The regularities of the thermal expansion of cladding tubes and rods from the E110opt alloy, as well as the anisotropy of their thermal properties in the case of layer-by-layer texture inhomogeneity are studied. The thermal linear expansion coefficients (TLEC) of rods and cladding tubes were measured in the axial, radial and tangential directions during heating and cooling in the temperature range of 293–1473 K (20–1200°C). It is shown that as a result of α → β → α phase transformations in the samples, a stable texture of phase transformations is formed which is preserved during subsequent heating and cooling cycles. Analytical expressions are obtained that describe the temperature dependence of the thermal expansion coefficient in the first cycle of heating products from the E110opt alloy, taking into account possible α → β phase transformations and the resulting α-Zr crystal lattice deformation along the a and c axes. It was established that the presence of layer-by-layer inhomogeneity in the samples leads to the appearance of stresses between layers with different crystallographic textures and, as a result, affects the orientation dependence of phase transformations that are sensitive to the stress state in the material. The results obtained indicate the need to take into account the internal stresses arising in textured anisotropic materials during heating and cooling, and to separate the contributions of thermal expansion and plastic deformation when analyzing data from dilatometric measurements of sample sizes..

Regularities of Thermal Expansion of Cladding Tubes and Rods Made of E110opt Alloy within the Temperature Range of 273–1473 K (20–1200°C)

This article described the protective properties of Cr coatings with a barrier layer composed of ZrO2/Cr multilayers deposited onto E110 zirconium alloy. The coatings with a ZrO2/Cr multilayer thickness of 100, 250, and 750 nm and single-layer (1.5 µm) ZrO2 barrier were obtained by multi-cathode magnetron sputtering in Ar + O2 atmosphere. Then, cracking resistance and oxidation behavior were studied under conditions of thermal cycling (1000 °C) in air and high-temperature oxidation at 1200–1400 °C in a water steam. The role of the ZrO2/Cr multilayers and multilayer thickness on cracking resistance of the experimental coatings and oxidation resistance of the coated E110 alloy was discussed. It was shown that the coatings with more quantity of the ZrO2/Cr multilayers have higher cracking resistance, but such types of samples have a large amount of coating spallation under thermal cycling. The high-temperature steam oxidation (1200–1400 °C) demonstrated that interfaces of the ZrO2/Cr multilayers can act as a source of cavities formed by the Kirkendall mechanism that results in accelerating Cr–Zr interdiffusion for Cr-coated E110 alloy. 

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Protective Cr Coatings with ZrO2/Cr Multilayers for Zirconium Fuel Claddings

Zirconium remains the main structural material for thermal reactors due to the small capture cross section of thermal neutrons. In the period of stricter safety requirements for reactors with a simultaneous increase in operating parameters, predicting the behavior of the material in emergency situations has gained greater urgency. In this work, we measured the temperature dependence of the thermal expansion of samples cut from thick-walled tubes made of Zr-2.5% Nb alloy that were deformed and annealed in different modes. The analysis of the physical processes responsible for the shaping of the material is carried out. It was found that the anisotropic change in the linear dimensions of cubic samples both during heating and cooling is due to a change in the zirconium content in the β-phase, phase transformations α + β-Zr → α + β-Nb → β → α + β-Zr, as well as the preferred orientation of the grains of the α-phase, characterized by high anisotropy of linear expansion. It is shown that the expansion of the investigated samples upon heating in the α -phase is determined exclusively by the integral texture parameters of Kearns, and the coefficients of thermal linear expansion (TLEC) in different directions vary over a wide range from 3⋅10-6 to 12⋅10-6 K−1. During cooling at the stage of the reverse phase transformation of the β-phase into α, an increase in the size of the cubic samples in the tangential direction up to 2.3 % and a decrease in the radial direction to 1.3 % are noted, which is associated with the orientation of the α-phase grains formed during cooling in the β -matrix and anisotropy of the TLEC of the α -grains. It is shown that the orientation of the α-phase grains in the reverse β → α transformation is determined not only by the orientation of the basal axes in the initial material, but also by the spatial distribution of the prismatic axes relative to the external directions in the tube. Significant size fluctuations in different directions of the samples obtained using the technology of manufacturing channel tubes for CANDU reactors should lead to the development of significant macrostresses both during heating and cooling of the tube. The structural state of the samples deformed or annealed at 400–530 °C does not significantly affect the temperature dependence of the TLEC, but is manifested only in some of its features. In this case, completely recrystallized samples, i.e., with a recrystallization texture, in which the  2 - 0 > directions are oriented along the tube axis, are characterized by a significantly lower variation in dimensions in different directions in the temperature range 20–1200 °C.

Influence of the structural state and crystallographic texture of Zr-2.5% Nb alloy samples on the anisotropy of their thermal expansion

Effect of the Stressed State on the Phase Transformations in Zirconium-Based Alloys

The temperature dependences of the periods a and c of the crystal structure of a-Zr and thermal linear expansion coefficients (TLEC) of textured cladding tubes and rods of E110opt Zr-based alloy in the axial direction in the temperature range of 293-873 K (20-600 °С) were determined. On the basis of Kearns’ integral texture parameters for cladding tubes and rods, TLEC values were calculated. The calculated values of the TLEC turned out to be significantly smaller than the values measured by the dilatometric method. Simulation of the process of thermal expansion of goods showed that the observed differences in the calculated and measured values of the TLEC can be due to layer-by-layer texture inhomogeneity of tubes and internal stresses arising between the layers.

Thermal expansion of cladding tubes and rods made of Zr-1% Nb alloy in the temperature range 293-873 K (20-600°C)based on X-ray and dilatometric measurements

https://iopscience.iop.org/article/10.1088/1757-899X/1005/1/012009/pdf

Features of creating wear-resistant anti-corrosion coatings with a barrier layer on fragments of fuel claddings from E110 o.ch.

the laws governing the formation of the properties of products. The anisotropy of plastic and strength properties of rolled zirconium alloys during tensile tests manifests itself in the different course taken by the process of deformation of specimens cut at various angles to the rolling direction. The action of plastic strain mechanisms is coupled with the regular reorientation of the grains of the specimen tested, as a result of which is the initial rolling texture. It is desirable to establish a correlation between the parameters of the stress--strain curve, recorded when the specimens are tested under tension in various directions, and the stability of their initial texture as well as to establish the distinction features in the changes in this texture during the testing. This correlation will make it easier to ascertain the causes of the anisotropy of the properties of products made of zirconium alloys and to develop methods of controlling this anisotropy. Experimental Procedure The specimens were made from cold-rolled tubing of Zr-l% Nb alloy with a diameter of 13.6 mm and a wall thickness of 0.9 ram. The tubing was cut along the generatrix and was straightened out. Tensile test specimens were cut from the resulting strips transversely and at 45 ~ to the rolling direction. The working part of the specimens measured i0 x 2 x 0.9 mm (series a) and 16 x 8 x 0.9 mm (series b). To remove the residual stresses which had arisen during the fabrication and straightening of the tubing the specimens were annealed at 500~ for 3 h in the presence of a getter in a sealed quartz ampul previously pumped down to 1.3.10 "a Pa. The specimens were tensioned in an Instron universal machine at a strain rate of 1.510 -4 sec -~. Longitudinal, transverse, and diagonal specimens of series a were loaded to breaking during recording of the load-extension diagram. The tensile diagrams obtained were replotted in the coordinates stress (o)--unit strain (~). The longitudinal and transverse specimens of series b were loaded until residual strains ~n of 6, 9, ii, and 4, 8, 12% were attained. The residual strains of the specimens of series b correspond to various segments of the stress~strain curve obtained on specimens of series a until necking occurred. The working part of the strained specimens of series b was cut out and subjected to x-ray examination in a DRON-I.5 diffractometer with CuK~ radiation.

V.V. Novikov

Papers

Thermal expansion of cladding tubes and rods made of Zr-1% Nb alloy in the temperature range 293-873 K (20-600°C)based on X-ray and dilatometric measurements

Regularities of Thermal Expansion of Cladding Tubes and Rods Made of E110opt Alloy within the Temperature Range of 273–1473 K (20–1200°C)

Features of creating wear-resistant anti-corrosion coatings with a barrier layer on fragments of fuel claddings from E110 o.ch.

Influence of texture on plastic tensile strain of rolled Zr-1% Nb alloy