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1.
The strain-rate cycling test during the Blaha effect measurement at 77–254 K was carried out for four kinds of single crystals: KCl doped with Mg2+, Ca2+, Sr2+ or Ba2+ as a weak obstacle. It was found that the critical temperature, at which the effective stress is zero, increases when the divalent ionic size approaches increasingly that of the K+ ion. Furthermore, the activation energy for the interaction between a dislocation and the divalent ion-vacancy dipole was determined. The activation energy increases with the divalent ionic size. Fleischer's model attributes this to the difference of tetragonality around the dipole for each specimen.  相似文献   

2.
A strain-rate cycling test during the Blaha effect measurement was carried out at 83–239 K for the purpose of studying the force-distance relation between a dislocation and the aggregate for KCl : Sr2+ (0.05 mol% in the melt) single crystals. On the basis of the dependence of strain-rate sensitivity due to the aggregates on temperature, it was found that the interaction between a dislocation and the aggregate in the specimen can not be approximated to the Fleischer's model taking account of the Friedel relation within the temperature. The square force-distance relation between a dislocation and an impurity seemed to be the most suitable model among the three: a square force-distance relation, a parabolic one and a triangular one, taking account of the Friedel relation for the specimen. In addition, the values of enthalpy and Gibbs free energy of activation for overcoming of the aggregate by a dislocation were obtained for the three force-distance relations.  相似文献   

3.
The interaction between a dislocation and the impurity in KCl : Mg2+ (0.035 mol% in the melt), KCl : Ca2+ (0.035 and 0.065 mol% in the melt) and KCl : Ba2+ (0.050 and 0.065 mol% in the melt) was investigated from the strain-rate cycling test during the Blaha effect measurement. This was carried out at 77–254 K. As a result, it was found that the Fleischer's model taking account of the Friedel relation seems to be suitable for KCl : Ca2+ and KCl : Ba2+. However, it was not appropriate for KCl : Mg2+. Furthermore, the values of T c, H(T c) and G 0 were obtained for the specimens. T c is the critical temperature at which effective stress is zero. H(T c) and G 0 are the enthalpy and the Gibbs free energy of activation for the breakaway of the dislocation from the impurity, respectively. H(T c) was almost the same for the specimens except KCl : Mg2+. G 0 increased with increasing the divalent cation size. In addition, the tetragonality around the divalent ion-positive ion vacancy pair was estimated on the basis of G 0 for the each specimen.  相似文献   

4.
It has been previously reported for KCl : Sr2+ (0.035, 0.050, 0.065 mol% in the melt) single crystals that the interaction between a dislocation and the impurity can be approximated to the Fleischer's model. From the values of 0 for the specimens, however, it was confirmed that the Friedel relation can be taken into the Fleischer's model. The 0 is the bending angle at which the dislocation embraces the impurities under the effective shear stress at 0 K. Furthermore, the interaction between a dislocation and the impurity could be approximated to the Fleischer's model taking account of the Friedel relation. This was examined on the basis of the dependence of strain-rate sensitivity due to the impurities on temperature at about 100–200 K. Then, the critical temperature, at which the effective shear stress is zero, was determined to be 282 K. In addition, the values of the enthalpy and the Gibbs free energy of activation for the breakaway of the dislocation from the impurity were obtained for the specimen.  相似文献   

5.
Single crystals of nominally pure KCl and KCl doped with Mg2+, Ca2+, Sr2+ or Ba2+ were deformed by compression at 77–254 K; during the tests strain-rate cycling was conducted in association with ultrasonic oscillation. The data were analyzed in terms of strain-rate sensitivity ((/ln)) versus stress decrement (). The curve for KCl doped with the divalent impurities has two bending points and two plateau regions. It is proposed that the variation of strain-rate sensitivity at the second plateau place on the curve with shear strain ((/ln)/) is due to a change in forest dislocation density with shear strain. The forest dislocation density for the specimens seemed to increase by the divalent additions in the compression test on account of the jogs on the screw dislocations. It depended on the concentration of impurities and also on the size of impurity in the specimens at a given temperature. Unfortunately, it was not possible to determine whether a change in the size of impurity influences mobile dislocation density, , from the values of / for KCl doped with Ca2+, Sr2+ or Ba2+.  相似文献   

6.
The strain-rate cycling test during the Blaha effect at 77–220 K has been carried out for three kinds of single crystals, KCI, KCI doped with Sr2+, and KCI doped with various impurities. The temperature and impurity dependence of the relation between strain-rate sensitivity and stress decrement, as well as the effective stress, p1, due to only one type of impurity lying on the dislocation with the largest separation, has been investigated. From the temperature dependence of p1, the force-distance profile between a dislocation and impurities was obtained. The critical temperature,T c, for KCI: Sr2+ was found to be about 227 K.  相似文献   

7.
A strain-rate cycling test during the Blaha effect measurement was carried out in stage I, II and III of stress-strain curve at 80–300 K. On the basis of the relation curve of strain-rate sensitivity and stress decrement due to oscillation, the influence of strain on the interaction between a dislocation and impurities was investigated for KCl : Li+ (0.5 mol% in the melt) and KCl : Na+ (0.5 mol% in the melt). It has been so far reported that the curve seems to reflect the influence of ultrasonic oscillation on the dislocation motion on the slip plane containing many weak obstacles such as impurities and a few strong ones such as forest dislocations. As a result, it seemed that the Na+ ions in KCl : Na+ contribute to dislocation multiplication in the three stages, whereas the Li+ ions in KCl : Li+ did not contribute to it. Furthermore, the effective stress due to the impurities decreased with increasing strain at almost all the temperatures for KCl : Na+. Accordingly, the critical temperature, at which the effective stress is zero, was larger in stage I, compared with that in stage II for KCl : Na+ from the dependence of effective stress on the temperature.  相似文献   

8.
A strain-rate cycling test during the Blaha effect measurement was carried out at 80–300 K for KCl:Li+ (0.5 mol % in the melt) and KCl: Na+ (0.5 mol % in the melt). We attempted to select the most suitable force-distance relation between a dislocation and the monovalent cation impurity among the three models, which are a square force-distance relation, a parabolic one, and a triangular one taking account of the Friedel relation the groping for the most suitable force-distance relation was conducted by following three relationships: the relation between effective stress and temperature, the dependence of strain-rate sensitivity due to the impurities on temperature, and the proportionality of H(T). The H(T) is the activation enthalpy for the interaction between a dislocation and an impurity as a function of temperature. As a result, the square force-distance relation seemed to be the most suitable of the three for KCl:Na+. However, it was difficult to select the most suitable relation of the three for KCl:Li+. Furthermore, on the three force-distance relations, critical temperature, Tc, and H(Tc) were obtained for both the specimens.  相似文献   

9.
The strain-rate cycling test during the Blaha effect measurement at 80 to 240 K has been carried out for two kinds of single crystals: quenched and annealed specimens of KCl:Sr2+. It was found that the force-distance profile, which expresses the interaction between a dislocation and impurities, cannot be approximated by the Fleischer's model when I–V dipoles turn into aggregates for KCl:Sr2+, and that the activation energy for the break away of a dislocation from impurities becomes small for the annealed specimen, compared with the quenched one. Furthermore, the critical temperature,T c, for the annealed KCl:Sr2+ is slightly smaller in comparison with that for the quenched one.  相似文献   

10.
Strain-rate cycling tests associated with ultrasonic oscillation were conducted at 80–239 K for two kinds of KCl:Sr2+ (0.05 mol% in the melt) single crystals: quenched and annealed specimens. Examining the relationship of temperature and dislocation velocity-effective stress exponent, m *, estimated from the data obtained in this series, we could find the suitable force-distance relation between a dislocation and the impurity. The force-distance relation for the quenched specimen approached to the Fleischer's model taking account of the Friedel relation rather than the Fleischer's model. As for the annealed specimen, the SQ was the most appropriate of the three models: the SQ, the PA, and the TR indicate a square, a parabolic, and a triangular force-distance profile respectively. The three force-distance relations are taken account of the Friedel relation. By annealing the quenched specimen, m * became low at a given temperature. This may have been caused by the following two phenomena. First, the concentration of weak obstacles to dislocation motion decreased after the heat treatment. Secondly, the resistance to movement of a dislocation in the quenched specimen was weakened by annealing it, e.g., F 0 was reduced to about one-third and 0 increased from 154 to 172 degrees. F 0 and 0 are the force acted on the dislocation and the bending angle of dislocation by the weak obstacle such as the impurity. Therefore, it may be deduced that the dislocation velocity in the quenched specimen is more sensitive to the effective stress due to the impurities than that in the annealed specimen at the temperature.  相似文献   

11.
12.
The wetting behavior of NiO single crystal by liquid aluminum has been studied by the sessile drop method under vacuum at 973–1273 K for 2 h. Optical microscopy, SEM, EDS and X-ray analysis were applied to characterize the structure and chemistry of solidified cross-sectioned sessile drop couples. Under tested conditions, molten Al wets and reacts with NiO to form Al2O3 and Ni. This leads to alloying of the initially pure Al drop with Ni to the hypereutectic composition and to the formation of a thick reaction product region inside the NiO substrate, whose structure presents interpenetrated networks of fine alumina precipitates and an Al–Ni matrix. After solidification the Al–Ni matrix and the drop have the same phase composition, which is in agreement with Al–Ni phase diagram, showing the formation of Al3Ni at T < 1128 K and Al3Ni2 at 1128 K < T < 1406 K. The strong reactivity of Al/NiO couples, accompanied with the drop deformation, fragmentation of the reaction product region and development of a crater under the drop, contributes to the perturbation of the triple line and to the formation of apparent contact angles at 1073–1273 K. This leads to unusual changes of measured contact angles with temperature, decreasing from 84° at 973 K to 36° at 1073 K, and then increasing to 75° at 1273 K, while structural analysis suggests complete wetting at 1073 K.  相似文献   

13.
14.
The thermoluminescence (TL) characteristics of KCl:Eu2+ irradiated with solar and monochromatic ultraviolet (UV) light have been investigated. The glow curves exhibit at least five TL peaks between room temperature and 673 K. The low temperature peaks (<500 K) are very sensitive to the UV radiation, but their intensities practically do not depend on the duration of solar irradiation and are determined by the ratio between the creation rate by UV and the bleaching rate by visible light. The high temperature 650 K peak is not so sensitive, but it is more stable under optical bleaching and its intensity increases supralinearly as exposure time increases. The creation spectrum of the 650 K peak presents a broad band with a maximum at 230 nm that extends in the long wavelength range at least up to 360 nm. The results obtained are discussed in relation to the development of a UV dosemeter with wavelength sensitivity dependence close to the action spectra of UV-related biological effects.  相似文献   

15.
Pure, Mg2+ and Zn2+ doped BTCC single crystals are grown from their aqueous solutions at 301 K. The grown crystals are characterized by single crystal XRD, FTIR and UV–Vis-NIR spectral studies. The preliminary investigations of the UV–Vis-NIR spectra on the doped samples suggest an increased percentage of transmission in comparison to pure BTCC crystals. The SHG efficiency of the metal doped BTCC crystals is found better than the pure ones. It is estimated from the microhardness studies that the mechanical strength of the BTCC crystals are improved due to the metallic (Mg2+ and Zn2+) substitutions.  相似文献   

16.
Mechanical Stress fields of nearly radial symmetry are produced by focused laser irradiation on (111) surfaces of copper single crystals. The dislocation structures in the vicinity of the heat-affected zone can be revealed with the aid of an etch pit technique. The observed etch pit pattern is in very good agreement with calculations based on dislocation theory.  相似文献   

17.
Interaction between a semi-circular cut on straight boundary and an edge dislocation, placed on the axis of symmetry, in a semi-infinite medium is investigated on the basis of Airy's stress function. The solution is constructed by considering the relation between the real edge dislocation and the imaginary one. Numerical calculations are worked out in some detail and these results are presented graphically in order to clarify the effect of above mentioned interaction.  相似文献   

18.
The thermoelastic stress developing during the growth of disk-shaped germanium single crystals for IR applications has been evaluated theoretically. The results have been shown to correlate with the dislocation structure of large germanium single crystals grown by the Stepanov method and directional solidification.  相似文献   

19.
Thermal glow curves of quenched KCl, both pure and doped with PbCl2, have been studied. Quenching from 650° C enhances the glow output by a much larger amount than can be explained on the basis of enhancement ofF-centre formation in quenched samples. Further, the glow peaks which are associated with divalent impurities and the first stage of colouration are also intensified by quenching. However, electrolytic colouration (which involves quenching) diminishes the integrated light output, when the coloured crystal is exposed to X-rays and warmed up. Heat-treatment of electrolytically coloured KCl crystals between 110 and 300° C induces a gradual increase of the colloid band at the cost of the existingF-band. In the case of KCl:Pb electrolysis producesF-band along with various forms of Pb (such as Pb0 and Pb); but subsequent heating does not produce colloid centres in this sample. On the basis of these results it is concluded that, (i) quenching increases emitting centres where electrons and holes recombine during thermoluminescence, (ii) recombination efficiency of electrons and holes may also increase due to quenching. A new peak at 285° C in the thermal glow curve of quenched KCl has been observed.  相似文献   

20.
A study is presented of the thermoluminescence (TL) of phosphors based on potassium halides doped with divalent lead, such as KCl:Pb2+, KBr:Pb2+ and the crystalline series KCl(1-X)Br(X):Pb2+. The defects in the crystals generated by irradiation have been investigated as well as the trapping and room temperature recombination mechanisms. The samples were gamma irradiated to a dose of 10 kGy. The TL spectral response during the recombination stage was obtained through simultaneous measurements of temperature, emitted light intensity and emission wavelength by using an automated thermoluminescence system with optical fibre couplings and a diode array as a detection device. The TL emission is a broad band in the 350-600 nm range with a maximum strongly dependent upon the mixed composition.  相似文献   

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