Microstructure and Electrochemical Properties of Refractory Nanocrystalline Tantalum-based Alloys

The nanocrystalline refractory tantalum alloys were made using mechanical alloying. The tantalum alloys were modified by niobium, molybdenum and tungsten in the concentration of 5, 10, 20 and 40 wt.%. The nanocrystalline powders were consolidated (hot-pressed) using the pulse plasma sintering mode. The hot pressing at the temperature of 1300 degrees C results in an increase of the grain size, in comparison to mechanically alloyed powders. However, the lowest grain size (significantly below 100 nm) was achieved for Ta-W alloys (approximately 40-60nm). The grain size was confirmed by XRD, TEM and AFM. The most uniform microstructure is also exhibited by the Ta-W alloys. The corrosion resistance was measured using the potentiodynamic mode in a chloride solution. The nanocrystalline Ta-Mo and Ta-W alloys achieved the same level of corrosion resistance as microcrystalline pure tantalum and 3 orders of magnitude better than pure nanocrystalline tantalum. Among all the prepared nanocrystalline tantalum alloys, the most promising properties exhibit those having 10% of the tungsten addition.