Thermal-induced microstructural coarsening of heavy drawn pure tungsten wire

This study systematically investigates the recrystallization behavior and microstructural evolution of ultrafine drawn tungsten wire (25 μm) under various heat treatment conditions. Utilizing electron backscatter diffraction (EBSD) and microhardness tests, the research reveals that the as-drawn tungsten wire exhibits a fibrous structure parallel to the drawing direction, with an average grain size of 78 nm. This structure features a high proportion of high-angle grain boundaries (86.5%), predominantly Σ3 boundaries. Key findings from the study indicate that when the annealing temperature remains below 1100 °C, the tungsten wire demonstrates a degree of thermal stability with a hardness higher than 530 HV 0.1 . Its microstructure evolution during this stage is primarily driven by the release of stored energy through dislocation activity. However, when the temperature exceeds 1100 °C, the fibrous grain rapidly transitions into an equiaxed recrystallized structure. This transformation is accompanied by a notable increase in the proportion of Σ3 grain boundaries and a sharp decline in hardness. Kinetic analysis further delineates the recrystallization process into two distinct stages: the low-temperature stage, which is dominated by dislocation annihilation, and the medium-to high-temperature stages, where grain coarsening is achieved through grain boundary migration and grain rotation. This research provides a critical experimental basis for understanding the mechanism behind the thermal stability performance of heavy drawn tungsten wires and offers significant guidance for expanding the high-temperature applications of tungsten.