The physical, chemical, and mechanical properties of tungsten are at the far limits of all engineering materials. These unique properties, particularly ultra-high strength, density, and melting point, create enticing prospects for using tungsten in extreme engineering environments for nuclear, military and space applications. However, these environments also require materials that resist fracture, which presents a significant challenge for tungsten, particularly at low temperatures. This review discusses several significant factors that affect the ductile to brittle transition and low temperature ductility of tungsten. The effects of crystal structure, dislocation structure, and microstructure to describe competing factors in the plasticity and fracture of tungsten at low temperatures are assessed. In particular, the dislocation structure and the mechanisms of dislocation mobility are shown to be critical to understanding plasticity at low temperatures.

Mechanisms of deformation and ductility in tungsten – A review

We aimed to clarify the behavior of change in the grain structure and hardness of hot-rolled pure W and its alloys plates developed for various properties by holding at high temperature for long and short durations in the absence of irradiation. The isothermal annealing was performed at 1100 °C for 10–3115 h. The isochronous annealing was performed for 1 h in a temperature range of 1100 to 2300 °C. After heat treatment, the grain structure was observed using electron backscatter diffraction (EBSD) and the Vickers hardness was measured in the observed plane. Pure W did not recrystallize by the heat treatment for a short duration of 1 h at 1100 °C, while the recrystallization of pure W progressed during the heat treatment for long duration of 3115 h at 1100 °C. The temperature and duration at which the recrystallization occurs increase because of the dispersion of K bubbles and solid solution of Re. Considering the actual operation period of fusion reactors, a temperature of 1100 °C can result in recrystallization. It is necessary to decrease the maximum operating temperature or to use materials having a high recrystallization temperature by alloying.

Recrystallization behavior of hot-rolled pure tungsten and its alloy plates during high-temperature annealing

Mechanical properties of tungsten: Recent research on modified tungsten materials in Japan

https://pureadmin.qub.ac.uk/ws/files/92125627/DGT_W_final_version_with_modification.pdf

High-resolution measurement and mapping of tungstate in waters, soils and sediments using the low-disturbance DGT sampling technique

The effects of cold and warm rotary swaging and subsequent post-process annealing on mechanical properties, residual stress, and structure development within WNiCo powder-based pseudo-alloy were predicted numerically and investigated experimentally. The swaging temperature of 900 °C imparted increase in the Young’s and shear moduli; the post-process annealing at 900 °C also imparted decrease in the residual stress values, primarily due to structure recovery introduced within the matrix. Cold rotary swaging at 20 °C imparted ultimate tensile strength of almost 1 900 MPa, while warm rotary swaging at 900 °C introduced increased plasticity (almost 24 % after a single swaging pass). Post-process heat treatment promoted diffusion of W to the Ni/Co matrix, which increased strength, but remarkably decreased elongation to failure and residual stress. Numerically predicted results of mechanical behaviour corresponded to the experimental results and confirmed the favourable effects of the selected thermomechanical treatments on WNiCo performance.

Effect of thermomechanical processing via rotary swaging on properties and residual stress within tungsten heavy alloy

From a historical point of view, the development of the PM processing steps and tools “for making tungsten ductile” by William D. Coolidge in 1909 marks the breakthrough for the usage of tungsten filaments in the lighting industry and the beginning of the industrial era of modern Powder Metallurgy. Some important technological developments before introducing the Coolidge process will be described briefly (Just and Hanaman procedures, Kuzel process, Pintsch method) together with the corresponding implications for today's modern technologies and materials (Sol-Gel, CVD, MIM, ODS alloys, W-RE welding electrodes). With regard to the Coolidge process some always recurring misunderstandings, especially of the doping process, will be corrected. In addition, some accompanying discoveries and inventions (Tungsten Heavy Metals, Gradient Materials, Cemented Carbides) will be mentioned too. Finally, the scientific importance of the potassium bubbles as the strongest pinning points at highest temperatures against the movement of dislocations and grain boundaries will be highlighted shortly. Considering geometrical dimensions, the microstructural features of the finest wires and the corresponding fabrication of diamond dies, necessary for the deformation of wires, also represent precursors of today's nanotechnology and micromachining.

P. Schade

Papers

100 years of doped tungsten wire