Effects of cooling rate on the microstructure and hardness of TiC-VC alloys

Abstract

A study has been made of the effect of cooling rate from 1350$sup 0$C on the microstructure and microhardness of well characterized TiC--26 wt percent TiC- -26 wt percent VC and VC--22 wt percent TiC, with carbon to metal ratio close to 0.84. For the VC--22 wt percent TiC alloy it has been found that as the cooling rate is decreased the room temperature microhardness is also decreased, vacancy domain contrast becomes optically resolvable and a second phase is precipitated. At room temperature domain size hardening is thought the most likely origin of the strengthening. A reduction in cooling rate of TiC--26 wt percent VC alloys results in a significant increase in the room temperature microhardness but no visible change in the optical microstructure, when viewed by either normal or plane polarized white light. The electron microscope observations, of the VC--22 wt percent TiC alloy, previously reported and the present results suggest that above 1350$sup 0$C the mechanical properties cannot be related to a two-phase microstructure, as had tentatively been suggested in an earlier study. (auth)