Open billet
Tantalum cannot be processed using ordinary methods for processing general metals. The initial process is generally forging, processing, and heat treatment,
Produce flat billets or circular small and medium-sized billets through two methods: hammering and stamping. Unlike other metals, tantalum cannot be thermally processed. The recrystallization temperature of tantalum exceeds 1000~C. If heated, even with a general protective layer, excessive oxidation will occur. What's more serious is that if tantalum is exposed to such high temperatures, not only does it undergo excessive oxidation on its surface, but oxygen can also invade between the atoms inside the matrix, making tantalum brittle. Not only oxygen, but also nitrogen, carbon, and hydrogen can make tantalum brittle. Due to the above reasons, tantalum is generally not subjected to thermal processing. When thermal processing is necessary, a protective coating should be applied or carried out in an inert gas atmosphere.
heat treatment
Due to the active reaction between tantalum and oxygen, it is necessary to avoid heat treatment in an atmosphere with even a small amount of air. Therefore, almost all annealing is carried out in high vacuum, and the airtightness of the heating furnace must also be high. Usually, the heat treatment temperature of tantalum is between 950~1300 ℃. Tantalum and commonly used tantalum alloys do not undergo phase transformation within this temperature range. Heat treatment is only used for annealing, so the heating temperature and cooling rate are not important. It is better to have a slightly longer heat treatment time to achieve complete recrystallization.
Tantalum produced commercially has high purity. The grains become very large through annealing. The size of crystal grains is determined by cold processing, purity, temperature, and process steps. Therefore, temperature control and process control are important means to determine the size of crystals.
Tantalum, unlike many other metals, must be very clean before heat treatment. If not cleaned thoroughly, surface contamination caused by hydrogen, oxygen, nitrogen, and carbon will occur, resulting in brittle (hardened) tissue. Because hydrogen, oxygen, nitrogen, and carbon are highly active invasive elements within the temperature range of tantalum annealing, once contaminated by these elements, there is no other way to remove them except by remelting.