High temperature hardness and slip system of NbB2 and TaB2 single crystals

TLDR: In this paper, the hardness of NbB2 and TaB2 single crystals was measured in the temperature range 20-1100°C on the (0001) plane in the 〈1010〉 and à 1120〉 indentation directions and on the {1010} plane in à 1210 à and [0001] directions.

Abstract: The high temperature Knoop hardness of NbB2 and TaB2 single crystals was measured in the temperature range 20–1100°C on the (0001) plane in the 〈1010〉 and 〈1120〉 indentation directions and on the {1010} plane in the 〈1210〉 and [0001] directions. In every case the hardness value H decreased monotonically with increasing temperature, but the H-T curves all showed a step at around 0.3T/Tm where Tm is the melting temperature, suggesting a change in the deformation mechanism at this temperature. At all temperatures the inequalities H 〈10 1 0〉(0001) > H 〈11 2 0〉(0001) and H 〈1 2 10〉{10 1 0} > H [0001]{10 1 0} were obtained for NbB2 and TaB2. This hardness anisotropy indicates that slip was mainly on the prismatic system and this was confirmed by slip line observations.