**2. Oxide dispersion-strengthened W-based materials**

In ODS-W, nanoscaled oxides pin and hinder the migration of grain boundaries and dislocations in tungsten matrix, which improved the mechanical properties such as strength, recrystallization temperatures, and creep resistance. In addition, the dispersion of nanoscaled particles provides a large amount of phase interfaces that could act as sinks for irradiation-induced point defects and thus has the potential in improving the irradiation resistance [29, 31]. For instance, W-(0.3–1.0–2.0)wt%Y2O3 produced by mechanical alloying (MA) and hot isostatic pressing (HIPing) or microwave sintering has fine grains with the grain sizes ranging between 20 and 500 nm and containing a

### *The Tungsten-Based Plasma-Facing Materials DOI: http://dx.doi.org/10.5772/intechopen.88029*

high density (5.4–6.9 × 1022 m3 ) of nanosized Y2O3 particles with sizes between 1 and 50 nm [32, 33]. These refined grains and nanosized particles produce high densities of GB/PB interfaces, which generate high strength and a promising radiation resistance. To improve the ductility W-Y2O3 materials, different sintering and posttreatments such as spark plasma sintering (SPS) and high-temperature sintering in combination with hot rolling or hot forging deformation were used [34–38]. The performances of these W-Y2O3 were investigated as potential plasma-facing materials with respect to microstructures, thermal physical properties, mechanical properties, and thermal shock response when exposed to electron beam bombardment. For SPSed W-Y2O3, the tungsten grain exhibits an isotropic microstructure with an average grain size of 3.2 μm; the average of Y2O3 particles is about 80 nm [38]. For the sintered W-Y2O3 in flowing H2, Y2O3 particles are located at the grain boundaries with a typical bimodal size distribution, i.e., composing of two portions of particles with particle size of ~0.68 and 1.1–1.7 μm, respectively, and the average grain size of tungsten is about 3 μm [34]. The thermal conductivity of deformed W-Y2O3 showed nearly 35% and 17% higher values than that of SPSed W-Y2O3 at RT and at 1473 K, respectively [34]. The tensile tests showed that the deformed W-Y2O3 is ductile in the investigated temperature range of 673–1273 K with the total elongation between 4% and 10%. Three-point bending tests indicated that the deformed W-Y2O3 had a better mechanical strength and toughness. The determination of thermal shock response revealed a superior thermal shock resistance of the hot rolled W-Y2O3 [34]: no cracks but only surface roughening was found on the loaded surface after 100 shots at 0.6 GW/m2 for a pulse duration of 1 ms. Besides, the melting and recrystallization behaviors of deformed W-Y2O3 were less obvious than those of SPSed W-Y2O3 [34]. The discrepancy in thermal shock response between the two materials and in particular the superiority of deformed W-Y2O3 agrees well with the results that the better the thermophysical and mechanical properties, the better the thermal shock resistances. The high-energy-rate forging may significantly improve mechanical properties of W-Y2O3 materials [35]. It is indicated that needlelike grains ranging from a few to more than 50 μm in forged W-Y2O3 lead to the improved mechanical properties [35]. A detectable plastic deformation (TE = 2.9%) associated with work hardening occurs at 100°C, and the ultimate tensile strength of this forged W-Y2O3 material increases drastically to 1040 MPa.

For swaging deformed W-Y2O3, tungsten grains are round bar in shape [38]. The average diameter and length of tungsten grain in swaged W-Y2O3 are 4.6 and 26.7 μm, respectively, corresponding to an aspect ratio of about 6:1. The tensile results have shown that it is a brittle fracture until above 250°C and its strength is also smaller than that of the high-energy-rate forging ones [35], which implies that bimodal interfaces (in forged ones) are more in favor of strengthening and ductility. Therefore, it is important to notice that again the microstructure design, here from hot forging, is at least as important as the ODS effect. Although the addition of Y2O3 can produce PB interfaces and control GB interfaces, it cannot reduce the detrimental impurities of oxygen. Xie et al. [21] added Zr element into W-Y2O3 to absorb free oxygen at GBs to form Y-Zr-O particles, and at the same time, the particle size of Y-Zr-O can be further reduced. Because of the improved PB/GB interfaces by Zr, the strength and plasticity of this W-Zr-Y2O3 increase further on the base of W-Y2O3.
