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[en] There is now a large number of sophisticated steels which rely on silicon as an alloying addition with the purpose of avoiding the precipitation of cementite. However, there is also evidence that the silicon can enhance the formation of ε-carbide; the mechanism of this effect is not understood and the absence of appropriate thermodynamic data makes it impossible to conduct calculations. We report here some ab initio calculations which throw light on both of these issues and suggest novel experiments.
[en] Segregation of silicon to the surface of Ni-12.7 at% Si alloys during 2.0-MeV He and 3.25-MeV Kr irradiations was measured using Rutherford backscattering spectrometry. For equal calculated defect production rates the Kr irradiation was <3% as efficient as the He irradiation for promoting segregation in the temperature range, 4500C-5800C. It was further observed that Kr preirradiation of specimens dramatically reduced segregation during subsequent He irradiation. A model for cascade annealing in Ni-Si alloys is presented which qualitatively explains the segregation results. The model assumes that small interstitial-atom-clusters form in individual cascades and that these clusters become trapped at silicon solute atoms. The vacancy thereby becomes the more mobile defect. The model should also have relevance for the observation that void swelling in nickel is suppressed by the addition of silicon solute. (orig.)
[en] The intergranular corrosion of Ni base alloys (Inconel 600) increase with their C content due to the interaction of this element with the defects of the grain boundaries. In contrast, the intergranular corrosion of Inconel 600 is not modified by an addition of 0.9%Si. This is due to the very high anodic dissolution speed of these alloys containing 16%Cr
[fr]La corrosion intergranulaire d'alliages hypertrempes du type Inconel 600 est fortement augmentee en presence de carbone qui interagit avec les defauts de reseau constituant les joints de grains. Par contre, l'addition de silicium jusqu'a 0,9% ne modifie pas la corrosion intergranulaire de ces alliages. Ceci est probablement lie a la vitesse de dissolution elevee des alliages a base de nickel ayant une teneur en chrome de l'ordre de 16%
[en] Measurements of the Auger Parameter for silicon in the interfaces exposed in oxidised Fe/Si alloys, when compared with similar measurements on standards, have provided valuable chemical information that is in agreement with theoretical predictions. (Author)
[en] In the present work, we studied the effect of minor Si addition on the magneto-caloric effect (MCE) of the Gd_5_0Co_5_0 metallic glass. The Gd_5_0Co_5_0_−_xSi_x (x=2, 5) as-spun ribbons show typical amorphous characteristics in structure and magneto-caloric behaviors. The peak values for the magnetic entropy change (−ΔS_m"p"e"a"k) of the Gd_5_0Co_5_0_−_xSi_x (x=0, 2, 5) metallic glasses increase significantly with the addition of Si. The mechanism for the enhanced MCE by minor addition of Si was investigated by revealing the relationship between −ΔS_m"p"e"a"k and the Curie temperature in the Gd-Co-based amorphous ribbons. - Highlights: • Minor Si addition enhances the −ΔS_m"p"e"a"k but decreases the T_c of the Gd_5_0Co_5_0 metallic glass significantly. • The Gd_5_0Co_5_0_−_xSi_x (x=2, 5) as-spun ribbons exhibit typical magneto-caloric behaviors of soft magnetic metallic glasses. • A nearly linear dependence of ln(−ΔS_m"p"e"a"k) on the ln(T_c"−"2"/"3) in Gd-Co-based amorphous ribbons was found.
[en] The effect of silicon and magnesium addition in a molten Al bath on the morphology and corrosion resistance of the Al coating layer of steel formed during hot-dip aluminizing was investigated at the temperatures of 700, 800, and 900 °C for the dipping time of 1-15 minutes. The thickness of the intermetallic layer decreased with an increasing Mg or Si content within a range of 0-1 at%. Addition of Si made the intermetallic layer thin whereas addition of Mg compensated for the decrease of the thickness significantly. The shape of the intermetallic layers became less irregular than that of the hot-dip aluminizing in pure aluminum. The results of immersion corrosion tests and electrochemical corrosion tests in a solution of 3 wt% NaCl showed that the corrosion resistance of the Al-1% Si-1% Mg coated steel had increased significantly over the Al coated steel. The open circuit potential changed from ‒0.56324 V (vs. SCE) to ‒0.48872 V (vs. SCE) and the corrosion current density decreased from 9.9991 µA/cm"2 to 2.1160 µA/cm"2. A salt fog spray test on these specimens also showed hot-dip aluminizing with Si and Mg addition increased the corrosion resistance significantly.
[en] The purpose of investigations consisted in evaluating the effect of silicon on the structure and properties of structural steels. Four model alloys of the similar carbon content and the variable Si content were tested. The tests include measurements of HV, Rg, Rg0.2 and KIc. It has been shown that in the quenched steels containing about 0.3%C, silicon in the range of concentration 0.48-1.15% does not affect the hindering of their hardness decrease of Si content from 0.48% to 1.15% causes a clear growth coefficients Rg and Rg0.2. When the plane strain reached (at -40 and -196 C) the fracture toughness (KIc) decreases slightly. (author)
[en] The experimental results of investigations of non-oriented steels after tensile deformation are reported. The steel samples were tested using the magnetovision method and the single strip tester. The applied deformation was up to 15% but the most significant changes were detected in the first step - at 0.5%. In several cases it was observed that after stress the homogeneity of the structure of the samples was destructed
[en] In the course of irradiation creep experiments on Ni-4 at.% Si alloy, two types of creep transients were observed on the termination of irradiation. The short term transient was completed within one minute while the long term transient persisted for nearly ten hours. A change in the temperature distribution was excluded from the possible causes, partly because the stress dependence of the observed transient strains was not linear, and partly because the strain increase expected from the temperature change was much smaller than the observed value. Transient behavior of point defects was examined in conjunction with the climb-glide mechanism and the steady-state irradiation creep data. Calculated creep transient due to excess vacancy flux to dislocations was in good agreement with the observed short term transient. The long term transient appears to be a result of dislocation microstructure change. The present results suggest an enhanced irradiation creep under cyclic irradiation conditions which will be encountered in the early generations of fusion reactors. (orig.)