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[en] The article reports studies of the Vickers and Knoop microhardness of α-zirconium (containing 500-700 ppm O2) using monocrystals and polycrystalline samples having a preferred orientation. These studies show inter alia that: 1) in Vickers measurements the Meyer index varies only slightly as function of the angle α between the normal to the plane of measurement and the x-axis of the basic crystallographic structure. 2) in Knoop measurements the hardness is practically independent of the load applied and it is possible to derive a plot of the Knoop hardness as function of the angle α and the direction of measurement in each crystallographic plane. In the case of polycrystalline samples, measurement of the Knoop hardness is sufficient to determine the position of the c-axis of the equivalent monocrystal characterising the texture of the material. (C.J.O.G.)
[en] Three kinds of Fe-based model alloys, Fe–0.018 atomic percent (at.%) Cu, Fe–0.53at.%Cu, and Fe–1.06at.%Cu were irradiated with 2 MeV electrons up to the dose of 2 × 10−5 dpa at 250 °C. After the irradiation, the increase in Vickers hardness and the decrease in electrical resistivity were observed. The increase in hardness by electron irradiation is proportional to the product of the Cu contents and the square root of the electron dose. The decrease in electrical resistivity is proportional to the product of the square of Cu contents and the electron dose. Cu clustering in the materials with electron irradiation and thermal aging was observed by means of the Atom Probe Tomography (APT). The change in Vickers hardness and electrical resistivity is well correlated with micro-structure evolution related to the Cu clustering process. The irradiation hardening was proportional to the square root of volume fraction of the Cu clusters from early stage of irradiation
[en] The indentation hardness, Vickers hardness, fracture toughness, and Young's modulus of polycrystalline uranium mononitride (UN) at sub-microscale and macroscale were evaluated by an indentation test, Vickers hardness test, and the ultrasonic pulse echo method. The Young modulus and Vickers hardness were in good agreement with the literature values. The fracture toughness of UN was about three times that of UO2. In addition, we revealed the indentation size effect on the indentation hardness of UN
[en] Ion irradiation experiments are useful for investigating irradiation damage. However, estimating the irradiation hardening of ion-irradiated materials is challenging because of the shallow damage induced region. Therefore, the purpose of this study is to prove usefulness of nanoindentation technique for estimation of irradiation hardening for ion-irradiated materials. SUS316L austenitic stainless steel was used and it was irradiated by 1 MeV H+ ions to a nominal displacement damage of 0.1, 0.3, 1, and 8 dpa at 573 K. The irradiation hardness of the irradiated specimens were measured and analyzed by Nix–Gao model. The indentation size effect was observed in both unirradiated and irradiated specimens. The hardness of the irradiated specimens changed significantly at certain indentation depths. The depth at which the hardness varied indicated that the region deformed by the indenter had reached the boundary between the irradiated and unirradiated regions. The hardness of the irradiated region was proportional to the inverse of the indentation depth in the Nix–Gao plot. The bulk hardness of the irradiated region, H0, estimated by the Nix–Gao plot and Vickers hardness were found to be related to each other, and the relationship could be described by the equation, HV = 0.76H0. Thus, the nanoindentation technique demonstrated in this study is valuable for measuring irradiation hardening in ion-irradiated materials
[en] The effects of manufacturing thermal cycle on the various mechanical properties of CuCrZr were investigated. Vickers hardness was changed with an aging temperature in an identical manner with the strength change in a wide range of heat treatment. The change of Charpy impact energy with an aging temperature exhibited an opposite trend to the changes of the strength and hardness. At least in terms of the impact energy of CuCrZr, aging at a higher temperate would be preferable if the strength of CuCrZr could be maintained higher than the limitation value after the completion of the fabrication of ITER first wall. The fatigue life of CuCrZr was influenced to a certain extent by the cooling rate and the aging temperature. Especially in the higher strain amplitude, the contribution of the elastic and plastic components to the fatigue response was dependent on the yield strength which is determined by the aging temperature.
[en] A monometallic V–4Cr–4Ti thermal convection loop was run for 2355 h with a peak temperature of 700 °C (973 K) and Li flow rate of 2–3 cm/s. Specimens of V–4Cr–4Ti exposed in the hot and cold legs of the loop and tensile tested in vacuum at 500 °C (773 K) showed an increase in the 0.2% yield and ultimate tensile strengths and a decrease in the serration amplitude with decreasing exposure temperature in the loop. However, only minor changes in ductility were measured. With the higher temperature exposures, a decrease in Vickers hardness was measured, but little change in the grain size was observed. Characterization of the microstructure after exposure at 627 °C (900 K) in the loop showed an increase in the density of Ti- and N-rich grain boundary and matrix precipitates near the specimen surface after exposure corresponding to an increase in the hardness in the near-surface region. Two-layer V/Y2O3 coatings on V–4Cr–4Ti substrates also were exposed in the loop, and initial room temperature characterization was conducted
[en] The irradiation hardening behavior of reduced-activation ferritic steels after single Fe-ion beam irradiation and dual-ion (Fe ion and He ion) beam irradiation experiments was investigated with nanoindentation tests. The ion-irradiation experiments were conducted at 563 K with 6.4 MeV Fe3+ ions up to 3 dpa at a 600 nm depth from the irradiated surface. Furthermore, these experiments were conducted with and without simultaneous energy-degraded 1 MeV He+ ions up to 300 appm. The materials used were F82H, F82H + 1Ni, and F82H + 2Ni to investigate the effect of Ni addition on the irradiation hardening behavior. The measured nanoindentation hardness was converted to the bulk-equivalent hardness based on a combination of the Nix–Gao model to explain the indentation size effect and the composite hardness model to explain the softer substrate effect of the nonirradiated region beyond the irradiated depth range. It is clearly shown that the Ni addition enhances the irradiation hardening of F82H. The bulk-equivalent hardness is compared with the experimentally obtained Vickers hardness of F82H steels after neutron irradiation. The effect of simultaneously implanted helium on the irradiation hardening is negligible in the investigated irradiation conditions
[en] Creep rupture life and microstructural degradation have been studied in two heats of Gr.91 steels. The coarsening of subgrains and precipitates, mainly M23C6 and MX, has been evaluated during static aging and creep. Hardness of head (static aging) and gauge (creep) portions of crept samples were measured to know their relation with microstructural degradation during long-term exposure. The correlation between subgrain size and spacing of precipitates and hardness has been equated. As an example, there is a close correlation between hardness value and inverse subgrains size in Gr.91 steels, regardless of aging or creep conditions. The appearance of three recovery mechanisms was found during long-term creep, namely: strain-induced recovery, pure static recovery and strain-assisted static recovery. By equated correlations between subgrain size, precipitates and hardness, the contribution of three recovery mechanisms to subgrain coarsening and hardness drop were calculated for two creep conditions at 700 °C in long-term creep region, where breakdown of creep strength has happen. The calculated data accord well with experimental data obtained from aged and crept samples. The contribution of static recovery to the subgrain coarsening and consequent hardness drop during long-term creep increases with increasing creep time. The significant contribution of both static recovery mechanisms can result in the breakdown of creep strength in long-term creep region
[en] Highlights: • Examination of the structure and phase stability of an aged Pu–0.27 wt.% Ga alloy. • The Ga content appears sufficient to retain the δ-Pu phase at ambient temperature. • Tenuous stability of the δ-Pu phase when cooled to sub-ambient temperatures. • The alloy transformed to more than 40% α-Pu when cooled to −50 °C for 1 h. • The alloy appears to have undergone δ → α′ transformation during hardness indentation. - Abstract: This paper describes the characterisation of a naturally aged Pu–0.27 wt.% Ga alloy 35 years of age. The alloy was subjected to bulk chemical analysis, density determination, differential scanning calorimetry (DSC), optical microscopy, electron probe micro-analysis (EPMA) and hardness measurements. Despite the Ga content being only 0.27 wt.%, it nevertheless appears to be sufficient to retain the alloy in the δ-Pu phase at ambient temperature. This was demonstrated by optical microscopy, density measurements and DSC. However, the ambient temperature stability of the δ-Pu phase is tenuous. This was demonstrated by the propensity of the alloy to undergo transformation to α-Pu when cooled to sub-ambient temperatures. Indeed, both density measurements and DSC indicate that when the alloy is cooled to −50 °C for 1 h the alloy has transformed to more than 40% α-Pu. Moreover, a comparison of the Vickers hardness (expressed as a mean pressure) with transformation pressures for Pu–Ga suggests that the alloy has undergone δ → α′ transformation during the indentation process
[en] Highlights: • Linear and square superposition hardening models are compared for ion-irradiated metal. • Average density of dislocations and defects is considered for the hardening model. • Results of square superposition hardening model match better with experimental data.