Variations in Tantalum Carbide Microstructures with Changing Carbon Content



A wide variety of microstructures have been obtained by vacuum plasma spraying (VPS) 39Ta:61C atomic percent feedstock powders. During processing, the powder feed was fed through a high energy VPS plasma plume, where altering nozzle angle changed the overall retained carbon concentration in the deposited material. The samples were subsequently sintered and hot isostatic pressed to homogenize and consolidate the microstructure. The microstructures consisted of grains that were either equiaxed or acicular. In the samples with less carbon loss, the equiaxed grains were either the TaC phase or a TaC matrix that encased fine laths of Ta4C3. In the sample with the most carbon loss, acicular grains were found containing layered and parallel TaC, Ta2C, and Ta4C3 laths along the major-axis of the grains. The phases of the compounds have been determined by using complimentary X-ray diffraction and electron diffraction techniques. Focused ion beam serial sectioning and transmission electron microscopy tilt series tomography were performed to generate three-dimensional reconstructions of the microstructure morphologies. This article addresses how tantalum carbide microstructures are controlled by the overall concentration and phase fraction content in each of these samples.