Effect of heating rate on the recrystallization behaviour of doped tungsten

Abstract

The influence of heating rate on the development of primary and secondary recrystallized grain structure of heavily drawn KSiAl-doped tungsten wires has been studied by using TEM, SEM, EEM and microhardness measurements. The observed difference in the microstructures between the rapidly and slowly heated wires is discussed in terms of the interaction between grain boundaries and bubbles. It is suggested that on slow heating, the boundaries of the widening fibers can move slowly enough to drag along partial or entire bubble rows. As a result of the collective motion of bubbles and boundaries, longer "secondary" bubble barriers can form from the shorter original "primary" ones, thereby contributing to the evolution of the recrystallized grains with high aspect ratio. From microhardness measurements and from the results of EEM experiments, it is also concluded that slow heating decreases the driving force for secondary recrystallization requiring a higher temperature at which the enhanced grain boundary mobility results in a large grained structure of the wire.