The present status of metallic materials research for nuclear fusion reactors from the point of view of radiation damage is reviewed. First of all, the Japanese program of fusion reactor construction is described. Then the general description of radiation damage of the first wall of fusion reactors is given. This is followed by the detailed discussions of important problems such as He/dpa ratio, swelling and its atomistic mechanism, neutron spectrum tailored irradiation, and so on. Finally, the Japanese program of alloy development for the first wall of nuclear fusion reactors is discussed.

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The mathematical expression of the trajectory of injected gas stream at lower velocities in liquid was derived by approximating it as the trajectory of a single rising gas bubble. The experimental time-average images of air stream in water were compared with this trajectory and the trajectory of gas jet of higher velocities derived by Themelis et al., respectively. The experimental results coincided with the Themelis’ equation when the Reynolds number at the orifice is higher than 9000. They agreed with the trajectory of a single gas bubble at the Reynolds number lower than 6000.

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The stress and temperature dependence of steady state creep rates, recovery rates (r=−∂σ⁄∂t) and work hardening rates (h=∂σ⁄∂ε) were studied. The rate controlling mechanism changed from bulk to core-diffusion at about 673 K. Application of the Yoshinaga’s discriminant revealed that the effective stress level of flow stress is negligibly small.
Measurements of r and h were conducted by stress relaxation tests. The results were compared with a network growth theory of creep. Coincidence between the experiments and the theory was fairly good.

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The development of shear bands has been investigated metallographically on (211)[\bar111] copper single crystals rolled at room and liquid nitrogen temperature (RT and LNT), respectively. The shear bands at the LNT rolling appear in the lamellae of mechanical twins, while those at the RT rolling occur in the slip deformed crystal. Although these two types of shear bands show great differences from each other in nucleation sites, development behavior and microstructures, these differences will be attributed to whether mechanical twinning occurs or not in the crystals during rolling. It will be inferred that the shear bands can be formed in the (211)[\bar111] crystal accompanied by localized deformation, which may be brought about by straining the mechanical twin lamellae at LNT and by unequal activation of multiple slip systems at RT.

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Behaviours of the grain boundary sliding (GBS) in high temperature creep of a precipitate-free 25Cr–20Ni austenitic stainless steel were investigated over a range of stress (29.4–44.1 MPa), temperature (1153–1193 K) and grain size (30–540 μm). Results on the GBS measured on the specimen-surface exhibit that the strain resulting from the GBS is less than 14% of the overall strain, the effects of stress, temperature and grain size on the GBS being individually identified. It is, therefore, concluded that the overall strain rate (the steady state creep rate) is controlled by the deformation within grains. It is also found that the formation of intergranular cracks and voids is caused by the GBS. The GBS is thus an important factor for the creep rupture.

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The yield stress and slip plane in Fe₃Al_0.8Si_0.2 having the critical ordering temperature of the B2-DO₃ transformation T_c=1028 K were investigated at temperatures between 77 and 1100 K with respect to their dependence on temperature and orientation. A peak in the yield stress takes place at 880 K except in the crystal whose maximum resolved shear stress plane coincides with the twinning {112} plane. In the crystals which exhibit the peak in strength, the operative slip plane changes from {110} on which the antiphase boundary energy is lowest (below the peak temperature) to the maximum resolved shear stress plane (above the peak). The peak in strength is attributed to the Stoloff and Davies’ model based on the transition from superdislocations to imperfect dislocations below T_c. In the crystal exhibiting no peak, the yield stress is remarkably higher than that in the crystals exhibiting a peak, at temperatures between 350 and 880 K, where the operative slip plane is the twinning {112}. The yielding is related to the generation of imperfect dislocations.

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