Yasuhiro Higashiguchi

The inhomogeneous deformation behaviour of neutron irradiated Zircaloy-2

Annealed Zircaloy-2 specimens irradiated to 3.2 × 1019 n/cm2 (E > 1 MeV) at ≈425 K were tensile-tested, together with unirradiated material, between 298 and 673 K in vacuum. The surface and microstructure of deformed specimens were observed using projector, optical and transmission electron microscope. Metallographie examinations or irradiated samples showed that localized deformation bands occur at intervals during deformation to the ultimate tensile stress between 473 and 623 K, while in the room temperature deformation, the inhomogeneity in metallographic features was characterized by microscopic dislocation channeling structure, without showing localized band on the surface of deformed specimen. From the shape of the stress-strain curves and metallographic features, it was concluded that the first localized band occurred after a small amount of strain, resulting in yielding and that the flow stress increased monotonically with further yielding. Evidences from temperature dependent mechanical properties of irradiated and unirradiated samples indicate that the radiation-anneal hardening phenomena are of significance in a range of temperature at which localized bands are formed, particularly pronounced at 553–593 K.

Effects of neutron irradiation on SiC fiber

Abstract Two types of SiC fibers, SiC(1000) and SiC(1300), were irradiated with JMTR and RTNS-II. The SiC(l000) fiber is amorphous SiC, and the SiC(1300) fiber is macrocrystalline β-SiC. Tensile strength. Youngs modulus and X-ray radial distribution function (RDF) of both the SiC fibers irradiated at 4 × 10 17 n/cm 2 with RTNS-II ( E = 14 MeV ) were not different from the unirradiated state. In both the SiC fibers, when irradiated with JMTR ( E > 1 MeV ), the tensile strength and Youngs modulus increased gradually with the neutron fluence. RDFs of both SiC fibers irradiated at 1 × 1019 and 2 × 10 19 n/cm 2 with JMTR showed that the atomic configuration was disordered by irradiation. It appeared that the SiC fibers were influenced in mechanical properties and atomic arrangement by neutron irradiation. The mechanical properties of neutron-irradiated SiC fibers are compared with those of neutron-irradiated carbon fibers.

Mechanical properties of neutron irradiated SiC fibers

SiC fibers were irradiated at neutron fluences of 8 × 10 23 and 2 × 10 24 n/m 2 in JMTR ( E >1 MeV). The tensile strength of SiC fibers measured at gauge length of 5 mm essentially unchanged after the neutron irradiation, but the strength at a length of 25 mm and 50 mm increased by 40% and 25% after the irradiation, respectively. The tensile strength variations of the irradiated SiC fibers with respect to gauge length were examined in terms of Weibull statistics. The Weibull modulus of the tensile strength in the SiC fibers increased slightly by the neutron irradiation. SiC fibers and SiC fiber reinforced aluminum preform wires (SiC/Al) were irradiated in JOYO ( E > 0.1 MeV) at neutron fluences of 1 × 10 24 , and 1 × 10 24 and 1 × 10 25 n/m 2 , respectively. The mechanical properties of the irradiated SiC fibers and the SiC fibers extracted from the irradiated SiC/Al preform wires were essentially unchanged in comparison with the unirradiated SiC fibers.

Absorption and desorption behavior of hydrogen by neutron irradiated titanium

Abstract The hydrogen absorption and desorption behavior of the neutron irradiated titanium (Fluence: 6.2 × 10 20 0 n/cm 2 , E > 1 MeV) has been investigated in the temperature range of 450 to 650°C. The absorption and desorption rate equations were obtained as k a [ min −1 ] = 2.0 × 10 5 exp (−89.5[ kJ / mol ]/ RT ) and k d [min −1 ] = 58.7exp(−23.0[kJ/mol]/RT), respectively. The values of the absorption and desorption rate constants for the irradiated titanium are larger than the respective values for the unirradiated titanium while the values of the activation energy for the irradiated titanium are similar to the respective values for the unirradiated titanium. The excess hydrogen solubility is observed for the irradiated titanium.

Effect of fast-neutron irradiation on deformation twinning in zirconium deformed at 77 K

Abstract The effect of neutron irradiation on twinning deformation is investigated at 77 K using unirradiated and to a fluence of 4.1 × 1019n/cm2 irradiated zirconium. The slip line density Ns, the twin volume fraction Vt and the twin density Nt for both specimens were determined as a function of strain by means of optical microscopy. The twins were determined using the diffraction profiles of {1012} twins at the early stages, as well as, {1122} and {1124} twins at the latter stages of deformation. It is shown that the nucleation of twins was affected more strongly than the growth by neutron irradiation.

Microstructure and mechanical properties of neutron irradiated V-20Ti alloy

Abstract Neutron irradiation damage and its effects on mechanical properties were studied for V-20Ti alloy with three different fluences: 5 × 10 24 , 2 × 10 24 and 1× 10 23 n m -2 ( E > l MeV) , named A-, B- and C-specimens, respectively. Radiation-induced precipitates (RIP) were observed in A and B specimens and no voids in all specimens. It was clear from the detailed investigation that the precipitates are circular and planar coherent particles lying on (100) planes and have the fee structures. The mechanisms for suppression of void formation and for softening the irradiation effects on the mechanical properties were suggested based on the relation with radiation-induced precipitates (RIP) which were considered as a non-stoichiometric suboxide and contained many vacancies at lattice sites.

Effect of hydrogen on the mechanical properties at high temperature of fast-neutron irradiated Ti alloys

Abstract The effects of neutron irradiation on the mechanical properties were studied over a temperature range from 298 to 923K for three Ti alloys ; Ti-6.5A1, Ti-6A1-4V and Ti-15Mo-5Zr. The precipitation which occurred during heating of the specimens at the testing temperature strongly influenced the mechanical properties for all alloys. Only Ti-6. 5Al specimens of the three alloys were provided to the following examination which was tensile tested at 723K in a hydrogen atmosphere after absorption of hydrogen. The yield stress of the unirradiated specimens increased after hydrogen absorption. However, the yield stress of the irradiated specimens decreased rapidly with little hydrogen content and became lower than that of the unirradiated. This reason was considered to be the relation between the hydrogen absorption process and radiation defects.

Twinning deformation at room temperature of fast-neutron irradiated titanium

Abstract Effect of the neutron irradiation on the twinning deformation has been studied with unirradiated and irradiated titanium. An optical microscope was used to reveal the deformation modes at different strains and to obtain the twin volume fraction Vt and the twin density Nt as a function of strain. The value of Vt and Nt are larger in the irradiated specimens. A detailed study shows that the nucleation of twins is remarkably enhanced by irradiation, in agreement with the observation by transmission electron microscope. The twins are nearly all of {1012} system.

The improvement of irradiation-enhanced copper embrittlement in FeCu alloys

Abstract The effect of alloying elements on neutron irradiated FeCu alloys has been investigated in order to obtain the fundamental information on the irradiation-enhanced copper embrittlement for power reactor vessel steels. The mechanism of copper-induced irradiation embrittlement in the copper-containing iron alloys was proved to be due to both the interaction of copper atoms with irradiation-produced complex defects within grains, and the preferred grain boundary segregation of copper atoms existing near grain boundaries. The former effect causes the increase of yield strength, and the latter results in the ductility loss and grain boundary crackings. The addition of titanium up to 0.4 wt% to the Fe-0.1 wt% Cu alloy was found to be extremely effective in the improvement of both the irradiation-induced ductility loss and strength. Aluminum and silicon were not as effective as titanium.

Inhomogeneous plastic deformation and its relevance to iodine stress corrosion cracking susceptibility in irradiated Zircaloy-2 Tubing

Abstract Evidence from tensile tests on specimens derived from Zircaloy-2 tubing of current 8× 8 BWR type design and irradiated to 3.2 × 10 19 and 3.0 × 10 20 n/cm2 ( E > 1 MeV) showed that inhomogeneous plastic deformation occurred in the temperature range 300–350°C for the higher neutron fluence, but not for the lower one. Dislocation channelings were also identified by transmission electron microscopy for the specimen irradiated to the higher fluence and strained at around 320°C, but not for the lower fluence. On the basis of the results, an attempt was made to explain the influence of neutron irradiation on the iodine stress corrosion cracking (SCC) susceptibility of Zircaloy tubing, suggesting that a drastic increase of SCC susceptibility at neutron fluences above 1020 n/cm2, hypothesized by Lunde and Videm, could be successfully interpreted in terms of the occurrence of dislocation channels.