The effect of potassium doping on the strength of molybdenum

It has been demonstrated that the mechanical strength of the Group VIB refractory metals exhibits a strong size dependence. It is also recognized that the recrystallization behavior of refractory metals can be influenced strongly by the presence of small amounts of impurities. A well-known example is tungsten and its alloys. Considerable evidence has been presented demonstrating the important role of oxides and potassium bubbles in increasing the recrystallization temperature and preventing grain growth in tungsten at high temperatures. Despite some controversy about the exact species that is responsible for the above effect, this experimental result has been used commercially to produce long-life lamp filaments. Amongst refractory metals, molybdenum exhibits some special thermal properties, including a low coefficient of thermal expansion and high thermal conductivity. These properties make molybdenum an attractive choice for high temperature applications where dimensional stability is of concern. The addition of a slight amount (approximately 0.002 - 0.02 wt%) of CaO and MgO considerably increases the primary recrystallization temperature of molybdenum. These results illustrate the effect of oxide impurities on molybdenum. Therefore, it is conceivable that potassium doping of molybdenum can also produce a similar effect, specifically, inhibition of grain growth, as it does to tungsten. Inmore » this study, the authors demonstrate this effect, and furthermore, discuss the effect of the presence of potassium on the strength of molybdenum.« less