Microstructure evolution and mechanical properties of an ultra-high purity tungsten

Tungsten has been usually applied in some extreme high-temperature environments owing to its high melting point, high-temperature stability and excellent thermal conductivity. In this study, a kind of ultra-high purity tungsten (UHP-W) is developed by multi-step rolling and recrystallization annealing of chemical vapor deposition tungsten. The purity is better than 99.9999 wt% with all trace elements below detection limits. The ductility of UHP-W can be improved through annealing, and a total tensile elongation of up to 30 % is achieved when tested at 300 °C. Electron backscatter diffraction analysis reveals that UHP-W develops an inhomogeneous microstructure consisting of deformed elongated grains and recrystallized blocky grains. Ultra-high purity purifies grain boundaries, which is beneficial for enhancing intergranular cohesion. Multiple slip systems are activated during tensile deformation. A mixed-mode crack propagation is observed, which increases the total work of fracture.