**5. Summary and outlook**

The improvements in different aspects of tungsten have been enriching the knowledge base and help to show the way to high-performance tungsten materials for fusion applications. Nevertheless, to satisfy the requirements of PFCs in future fusion facilities, the performances of tungsten materials need to be further improved, which may be achieved through several approaches as follows. Firstly, microstructure optimization includes the size and shape of tungsten grains and the size, distribution, and the number density of second-phase particles in tungsten-based materials. For ODS-W or CDS-W, the size of strengthening particles is not small enough; if secondphase particles could be further refined, e.g., to 10 nm or even smaller, more favorable particle-matrix interfaces would be constructed, and thus mechanical properties, resistance to thermal loads, and irradiation might be further improved. Secondly, to reduce the DBTT and improve the low-temperature ductility, the content of detrimental interstitial impurities (i.e., O, N) should be as low as possible. For the Wf/W composites, the interface is still a weak point and needs to be further optimized.

For the materials used in fusion reactors, the synergistic effects of multi-loadings including high thermal loads, high-flux H/He plasma etching, and neutron irradiation may lead to much more severe degradation of properties. Therefore, the synergistic effects of high heat loads, low-energy high-flux plasma etching and neutron irradiation, and transmutation elements on the microstructures and properties of tungsten materials need to be systematically investigated in the near future, which is necessary to evaluate the performance of the tungsten materials more accurately, and the corresponding database for the performance of tungsten materials should be established.
