Tantalum or tantalum-based alloys are preferably prepared by vacuum melting. Vacuum arc remelting (VAR), electron beam melting (EBM), or plasma arc melting (PAM) are also vacuum melting methods that can be used to form alloys. To prepare the actual alloy, at least one element selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, molybdenum, tungsten and rhenium (Ru, Rh, Pd, Os, Ir, Pt, Mo, W and Re) is added to pure tantalum material or essentially pure tantalum material or tantalum alloy using one of the vacuum melting methods listed above. Tantalum alloys preferably contain tungsten as well as platinum, molybdenum, rhenium or mixtures thereof. Although it is indicated above that VAR, EBM, or PAM can be used, the preferred technology is VAR.
Examples of tantalum alloys with a tantalum content of at least 89% include, but are not limited to, Ta-3W(tantalum-tungsten) containing at least about 3% tungsten, Ta-3W-Pt (tantalum-tungsten and platinum alloy) containing at least about 3% tungsten, Ta-3W-Mo (tantalum-tungsten and molybdenum alloy) containing at least about 3% tungsten, and Ta-3W-Re containing at least about 3% tungsten Tantalum-tungsten and rhenium alloy. Ta-3W-Pt, Ta-3W-Mo, and Ta-3W-Re can be formulated and manufactured in a manner similar to the preparation of Ta-3W. Alloys are preferably prepared by microalloying other metals with Ta-3W(tantalum-tungsten) alloys.
Another preferred embodiment is the addition of ruthenium, rhodium, palladium, osmium, and iridium (also known as "platinum group metals", i.e., PGMS), which also provide low hydrogen overvoltage sites to stabilize the Ta2O5 oxide layer.
The advantages of the new alloy over pure Ta-3W are its excellent corrosion resistance and hydrogen brittleness resistance. Adding platinum is the most preferred embodiment because platinum has the most free electrons and theoretically attracts additional oxygen atoms, helping to seal holes in the Ta2O5 oxide layer and/or providing sites with low hydrogen overvoltage, thereby stabilizing the Ta2O5 oxide layer.
The samples were prepared using laser addition manufacturing (LAM) or traditional vacuum arc remelting (VAR) techniques. In the former technique, powders mixed with tantalum, tungsten and platinum are formed as desired, then melted and consolidated under inert conditions using a laser. In these samples, the final tantalum alloy contains 2.8 % tungsten by weight and 500ppm platinum. In the latter technique, the powder mixed with tantalum and platinum is pressed into a powder leech as required and welded to the side of the NRC76 rod (this assembly is herein referred to as the "electrode"). The electrode is then melted using a traditional vacuum arc remelting (VAR) technique. In these samples, the final tantalum alloy contains 2.8 % tungsten by weight and 10,000 PPM platinum.
