Structure and properties of tantalum carbide crystals

Abstract

Single crystals of tantalum carbide, up to 2 mm in size have been grown from solution in a bath of molten iron. The slip plane was found to be {111} using a two-surface analysis on etch-pitted crystals deformed by microindentation at room temperature. Observations of etch-pit patterns around inclusions suggest that slip occurs on other planes at elevated temperatures. Maximum microhardness values between 3800 and 5200 Knoop (100 gm load) were found at a composition TaC_0.83±0.01. In regions of crystals with a carbon content less than TaC_0.83 a phase transformation was seen close to microhardness indentations in samples decarburised below 2200† C. The mechanical behaviour of tantalum carbide is discussed with reference to a general model for the electronic structure of carbides.