High temperature resistance of novel tantalum-based nanocrystalline refractory compounds

In this work new tantalum-based nanocrystalline alloys and composites were made and tested under oxygen and nitrogen conditions using TGA. The materials were produced by mechanical alloying process. Niobium, molybdenum and tungsten were used as alloying elements, and TaC, ZrO2, and Y2O3 were used as the ceramic reinforced phase in composites, all in 5, 10, 20, and 40 wt ratio (wt.%). The materials were studied using XRD, SEM, TEM and AFM. For the purpose of thermal gravimetric analysis, the weight gain was measured and turned out to be the lowest for the Ta-W alloys. All nanocrystalline Ta alloys and composites exhibit lower weight gain in comparison to pure microcrystalline Ta. The Ta-5W alloy exhibits the highest activation energy. For other Ta alloys and composites the activation energy is lower in comparison to pure microcrystalline Ta. Annealing of bulk hot-pressed Ta compounds in oxidative and nitrogen atmosphere leads to the formation of an external thick oxide coating which is loosely connected to the surface and of the diffusion nitride layer inside the material surface, respectively. In this work the authors demonstrate that nanocrystalline Ta-based alloys and composites have a better thermal stability against oxidation in comparison to microcrystalline tantalum. (C) 2019 Elsevier B.V. All rights reserved.