The development of high performance nanocrystalline tungsten based alloys
Recently, the research group of the Institute of Solid State Physics, CAS has made new progress in the development of nano-structured tungsten based alloy, and successfully prepared high strength double-nanostructured tungsten materials by pressure-assisted low-temperature densification and sintering. The work was published in the International Journal of Reacting Metals and Hard Materials.
Tungsten-based alloys are considered to be the most promising plasma-oriented first-wall materials that can be used in the extreme environment of fusion reactors, but the brittleness of commercial pure tungsten greatly limits their application. Oxide dispersion strengthening (ODS) is one of the effective ways to improve the toughness of tungsten alloy. However, the oxide particle size in ODS-W is too large to achieve the ideal toughening effect. In order to solve this problem, the researchers learned from the experience of controlling oxide particle size below 3nm in ODS-Fe by solid solution-precipitation mechanism, and successfully prepared tungsten materials with double nanostructure by pressure-assisted low-temperature densification and sintering: W grain size ~67 nm and Y2Ti2O7 oxide particle size ~ 10 nm.
Firstly, the "solid solution" of Y2O3 and Ti into the W matrix was carried out by high-energy ball milling. Then, the densification and sintering of W-1.0%Y2O3-0.7%Ti powder after high-energy ball milling was carried out by discharge plasma sintering (SPS) technology. The nanoscale Y2Ti2O7 particles were precipitated by strictly controlling the sintering temperature. These fine second-phase nanoparticles inhibit the growth of tungsten grains, and finally realize the preparation of double-nanostructure W-1.0%Y2O3-0.7%Ti bulk alloy materials. XRD and TEM results show that the average size of W grain is 67nm, and the average size of oxide particles in the grain boundary and inner-grain are 8.5nm and 16.4nm, respectively. The micro-Vickers hardness of this nanostructured W alloy is up to 1441 HV, which is 2-3 times that of ordinary W alloys reported in the literature. The extremely high microhardness is due to the synergistic strengthening effect of nanoscale W grains and uniformly dispersed nano oxide particles. This solution-precipitation process provides a general approach for the preparation of nanocrystalline refractory metals by dispersing nanoscale oxides in a controlled manner.
