Effect of growth angle and solidification rate on the floating zone stability for processing of high-temperature pure metals

The height of floating zone and molten zone instability for five pure metals including Nb, W, Ta, Mo, and Ir with high melting points is investigated using electron beam floating zone method (EBFZM). The results show that the height level of floating zone for these five metals are in order with the sequence of Nb>Mo>W> Ta>Ir. The crystal growth angles for these metals are in the range of 8°~13° and the sample in large size can be developed by EBFZM as the growth angle is found not to be zero. Meanwhile, the actual growth angles are related with the interface growth mechanism. For continuous growth mechanism, the growth angles vary slightly with the solidification rate for rough interface, and for dislocation growth mechanism, the growth angles decrease with increasing the solidification rate. If faceting growth mechanism prevails, the growth angles drop remarkably at a low solidification rate and further increase with increasing the solidification rate. Additionally, by employing EBFZM growth of Ir and Mo pure metals, a solidification rate approaching 1 mm/min is available for controlling the growth angle and the height of floating zone. These calculations fit well with the experimental results of Mo single crystal prepared by EBFZM.