borides (TMBs) synthesis, and may be caused by an inadequate proportion of B
Summary
Transition metal borides (TMBs) have been attracting considerable attention for their unique physicochemical properties, such as high melting point, hardness, electrical conductivity, wear resistance, thermal conductivity and chemical inertness, etc. [1,2,3,4]. Transition metal borides (TMBs) have been attracting considerable attention for their unique physicochemical properties, such as high melting point, hardness, electrical conductivity, wear resistance, thermal conductivity and chemical inertness, etc. In TMBs, tungsten diboride (WB2 ) was predicted to have a very high hardness ranging from 36 to 40 GPa and good conductive properties by first-principle calculation [3,9]. There is a paucity of reports about the hardness and conductive property of WB2. These reports about WB2 are ascribed to the fact that bulk WB2 is hard to synthesize at ambient temperature by traditional methods, such as self-propagating combustion synthesis [10], chemical vapor deposition (CVD) [11], and spark plasma sintering [7,12]. Even in high temperature sintering, WB2 will not exhibit any shrinkage [13]
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