Fang Qianfeng, a researcher of the Institute of Solid State Physics, Chinese Academy of Sciences, has made important progress in the development of nanostructured tungsten-based alloys, and successfully prepared high-strength dual-nanostructure tungsten materials through pressure-assisted low-temperature densification sintering. Related work was published in the International Journal of Refractory Metals and Hard Materials (Int. J. Refract. Met. H. 80, 104-113 (2019)).
Link: https://www.sciencedirect.com/science/article/pii/S0263436818306528
Tungsten-based alloys are considered to be the most promising plasma-oriented first wall materials that can be used in extreme environments of fusion reactors, but the brittleness of commercial pure tungsten greatly limits its application. Oxide dispersion strengthening (ODS) is one of the effective ways to improve the toughness of tungsten-based alloys. However, the current ODS-W has a large oxide particle size and cannot achieve the desired toughening effect. In response to this problem, the researchers used the solution-precipitation mechanism in ODS-Fe to control the size of oxide particles below 3 nm, and successfully prepared a double nanostructured tungsten material by means of pressure-assisted low-temperature densification sintering: W Grain size ~ 67 nm and Y2Ti2O7 oxide particle size ~ 10 nm.
The researchers first "solid solution" Y2O3 and Ti into the W matrix through high energy ball milling, and then used spark plasma sintering (SPS) technology to densify and sinter the W-1.0% Y2O3-0.7% Ti powder after high energy ball milling. Strictly controlling the sintering temperature makes the nano-scale Y2Ti2O7 particles precipitate and evenly distributed in the tungsten matrix. These fine second-phase nanoparticles inhibit the growth of tungsten grains, and finally achieve a double nanostructure W-1.0% Y2O3-0.7% Ti Preparation of bulk alloy materials. XRD and TEM results show that the average size of W grains is 67 nm, and the average particle size of oxide particles in the grains and grain boundaries are 8.5 nm and 16.4 nm, as shown in the figure. The micro-Vickers hardness of this nanostructured W alloy is as high as 1441 Hv, which is 2-3 times that of the ordinary W alloy reported in the literature. The extremely high micro hardness comes from the synergistic strengthening effect of nano-scale W grains and uniformly dispersed nano-oxide particles. This solid solution-precipitation process provides a common way to prepare nanocrystalline refractory metals by dispersing nanoscale oxides in a controlled manner.