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Lower structural perfection of W-Ta single crystals is associated with considerable disturbance of the melt by plasma arc, great temperature gradients and cooling rate of the growing single crystal due to “air rinsing” of its surface by plasma-forming gas. In the peripheral areas of this sample a large number of small sub-grains is presented, which confirms the trend towards fragmentation of the structure at crystallization from the beginning to the end of the ingot.