Commercial Pure Zirconium Research Articles

Окисление циркония, легированного хромом, при воздействии компрессионных плазменных потоков

The results of investigation of the zirconium structure on the first stage of oxidation at temperature 700 °C in the air atmosphere after 15 minutes are presented. The commercial pure zirconium alloy as well as zirconium alloyed with chromium atoms by means of compression plasma flows impact are investigated. The results showed the possibility to form the top layer in zirconium alloyed with chromium when a thin chromium coating (1 mm) was deposited on the surface and the compression plasma flow with the absorbed energy density 25 – 43 J/cm2 influenced. Due to alloying with chromium, the high-temperature β-phase of zirconium is stabilized at room temperature as β-Zr(Cr) solid solution and martensite α′-Zr phase is formed. The oxidation at temperature 700 °C demonstrated the higher oxidation resistance of the zirconium samples treated with compression plasma flows at the highest absorbed energy density 43 J/cm2. This regime modified the top layer of the zirconium sample without β-Zr(Cr) solid solution formation which enhances the oxygen diffusion.

Microstructures and Mechanical Properties of a Commercial Pure Zirconium during Rolling and Annealing at Different Temperatures

Rolling and annealing are important processes for the fabrication of zirconium alloy sheets. Herein, the microstructure and mechanical properties of a commercial pure zirconium during rolling and annealing at different temperatures are investigated. Compared with rolling at room temperature (RT), liquid nitrogen temperature (LNT) rolling will cause more inhomogeneous deformation and higher dislocation density, which significantly influences the subsequent annealing. For a given rolling reduction, the higher dislocation density in the LNT‐rolled specimen causes faster recovery and recrystallization and leads to larger average grain size in subsequent annealing compared with that in the RT‐rolled specimen. The inhomogeneous grain size may be attributed to the nonuniform deformation in the LNT rolling. Compared with RT rolling, higher yield strength is obtained in the LNT‐rolled specimen, which is caused by the suppression of dynamic recovery in low‐temperature deformation. With higher strength, the elongation of the LNT‐rolled specimen is not lower than that in the RT‐rolled specimen, which may be related to the inhomogeneous microstructure‐induced extra work‐hardening capability.

Characterization of shock-induced anomalous [formula omitted] twinning activity in a β-cooled zirconium

In this work, quasi-static compression and shock loading experiments were performed on a β-cooled commercial pure zirconium at room temperature to investigate the corresponding twinning behaviors, utilizing electron channeling contrast (ECC) imaging and electron backscatter diffraction (EBSD) technique. Results show that twins are introduced under both deformation conditions, while their fractions are quite different. The high strain rate during shock loadings facilitates the activation of twins, leading to a much larger fraction of deformation twins. Distinct from previous work, we report anomalous parallel 112¯1<1¯1¯26> twinning activities in the shock loading sample but not in the quasi-static compression one, implying that the facilitating effect of strain rate on such twinning mode might be more obvious in the present work. Based on Schmid factor calculation, the special grain orientations obtained by β slow cooling, together with the poor strain accommodation capacity due to suppressing prismatic slips, are responsible for the dense 112¯1<1¯1¯26> twins under shock loadings.

Deformation kinking in β-treated zirconium impacted by split Hopkinson pressure bar

In the present work, we report the observation of deformation kinking bands in β-treated commercial pure zirconium sheets during impact experiments. Crystallography analyses based on electron backscatter diffraction (EBSD) technique reveal that these kinking bands exhibit a common rotation axis of 〈101¯0〉 with misorientation angles varying in a wide range and are not belonging to anyone of the well-established twinning modes in Zr. Based on the combination of Schmid factor calculation and in-grain misorientation axes (IGMA) determination, the underlying mechanisms accounting for their formation are proposed and discussed.

Elevated Temperature Compression Deformation Behavior of Commercial Pure Zr Combined with the Constitutive Equation and Processing Map

The compression deformation behavior of commercial pure zirconium at elevated temperature is systematically investigated at different conditions. The corresponding deformation mechanism of pure Zr is clarified for analyzed flow stress, work hardening rate, activation energy, and microstructure. A modified Arrhenius‐type equation is proposed for future numerical simulation, which shows a good relativity between the theoretical and experimental data. The apparent deformation activation energy is 209 kJ mol−1, indicating that a cross‐slip of dominant dislocation mechanism controls the deformation process. Established based on the dynamic material model (DDM), processing maps indicate that the optimum processing conditions are 700–900 °C at 0.1–0.14 s−1 and 905–950 °C at 3–20 s−1 with the high efficiency of power dissipation. Microstructure examination reveals that the main restoration mechanism in the safe domain is related to dynamic recrystallization and the unstable regional microstructure results in the flow localization and cracking behavior.

Detwinning behavior in commercial pure zirconium during orthogonal re-compression after pre-compression and annealing

Twinning is an important plastic deformation mode for zirconium (Zr) and its alloys. Many researches have been carried out to investigate twinning related issues for Zr alloys. However, few study was reported on the detwinning in Zr alloys. In this work, pre-compression, orthogonal re-compression, and annealing were performed to investigate the deformation behavior of a commercial pure Zr (Zr702). Microstructure and texture evolution during deformation and annealing were examined by quasi-in situ electron backscatter diffraction (EBSD). It was found that {10–12} tensile twins were activated during pre-compression of Zr702 plate along rolling direction, while detwinning rather than secondary tensile twinning occurred when the pre-twinned sample was re-compressed along normal direction. Intermediate annealing between the pre-compression and the re-compression may hinder the subsequent detwinning. Moreover, the hindering effect was enhanced when larger pre-compression and longer annealing time were applied, which may be attributed to the annealing induced solute atoms precipitation and coherency loss of twinning boundary.

Surface finish effect on dry sliding wear behavior of thermally oxidized commercially pure zirconium

Abstract The effect of surface polishing on the wear behavior of thermally oxidized commercial pure zirconium (CP-Zr) under dry sliding conditions was investigated. Surface ground CP-Zr with a roughness of 0.21 μm (Ra) was thermally oxidized (TO) at 650 °C for 6 h. After TO, some samples were polished to smoothen the surface with a finish of 0.04 μm (Ra). The response of the polished and unpolished TO samples to dry sliding wear was investigated under unidirectional sliding conditions. The results show that surface polishing after TO affects the dry sliding wear behavior of TO CP-Zr in several aspects, including coefficient of friction, wear rate, crack formation and oxide layer breakdown. In particular, it is found that smoothening the TO surface favors the formation of semi-circular cracks in the wear track and accelerates oxide layer breakdown during dry sliding. A slightly rough TO surface helps to reduce the tendency of the oxide layer towards cracking and to increase the wear resistance at high contact loads. The mechanisms involved are discussed in terms of asperity contacts, crack formation, propagation and final fracture.

Fabrication and in vitro properties of zinc-based superhydrophilic bioceramic coatings on zirconium

In this study, as the first step, the bioceramic coatings were fabricated on Zr (commercial pure zirconium) in calcium acetate and β‑calcium glycerophosphate salt-based electrolyte by MAO (micro arc oxidation). And then, as the second step, the Zn (zinc) thin film layer measured an average thickness of 5 nm was coated on the MAO surface by TE (thermal evaporation). The phase composition, surface and cross sectional morphology, elemental composition and wettability of the MAO and Zn-based MAO coatings were analyzed by powder-XRD and TF-XRD, SEM, EDS-mapping and contact angle goniometer, respectively. The phases of cubic-ZrO2, perovskite-CaZrO3 and HA (hydroxyapatite) were observed on the surfaces by powder and TF-XRD analyses. The morphology of the MAO surface was not changed by TE although the chemistry of it was different from the MAO surface. The surfaces of both coatings were porous and rough. The Zn was uniformly deposited through the whole surface. After TE process, the wettability of the surface decreased and the Zn-based surface exhibited superhydrophilicity compared to MAO surface. In vitro bioactivity test of both coatings were investigated by immersion test in SBF (simulated body fluid) up to 10 days. The bone like apatite layer (secondary apatite) on the Zn-based bioceramic surface was compact and uniform compared the one on the MAO surface although it was completely propagated through both surfaces. In vitro anti-bacterial test of both coatings were carried out by microbial adhesion for Gram positive and Gram negative bacteria. It was observed that the microbial adhesions of the Zn-based bioceramic surfaces were lower than ones of the MAO bioceramic surfaces for all Gram-positive and Gram-negative bacteria.

On the state of deformation in a polycrystalline material in three-dimension: Elastic strains, lattice rotations, and deformation mechanisms

The deformation of polycrystalline zirconium is analysed at the individual grain level using three-dimensional Synchrotron X-ray Diffraction (3D-XRD) in combination with a Crystal Plasticity Finite Element (CPFE) model. The effects of elastic strains and lattice rotations on the shape and position of diffracted peaks are studied in detail. For this purpose, the three dimensional measured microstructure of a commercially pure zirconium (CPZr) sample was imported into a crystal plasticity finite element (CPFE) model to simulate the deformation of measured grains. The calculated lattice rotations and strains of the selected most active grains were subsequently used to forward simulate diffracted peaks. The simulated peaks are then compared to the 3D-XRD measured ones. It is shown that although the sample was deformed to 1.2% strain, soft grains exhibit significant peak smearing. Peak broadening is mostly affected by the deformation induced lattice rotation and less affected by the elastic strains. Further, the comparison of CPFE modelling and 3D-XRD results confirms that prism and basal slip are the most active systems and pyramidal <c+a> is present but only slightly active. A method is developed to determine the activity of possible slip systems. As an example, by comparing the simulated and measured peak positions as well as the rotations of the most affected diffraction peaks, it is shown that pyramidal <a> slip system is not active significantly at room temperature.

Characterization and in vitro properties of anti-bacterial Ag-based bioceramic coatings formed on zirconium by micro arc oxidation and thermal evaporation

In this study, at the first step, the commercial pure zirconium (Zr) was coated by micro arc oxidation (MAO) technique in solution, consisting of calcium acetate and β-calcium glycerophosphate salt. Then, silver (Ag) thin film layer that had an average thickness of 20nm was deposited on the MAO coated bioceramic surface by thermal evaporation (TE) technique. The phase structure, surface morphology, elemental composition and wettability of both Ag-coated and uncoated MAO coatings were characterized by powder-XRD and TF-XRD, SEM, EDX-mapping and contact angle goniometer, respectively. The powder and TF-XRD results indicated that cubic-zirconia, calcium zirconate and hydroxyapatite were detected on the surface after MAO and MAO+TE processes. Both coating surfaces were rough and porous. After TE process, Ag was homogeneously distributed on the surface. The Ag-based coated surface was hydrophobic compared to MAO surface. In vitro properties such as bioactivity and anti-bacterial tests of both coatings were investigated by soaking test in simulated body fluid (SBF) and bacterial formation, respectively. The apatite-forming abilities of both coatings were evaluated after soaking in SBF up to 10days. After soaking process, secondary apatite layer formed on the Ag-based MAO coatings was more homogenous and denser than one on the MAO surface, whereas secondary apatite structure was completely formed on both surfaces. Therefore, the bioactivity of the Ag-based MAO surfaces was significantly improved compared to the uncoated MAO coatings under SBF conditions. For 10 Gram-positive and Gram-negative bacteria, the bacterial adhesion of the Ag-based MAO coatings was considerably reduced compared to plain MAO surface.

Hydrogen Permeation in Nuclear Components at High Temperatures: Preliminary Electrochemistry Study

Adventitious hydrogen uptake into engineering materials frequently occurs as a consequence of the corrosion process at cathodic sites and tends to compromise, often severely, the mechanical properties of the alloy leading particularly to reduced fracture toughness and ductility and increased brittleness. In light water reactors (LWR) oxidation of the zirconium fuel cladding, and also other reactor internal components, results in pickup of hydrogen into the metal and limits how long the cladding can remain in the reactor environment, hence limiting the efficient consumption (“burn-up”) of the nuclear fuel. The fraction of hydrogen that is picked up by the metal in service, and the rate of the hydrogen diffusion, are key factors in understanding this phenomenon. It is thus of considerable interest to have a better understanding of the kinetics of hydrogen entry and diffusion/permeation in reactor pressure vessel materials (i.e. austenitic stainless steels and nickel based alloys) and particularly fuel cladding (zirconium alloys) under realistic operating conditions. The main purpose of this research is to adapt the well-known Devanathan-Stachurski permeation cell, to measure hydrogen diffusion at temperatures in the range 100-300°C, Figure 1. The work is divided in two stages. Firstly, an electrochemical study and selection of the candidate electrolytes, reference (RE) and counter (CE) electrodes for the oxidation and reduction compartments of the cell, within the temperature range specified above has been carried out. Secondly, hydrogen permeation measurements will be carried out in order to measure the entry kinetics and diffusion coefficient of hydrogen in reactor materials. This current report is focused on the first phase of the work. To realise the Devanathan-Stachurski concept at higher temperatures requires the use of concentrated salt solutions, molten salts or ionic liquids. For this work two molten salt eutectic mixtures were selected: NaOH + KOH (49:51 by mass; alkaline system) and NaHSO4 + KHSO4 (47:53 by mass; acidic system). Both electrolytes rely on residual dissolved water to supply protons and, hence, a humidified argon gas flow was provided with which the electrolyte was equilibrated. Platinum was used as the counter electrode while silver was found to behave as a sufficiently stable pseudo-reference electrode under the experimental conditions. Preliminary polarization curves (Figures 2 and 3) using both molten salts are shown within the working temperature range for Zr (99.2% – i.e. commercial purity zirconium), Zr4 (Zr + 1.5% Sn, 0.3% Fe+Cr and 0.2% Fe – i.e. zircalloy 4) and 316SS (16-18%Cr, 10-14% Ni, 2-2.5% Ni – i.e. AISI 316 austenitic stainless steel). The results demonstrate cathodic kinetics consistent with hydrogen evolution and anodic kinetics consistent with passivation in both electrolytes. Although 316SS is consistently less stable (i.e. corrodes more) under anodic polarisation. The bisulphate eutectic provides better hydrogen evolution kinetics but was found to be unstable above about 250°C and so the sodium/potassium hydroxide was selected as the electrolyte of choice. Conventionally, Devanathan-Stachurski cells operate under steady state (Fick’s 1stLaw) where the hydrogen activity is fixed on opposite sides of the permeation membrane. However in order to maximise the opportunity for detection of hydrogen given the extremely low diffusivity in zirconium, a protocol was adopted whereby the working electrode surface was first polarised into the cathodic region to evolve hydrogen then the potential was stepped into the anodic region to oxidise hydrogen. This concept is shown in figure 4. Figure 5 shows the results of two anodic polarisation in NaOH-KOH at 250°C from which it is clear that pre-polarisation into the cathodic region to evolve hydrogen results in a higher current that can be ascribed to the presence of hydrogen in the metal. Figure 1

A comparative study of the mechanical behaviour of thermally oxidised commercially pure titanium and zirconium

The objective of this study is to compare the mechanical behaviour of thermally oxidised commercially pure titanium (CP-Ti) and commercially pure zirconium (CP-Zr). For this purpose, these two bio-metals were thermally oxidised under the same condition (650°C for 6h) and the oxidised specimens were characterised using various analytical and experimental techniques, including oxygen uptake analysis, layer thickness and hardness measurements, scratch tests, dry sliding friction and wear tests and tribocorrosion tests in Ringer's solution. The results show that under the present thermal oxidation condition, 4 times more oxygen is introduced into CP-Zr than into CP-Ti and the oxide layer produced on CP-Zr is nearly 6 times thicker than that on CP-Ti. Thermally oxidised CP-Zr possesses a higher hardness, a deeper hardening depth and better scratch resistance than thermally oxidised CP-Ti. Under dry sliding and tribocorrosion conditions, thermally oxidised CP-Zr also possesses much better resistance to material removal and a higher load bearing capacity than thermally oxidised CP-Ti. Thus, thermally oxidised Zr possesses much better mechanical behaviour than thermally oxidised Ti.

Grain refinement and phase transition of commercial pure zirconium processed by cold rolling

The grain refinement process and phase transition phenomena of a cold-rolled zirconium have been systematically investigated. The grain refinement was accomplished via a sequential series of dislocation behaviors, reaching a final grain size of <100nm. The refinement process can be described as: (1) dislocation nucleation, multiplication and tangling inside the original coarse-grains, (2) formation of microbands via dislocation rearrangement, (3) further division of microbands into thin laths, (4) split of microbands and thin laths into subgrains and then nanograins. Two different types of HCP-FCC phase transitions were also discovered during the cold rolling process, with the transition mechanisms and their influences on the mechanical properties being discussed.

Effect of oxidation time on the tribological behavior of thermally oxidized commercially pure zirconium under dry sliding conditions

Thermal oxidation is an effective surface engineering technique to harden the surfaces of zirconium (Zr) and its alloys for improvement in friction and wear performance. In the present investigation, commercially pure zirconium (CP-Zr) is oxidized at 650°C for a wide range of times from 1h to 72h with the aim to study the effect of oxidation time on the tribological performance of CP-Zr. It is found that a dense, pore-free and adherent zirconium dioxide (ZrO2) layer can be produced at the surface for oxidation times less than 12h. Further increasing oxidation time leads to the gradual development of pores in the inner part of the oxide layer and oxidation breakaway characterized by accelerated oxidation kinetics and crack formation. Oxidation time has a significant effect on the tribological behavior of thermally oxidized CP-Zr under dry sliding conditions. The 6μm thick oxide layer produced by 6h treatment possesses the lowest friction, best wear resistance and the highest load bearing capacity. On the other hand, the thicker oxide layers produced by longer treatment times show deteriorated tribological behavior. The results are discussed in terms of the morphology of the oxide layer and crack propagation in the oxide layer and the underlying diffusion zone.

Study on Deformation Structure and Texture of Pure Zirconium with Large Grain Size Rolled at Liquid Nitrogen Temperature

Abstract The microstructure and the twinning behavior of the commercial pure zirconium with large grain sizes rolled uniformly at 77 K were studied. The deformation structures and the textures of samples with different rolling reductions were investigated by optical microscopy, scanning electron microscopy, electron backscattering diffraction (EBSD) and X-ray diffractometer. The EBSD results show that three types of twins, including C1{112}>11 10 11 11

The influence of grain size on acoustic emission characteristic in commercial-purity zirconium during tensile deformation

The influence of grain size on acoustic emission (AE) behavior during tension test in commercial-purity zirconium was investigated under a constant nominal strain rate at room temperature. Two deformation modes, dislocation slip and mechanical twinning, were found to be the physical sources for AE. The statistical analysis from metallographs showed that the quantity of mechanical twin gradually increased as grain size and tension strain increase. With grain size increased, the activity and intensity of the AE signals increased. The frequency distribution of the AE waveforms showed that two kinds of AE source were active with distinct frequency components during tension. By means of AE signal classification, the characteristic of AE due to dislocation slip and deformation twin were discussed respectively. The results showed that although dislocation was the dominant deformation mode, the primary AE source changed from dislocation to twin with the grain size increase. The AE activity due to twin was consistent with the metallographic evidence relating to the tensile deformation process.

Influence of grain size on fatigue crack propagation and acoustic emission features in commercial-purity zirconium

The influence of grain size on fatigue and corresponding acoustic emission (AE) features in commercial-purity zirconium were investigated. Fatigue crack propagation tests were conducted at room temperature with AE monitored simultaneously. The fatigue properties and AE sources were discussed combined with the microstructural and fractographic observations. The results showed that the increased grain size affected the fatigue crack stable propagation rate slightly, but it resulted in a significant increase of the AE counts rate. During the crack stable propagation, for the specimens with small-sized grains and medium-sized grains, the relationships between AE counts rate and fatigue stress intensity factor range were both generally according with the Pairs law, except some local fluctuations due to the regional occurrence of deformation twins. Especially, for the specimen with large grains, higher AE counts rate presented persistently, which were caused by twins appearing continuously at the edge of the crack. These results suggest that as the grain size increased in commercial-purity zirconium, twin became more frequent and made a more important contribution to the fatigue process, and the AE technique was sensitive to the crack propagation and the twin incidents during fatigue crack growth.

Effects of deep cryogenic treatment on the microstructure and mechanical properties of commercial pure zirconium

The effects of deep cryogenic treatment (DCT) on the microstructure and mechanical properties of commercial pure zirconium were investigated. Experimental results indicated that DCT induced a change in grain orientation and improved internal stress, which in turn increased dislocation density that led to improved hardness. Hardness in basal planes was found to be significantly larger than that in prism planes. Moreover, strength was enhanced in DCT-treated zirconium and the ductility was comparable to that of as-annealed zirconium. This phenomenon was due to the increase in dislocation density and the good ductility resulting from the motion of pre-existing dislocations and specific dislocation configurations. DCT led to the transformation of tensile fracture mode from mixed-rupture characteristics of quasi-cleavage and dimples to quasi-cleavage, thereby increasing compatible deformation capabilities. The possible mechanisms underlying microstructural modification, tensile strength, and hardness improvement were discussed.

Dynamic Recrystallization in Zirconium Alloys

Abstract In this investigation, the characteristics of dynamic recrystallization (DRX) in five Zr-alloys, namely, commercial pure zirconium (CP-Zr), Zircaloy-2 (Zr–Sn), Zr-2.5Nb (Zr–Nb), Zr-2.5Nb-0.5Cu (Zr–Nb-Cu), and Zr-1Nb-1Sn-0.1Fe (Zr–Nb–Sn–Fe), have been examined. For this purpose, processing maps were constructed using strain rate sensitivity (m) data as a function of temperature and strain rate. This has been done using compression tests carried out at constant true strain rate. The processing maps revealed the bounds of DRX domain as iso-contour of m in strain rate–temperature plane. Optical microscopy and transmission electron microscopy (TEM) were used to analyze the evolution of the microstructure and to ascertain the nature of dislocation mechanisms in deformed and quenched samples from the DRX domain. For all the alloys studied, TEM revealed complete modification of β-transformed microstructure to an equiaxed morphology containing dislocation substructure within. The variation of grain size with strain rate and temperature, high ductility, and a linear variation of log(grain size) with log(Z) (where Z is the Zener–Hollomon parameter) are some important characteristic features associated with DRX domains of Zr-alloys. While Nb exhibited strong influence on lowering the strain rate for the occurrence of DRX of CP-Zr, Sn addition (Zr–Sn) did not alter DRX characteristics. TEM observations neither revealed the nature of nucleation event nor identified the dislocation mechanism involved in the DRX process. In order to ascertain the rate controlling dislocation mechanism, the flow stress data were analyzed using a model of thermally activated flow. On the basis of the magnitudes of activation energy and apparent activation area, the cross-slip of screw dislocation has been identified as the rate controlling mechanism involved in the DRX process. The activation energy has been found to increase by alloying elements, which is expected to lower stacking fault energy (SFE) and increase separation between the partials. Further analysis of the data using Friedel’s model revealed that the activation energy for the cross-slip process can be decomposed into two parts—one related to the process of forming a constriction in the dissociated dislocations and the other needed for recombining the dissociated dislocations. While the former component (related to SFE) is dominant in Nb containing Zr-alloys, both the components are involved in controlling the deformation behavior of CP-Zr and Zr–Sn alloys. The effects of alloying elements on DRX characteristics and on the evolution of dislocation structure have been rationalized on the basis of cross-slip as the rate controlling dislocation mechanism in a qualitative manner. The importance of dynamic recovery in DRX process has been emphasized in view of this.

Development of nano-structure Cu–Zr alloys by the mechanical alloying process

Cu–Zr alloys have many applications in electrical and welding industries for their high strength and high electrical and thermal conductivities. These alloys are among age-hardenable alloys with capability of having nano-structure with high solute contents obtainable by the mechanical alloying process. In the present work, Cu–Zr alloys have been developed by the mechanical alloying process. Pure copper powders with different amounts of 1, 3 and 6 wt% of commercial pure zirconium powders were mixed. The powder mixtures were milled in a planetary ball mill for different milling times of 4, 12, 48 and 96 h. Ball mill velocity was 250 rpm and ball to powder weight ratio was 10:1. Ethanol was used as process control agent (PCA). The milling atmosphere was protected by argon gas to prevent the oxidation of powders. The milled powders were analysed by XRD technique and were also investigated by SEM observations. Lattice parameters, crystal sizes and internal strains were calculated using XRD data and Williamson–Hall equation. Results showed that the lattice parameter of copper increased with increasing milling time. The microstructure of milled powder particles became finer at longer milling time towards nano-scale structure. SEM observations showed that powder particles took plate-like shapes. Their average size increased initially and reached a maximum value then it decreased at longer milling times. Different zirconium contents had interesting effects on the behavior of powder mixtures during milling.