Cu-Sn固溶体合金の高温定常変形

Strong obstacles can greatly impede the motion or transmission of dislocations, which can be reflected by strain rate sensitivity and activation volume. In this study, the strain rate sensitivity and activation volume of overaged Al-Zn-Mg-Cu alloys with a grain size of 3.1 μm fabricated by powder metallurgy were measured by two different methods: a stress relaxation test and strain rate jump test. It was found that the former method gave much higher strain rate sensitivity values. After reviewing the conventional theory of stress relaxation test, it is unreasonable that the activation volume at each cycle during the stress relaxation test is a constant. At a strain rate higher than 10−5 s−1, ∂lnε˙/∂τ*, which is proportional to the activation volume in the conventional theory of the stress relaxation test, increases significantly, and nearly linearly increases with the strain rate in its logarithmic form, while at a strain rate lower than 10−5 s−1, the value of ∂lnε˙/∂τ* is nearly a constant. The grain boundary sliding mechanism was incorporated into the plastic deformation during the stress relaxation test, and the strain rate sensitivity and activation volume obtained by stress relaxation after modification agree well with that obtained by the strain rate jump test.

Experimental study on rate dependence of macroscopic domain and stress hysteresis in NiTi shape memory alloy strips

The as-cast 40CrNiMo alloy steel with uniform microstructure is obtained through vacuum casting by using metal mold. The hot deformation behavior of as-cast 40CrNiMo alloy steel is investigated by isothermal compression tests. The Arrhenius constitutive model and processing maps of as-cast 40CrNiMo alloy steel are constructed. The results indicate that the true stress–strain curves present typical dynamic recovery type under low deformation temperature and high strain rate. With the increases in deformation temperature or the decreases in strain rate, the true stress–strain curves gradually transform to dynamic recrystallization type. Through the analysis of processing maps and microstructures, it can be found that the area of plastic instability increases with the increase in the strain and gradually expands to the region of high deformation temperature and low strain rate. The deformation temperature range of 850-1050 °C and strain rate range of 0.001-0.01 s−1 are recommended as the reasonable hot-working process conditions. Results of this research can provide references for the selection of process parameters in casting–forging combination forming of 40CrNiMo alloy steel.

This paper describes the use of the Dynamic Shear Rheometer (DSR) to characterise the steady-state shear deformation properties of two grades of bitumen over a wide range of stresses and strain rates. The steady-state shear strain rate has been used to characterise the quasi-static deformation behaviour of the bitumen. Results indicate that at low levels of shear stress the behaviour of the bitumen is linear whereas at higher levels of shear stress the behaviour is non-linear. A simple model has been developed to compare results from the DSR test to results that would be obtained from a test with uniform shear stress and shear strain rate conditions. The model assumes linear behaviour at low stress levels (<50 kPa) and power law creep behaviour at high stress levels (>100 kPa). Between these two stress levels there is a transition region where the behaviour changes from linear to power law creep. A power law creep exponent of n =2.4 was used for both bitumens. Results from the model show reasonably good agreement with the experimental data over the range of stress levels and strain rates tested. Results also indicate that the effect of the non-uniform shear stress and shear strain rate conditions in the disc shaped samples used in the DSR test does not significantly effect the degree of non-linearity, although the viscosities determined in the non-linear region will be higher than the viscosities obtained under uniform shear stress/strain rate conditions.

Influence of TiN nanoparticles on the microstructure and properties of W matrix materials prepared by spark plasma sintering

The behaviour of energetic solids subjected to simple shear loading is modelled to predict ignition. The model is transient, one dimensional and includes effects of thermal diffusion, plastic work and exothermic reaction with one-step irreversible Arrhenius kinetics. A common power-law constitutive model for shear stress which accounts for strain hardening, strain-rate hardening and thermal softening is used. For the energetic solid composite LX-14 subjected to an average strain rate of , the model predicts reactive shear localization after an induction time of approximately t=5 ms, in which regions of high strain rate () are confined to thin spatial zones. An approximate thermal explosion theory which enforces spatially homogeneous stress, temperature and reaction progress as well as accounting for the early-time dominance of plastic work over exothermic reaction allows the development of simple analytic expressions for the temporal evolution of all variables. The simple expressions give predictions which agree well with both: (a) numerical predictions of a spatially homogeneous theory which allows simultaneous influences of reaction and plastic work and (b) numerical predictions of a spatially inhomogeneous theory which accounts for spatial stress distributions, thermal diffusion and spatially localized reaction. In particular, the induction time to ignition is captured accurately by the approximate theory; hence, while reactive shear localization may accompany an ignition event, ignition causality is most dependent on plastic work done during the time of spatially homogeneous shear.

Anomalous high temperature strengthening in concentrated α titanium-aluminum alloys

The performance of Zr1NbSnFe alloys within the range of Sn 0–0.65 % and Fe 0.03–0.35 % were studied through irradiation of fuel rods in two pressurized water reactors (PWRs) operating with significantly different fuel management strategies. Material test rod irradiations have also been launched in order to determine irradiation growth and corrosion behaviour on tubes irradiated under conditions representative of guide tubes. Results show that the increase in tin content up to 0.3 % does not significantly change the corrosion resistance nor the hydrogen pick-up compared to Zr1Nb alloy, while ensuring a higher creep resistance and an improved dimensional stability. On the contrary, at 0.5 % Sn, the corrosion resistance can be significantly degraded under demanding conditions. The iron addition to the alloy can be considered as a second order parameter for both corrosion and creep properties.

The performance of Zr1NbSnFe alloys within the range of Sn 0–0.65 % and Fe 0.03–0.35 % were studied through irradiation of fuel rods in two pressurized water reactors (PWRs) operating with significantly different fuel management strategies. Material test rod irradiations have also been launched in order to determine irradiation growth and corrosion behaviour on tubes irradiated under conditions representative of guide tubes. Results show that the increase in tin content up to 0.3 % does not significantly change the corrosion resistance nor the hydrogen pick-up compared to Zr1Nb alloy, while ensuring a higher creep resistance and an improved dimensional stability. On the contrary, at 0.5 % Sn, the corrosion resistance can be significantly degraded under demanding conditions. The iron addition to the alloy can be considered as a second order parameter for both corrosion and creep properties.

Thin films of tin‐doped , with different tin contents produced by a powder pyrolysis technique have been investigated by x‐ray absorption spectroscopy and x‐ray diffraction. At the indium K‐edge, extended x‐ray absorption fine structure (EXAFS) investigations reveal that the indium atomic environment is modified by the doping. Even at low tin concentrations, the first oxygen polyhedron and the metallic In‐In coordination shells are disordered. This disorder increases with increasing tin content, and, for a large tin content (39% Sn), the In‐O shell is locally similar to that of the hexagonal high pressure phase of , that is also known to be stabilized at atmospheric pressure by the insertion of small foreign cation (such as Sn4+) in the indium oxide structure. The x‐ray diffraction experiments also support the idea of a disordered network; the x‐ray reflections decrease in magnitude but remain sharp even for a high tin concentration. This indicates that the structural disorder observed by EXAFS only induces a damping of the x‐ray reflections (the network is still ordered within large domains). The following modifications of the host network were observed; an increase in the lattice parameter, a decrease in the size of coherence of the diffraction domains with increasing the tin content (from 1200 Å to 700 Å), and a <100> preferential orientation, which disappears for the high dopant concentrations.

The Mossbauer spectra of 119Sn in binary glasses of SnO and SiO2, in varying proportions of between 16.8 and 71.5 mol% SnO, have been obtained at 77 K. From these spectra the tin was found to be predominantly in the 2+ state. The isomer shift and the quadrupole splitting were both significantly greater than those in crystalline SnO and were found to decrease with increasing tin content, which also corresponds to decreasing molar volume. A second series of spectra of two of the samples was taken at temperatures between 10 and 300 K. These spectra show a decrease in shift with temperature which was the same for the two samples and which could only partly be accounted for by the second-order Doppler shift. The remainder was ascribed to the temperature dependence of the isomer shift. By using these data together with the measured expansivity and increase in density with tin content, it was possible to correct the isomer shift for the effects of the change in volume, and it was found that the volume-corrected isomer shift increased with increasing tin content. This showed that there was an increase in s-electron density at the tin nuclei, while the accompanying decrease in quadrupole splitting showed a decrease in the p-electron character, as expected for a decrease in covalency. From the decrease in absorption area with temperature the Debye temperature of tin was estimated to be ~190 K, which is slightly less than that of crystalline SnO, and decreased with increasing tin content. All the data suggest that the Sn-O bonds become progressively less covalent as more tin is added to SnO-SiO2 glasses, and possibly indicate a change from 4-fold to 6-fold co-ordination. A third series of spectra was obtained for the glass containing 40.9 mol% of SnO after a series of heat treatments. The spectra show changes in the oxidation state of the tin which depended upon the different conditions applied.

Observations of time effects in triaxial compression tests performed on crushed coral sand with constant strain rate, creep tests at different stress levels, and stress relaxation tests initiated at different stress levels are presented. The classic time effects found in most materials, i.e. increasing stiffness and strength with increasing strain rate and corresponding creep and stress relaxation behavior, are not observed in sand. Observations from the experiments show that strain rate effects are negligible for crushed coral sand, unlike for clays in which strain rate effects are significant. Further, the observed stress relaxation behavior was not in &amp;ldquo;correspondence&amp;rdquo; with the measured creep behavior. Therefore, the amount of stress relaxation predicted on the basis of model parameters determined from creep experiments is too small. It is concluded that sands do not exhibit viscous effects, and their behavior is indicated as &amp;ldquo;nonisotach,&amp;rdquo; while typical behavior of clay is termed &amp;ldquo;isotach.&amp;rdquo; Thus, there are significant differences in time-dependent behavior patterns of sands and clays. In another investigation on Antelope Valley sand the measured responses in creep and stress relaxation tests and in constant strain rate tests exhibited similar behavior as the crushed coral sand but with smaller discrepancy between the creep and stress relaxation tests. An explanation for these non-viscous and dissimilar effects for different sands is proposed and relates to the amount of grain crushing that occurs in different sands.

Copper-2.5 at%Al alloy single crystals oriented for a single slip system were deformed in tension at 600 and 700°C. In the later stage of deformation, the condition of steady state deformation was satisfied; namely the specimens have been deformed at a constant stress, independent of strain. In this steady state deformation stage, the internal stress and the effective stress were determined by the stress dip test. The dislocation substructure formed in this stage were observed by the etch pit technique. The results obtained are as follows:(1) The tensile axis rotated into the direction predicted by the single glide on the (111)[\bar101] slip system. When the tensile axis approached the [001]-[\bar111] symmetry line, the steady state deformation was observed.(2) The strain rate is proportional to the nth power of the steady state stress and the n value is about 5.(3) The ratio of the internal stress to the applied stress is 0.6∼0.9 and depends on the applied stress. The effective stress increases with the applied stress.(4) The parameter m* describing the effective stress sensitivity of dislocation glide velocity was estimated assuming the mobile dislocation density to be proportional to the square of the applied stress and the m* value was found to be 1.1.(5) The subgrains elongating in the [1\bar21] direction are found on the (111) plane. On the (1\bar11) plane the rows of dislocations are found along the direction roughly parallel to the trace of the primary slip plane, and the high dislocation density regions, approximately perpendicular to the slip trace, are observed.

Tin-doped indium oxide (ITO) samples with doping level up to 12.3 at% Sn were prepared by a sol-gel technique and characterised by X-ray powder diffraction as well with ^(119)Sn-Mossbauer spectroscopy. Diffraction patterns indicated that all samples were cubic, space group Ia-3, and isostructural with In_2O_3. Diffraction lines were broadened, the line broadening increased with tin content. The unit-cell parameter increased with tin doping level up to 7.8 at% Sn and decreased at higher levels. This behaviour of the unit-cell parameter indicated that the tin substitution for indium on B and D sites of the original In_2O_3 structure is non-uniform and depends on tin content. Rietveld structure refinement showed the presence of interstitial oxygen in the Sn-doped samples. The position of interstitial oxygen indicated the D site preference for tin at low tin doping level, and subsequent increase in the B site occupancy with the increase in tin content. ^(119)Sn-Mossbauer spectroscopy revealed that incorporated tin resided equally sites B and D for 7.8 at% Sn. Below that doping level the preference for tin to occupy D site was noticed, while for doping level higher than 7.8 at% Sn the B site was preferred.

Based on the previous result that the steady state deformation is observed in the Sendust single crystals, deformation behaviors of Sendust polycrystals were investigated in compressive tests at various temperatures and strain rates.The steady state deformation occurs at high temperatures and low strain rates. Under the conditions, the strain rate is represented by the relationship of \dotε=Bσnexp(−Q⁄kT), where n=4.3 and Q=360 kJ/mol. Compared with the values obtained on Sendust single crystals, n is nearly equivalent but Q is considerably lower. Sendust polycrystals can be plastically compressed to high strain under the conditions where the steady state deformation occurs. After the deformation, fine recrystallized grains are formed at original grain boundaries, and sub-boundaries and dislocation networks are observed within original grains. The steady state deformation of Sendust polycrystals is controlled by grain boundary sliding, grain boundary migration and dynamic recrystallization. On the contrary, the steady state deformation of Sendust single crystals can be explained in terms of the recovery-controlled mechanism.