**3.1. Types of W-based composites**

increases with an increase in the radiation level [29]. Low-temperature brittleness imposes

The development of a melt layer due to an intense thermal transient condition stimulates the generation of highly activated dust particles. Due to the interaction with high-energy ions, W can undergo additional erosion [1]. W shares a common disadvantage with other high-Z materials, i.e., very low acceptable impurity concentrations in the plasma, thus requiring almost perfectly controlled plasma [1]. The recombination rate coefficient for H2 is very high in W, and the high hydrogen content results in bubbles and blisters. Keeping W at an elevated temperature will increase the blisters and the inventory problem [9]. He bubbles are also

Due to its high hardness, high brittleness, and poor machinability, the manufacturing of W parts is very costly and time-consuming [20]. The joining of W to a Cu-based (CuCrZr) heat sink is troublesome, owing to the large difference in the CTEs of these two materials [18]. Considering all of these shortcomings, it can be said that further enhancements of the prop‐

Pure W shows favorable behavior for applications to high-temperature and plasma-facing applications. Regarding the aforementioned limitations, research is in progress to improve W and make it useful in future fusion reactors [4]. Currently, research in the field of plasma-facing materials focuses on determination of the impacts of ion irradiation on the properties of W [4]; improvements of its mechanical properties [1], such as its ductility [19] and fracture toughness [15]; methods to mitigate its brittleness [26]; and clarifications of the activation of this material

Various options are being utilized for modifications and improvements of these properties. Some of these techniques involve (i) W-based composites [19], (ii) nanocrystalline W-based materials [1, 5, 34], (iii) W–X (X=Ta, Re, Mo, V, Ti, etc.) alloys created by powder metallurgy [15, 35–39], (iv) the dispersion of ductile fibers in W by mechanical synthesis [25], (v) the dispersion of ceramic particles of transition metals [13], (vi) the addition of rare-earth oxide particles into W [26], (vii) effective energy dissipation caused by controlled cracking and friction at fiber/matrix interfaces [28], and the utilization of functionally graded materials (FGMs) as an efficient solution to the joining problem of W to copper-based heat sinks [34], (viii) the creation of laminated hybrid composites [18], (ix) the post-processing of W to obtain full densification [21], and (x) the addition of a sintering activator to obtain high density levels

All of the abovementioned methods and techniques have some influence on the properties of W. For instance, equal-channel angular pressing (ECAP) reduces the brittleness and improves the toughness and strength of ultrafine (0.9 μm) equiaxed grains of W [21], as ECAP ultra-finegrained W exhibits much smaller cracks as compared to coarse-grained W around dents produced by microhardness tests even at 250°C [30]. Plasma spraying offers high adhesion

restrictions on the application of tungsten as a structural material [25, 27, 28].

observed when W samples are exposed to He plasma [31–33].

erties of W are essential prior to its commercial use [4, 18].

**2.2. Recent trends to enhance the performance of W**

[2].

142 Nuclear Material Performance

[21].

The research focusing on incorporating W with enhanced high-temperature properties and irradiation resistance via composite materials is multidimensional. Various types of W-based composites, including dispersion-strengthened, particle-reinforced, fiber-reinforced, and laminated composites, as illustrated in **Figure 2**, are being developed and investigated.

**Figure 2.** (a) ODS and/or ceramic particles reinforced composites, (b) whisker reinforced composites, (c) fiber rein‐ forced composites and (d) laminated/3D composites.
