It is possible that they were intended to be used as tungsten filler metal. One of my former employers had some tantalum parts welded by a small specialist shop which also welded tungsten furnace fixtures. They claimed that tungsten is only a little harder to weld than tantalum. Of course tantalum is a royal bitch to weld even with its low melting temp of 5424 F compared to tungsten at 6164 F.