* Astronomy

Title: Tungsten tetraboride, an inexpensive superhard material
Authors: Reza Mohammadi, Andrew T. Lech, Miao Xie, Beth E. Weaver, Michael T. Yeung, Sarah H. Tolbert, and Richard B. Kaner

Tungsten tetraboride (WB4) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB4 was successfully synthesized by arc melting from the elements. Characterisation using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesised material is phase pure. The zero-pressure bulk modulus, as measured by high-pressure X-ray diffraction for WB4, is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 ± 2.9 GPa under an applied load of 0.49 N. Various ratios of rhenium were added to WB4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to approximately 50 GPa at 0.49 N. Powders of tungsten tetraboride with and without 1 at.% Re addition are thermally stable up to approximately 400 °C in air as measured by thermal gravimetric analysis.

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