The hardness of NbB2 single crystals

NbB2 single crystals grown from an aluminium solution were characterized by an electron microprobe analysis, chemical etching and X-ray topography, and the hardnesses of the crystals were measured at room temperature. Single crystals have nearly stoichiometric compositions with slight impurities and high crystal perfections. The hardness measurements were made on the (0001) and (101̄0) planes with a Knoop indenter in various directions. The hardness was a maximum when the long axis of the indentation was in the 〈1̄010〉 direction and a minimum when the long axis was in the 〈12̄10〉 direction on the (0001) plane. The values of the hardness did not vary much in the (101̄0) plane. It was shown that in the single crystals two types of prismatic slip occurred at room temperature. © 1979.