Effect of dopants on the secondary grain growth in tungsten sheet

In order to understand in detail the secondary recrystallization behaviour of rolled tungsten sheet doped with CaO and/or MgO, the effect of dopants on the secondary grain growth behaviour was investigated using EPMA and chemical analyses. It was found that the doping elements CaO and/or MgO play an important role in the grain growth of the hot-rolled tungsten, initially restraining growth in the fine-grained primary recrystallized matrix and subsequently promoting the abnormal grain growth of a secondary grain at higher temperatures. Consequently a large-scale single crystal sheet can easily be obtained from a hot-rolled tungsten sheet doped with CaO and/or MgO. Moreover, the temperature at which secondary recrystallization commences from hot-rolled sheet is strongly dependent on the kinds of dopant and is correspondent to their dissociation temperatures. Chemical and EPMA analyses indicate that the particles consisting of CaO and/or MgO are present much more frequently at the primary grain boundaries than the matrices and survive at high temperatures just below the secondary recrystallization temperature. These results may be closely related to the dissociation and dissolution mechanism of the dopants on the secondary grain growth in the hot-rolled tungsten sheet. 6 refs., 9 figs., 1 tab. (Author)