Zr Sn Research Articles

Effects of Zn content on microstructures and mechanical properties of Mg–Zn–RE–Sn–Zr–Ca alloys

The effects of Zn content on microstructures and mechanical properties of Mg–Zn–RE alloys have been investigated. The results indicate that RE-rich phases will change from the MgY and Mg12Nd binary phases in turn to Z (Mg12ZnRE), Z+W (Mg3Zn3RE2), W and W+I (Mg3Zn6RE) ternary phases as the Zn content increases from 0% to 4%. The grain size decreases when the Zn content increases from 0% to 2% and then increases, which is attributed to the variation of growth restriction factor resulted from the phase changes. The hardness continuously increases due to the formation of the ternary phases and their amount increase. The UTS and elongation first increase as the Zn content increases within the range of 0–2% and then decrease. The W phase is an ideal strengthening phase because the grain bonding strength of the unique W phase-containing alloy is higher than that of the Z or Z+W phase-containing alloy. Shrinkage porosities are easy to generate and the ternary phases distribute more and more continuously due to their amount increase when the Zn content exceeds 2%. The fracture regime changes from intergranular mode to transgranular mode as the Zn content increases from 0% to 2%, and then turns into transgranular mode again.

Tensile behavior at 700 °C in Ti–Al–Sn–Zr–Mo–Nb–W–Si alloy with a bi-modal microstructure

The effect of lamellar α phase (αL) thickness on tensile behavior at 700°C of BTi-6431S titanium alloy is investigated. Two types of bi-modal microstructures are introduced through different heat treatments. Both of them have similar volume fraction of equiaxed α phases (αe). One has thick α lamella named BTL, and another has fine α lamella named BFL. The results show that dynamic recrystallization (DRX) happens in the α phase during tensile process at 700°C. After being deformed at 700°C, the shape of αL in BFL and BTL transforms into sphere. BFL possesses higher tensile strength, and the elongation is twice as large as BTL at 700°C. Compared to the thick αL, the fine αL has more excellent accommodative deformation capability. There are cracks found to be of wedge type located at the grain triple junctions in both BFL and BTL. In addition, some small voids stay at the lamellar boundaries in BTL. In order to acquire a good combination of tensile strength and elongation at 700°C for BTi-6431S alloy, the thickness of αL should be reduced.

Strength and fatigue fracture behavior of Al–Zn–Mg–Cu–Zr(–Sn) alloys

The strength and fatigue fracture behavior of Al–Zn–Mg–Cu–Zr(–Sn) alloys were studied by performing tensile tests and fatigue crack propagation (FCP) tests. The microstructures of the experimental alloys were further analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM); phase analysis of these alloys was conducted with an X-ray diffraction (XRD). The results show that when Sn is included, growth of the recrystallization grains in the solution-treated Al–Zn–Mg–Cu–Zr alloy is obstructed, the precipitation-free zone (PFZ) of the overaged Al–Zn–Mg–Cu–Zr–Sn alloy becomes narrow, and the grain boundary precipitates are smaller. Consequently, the FCP resistance is higher. In addition, the overaged Sn-containing alloy has considerably higher tensile strength than the alloy without Sn.

The effect of Sn on autoclave corrosion performance and corrosion mechanisms in Zr–Sn–Nb alloys

The desire to improve the corrosion resistance of Zr cladding material for high burn-up has resulted in a general trend among fuel manufacturers to develop alloys with reduced levels of Sn. While commonly accepted, the reason for the improved corrosion performance observed for low-tin zirconium alloys in high-temperature aqueous environments remains unclear. High-energy synchrotron X-ray diffraction was used to characterize the oxides formed by autoclave exposure on Zr–Sn–Nb alloys with tin concentration ranging from 0.01 to 0.92wt.%. The alloys studied included the commercial alloy ZIRLO® (ZIRLO® is a registered trademark of Westinghouse Electric Company LLC in the USA and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited.) and two variants of ZIRLO with significantly lower tin levels, referred to here as A-0.6Sn and A-0.0Sn. The nature of the oxide grown on tube samples from each alloy was investigated via cross-sectional scanning electron microscopy. Atom probe analysis of ZIRLO demonstrated that the tin present in the alloy passes into the oxide as it forms, with no significant difference in the Sn/Zr ratio between the two. Synchrotron X-ray diffraction measurements on the oxides formed on each alloy revealed that the monoclinic and tetragonal oxide phases display highly compressive in-plane residual stresses with the magnitudes dependent on the phase and alloy. The amount of tetragonal phase present and, more importantly, the level of tetragonal-to-monoclinic phase transformation both decrease with decreasing tin levels, suggesting that tin is a tetragonal oxide phase stabilizing element. It is proposed that in Zr–Nb–Sn alloys with low Sn, the tetragonal phase is mainly stabilized by very small grain size and therefore remains stable throughout the corrosion process. In contrast, alloys with higher tin levels can in addition grow larger, stress stabilized, tetragonal grains that become unstable as the corrosion front continues to grow further inwards and stresses in the existing oxide relax.

The effect of alloying on the ordering processes in near-alpha titanium alloys

The substructure of near-alpha Ti–Al–Sn–Zr–Mo–Si alloys containing up to 12.5at% aluminum was studied by transmission electron microscopy (TEM). It was shown that long-range order sections are formed at aging temperatures up to 500°C in alloys, high in aluminum, and the ordered phase is formed by the nucleation and growth mechanism at 700°C aging temperatures. Causes of changing the phase transformation mechanism have been discussed, and the relationship between the structure and properties of alloys, depending on modes of heat treatment has been analyzed. Also the influence of aluminides and silicides precipitation on the mechanical alloy properties after aging was examined. It was shown that the aluminide formation led to a slight hardening and a significant viscosity decrease. The silicide particles formation reduced the heat resistance properties, due to the depletion of the solid solution by silicon.

Precipitation and growth study of intermetallics and their effect on oxidation behavior in Zr–Sn–Fe–Cr alloy

Microstructural evolution of the second phase precipitates and their microchemistry in Zr–Sn–Fe–Cr alloy during various alpha annealing heat treatments have been investigated by transmission electron microscopy and energy dispersive spectrometer attached with scanning transmission microscopy. Two types of precipitates, namely, Zr – rich Zr2(FeCr) with aspect ratio one and Zr lean Zr(FeCr)2 with parallelepiped morphology were identified. Size distribution of the precipitates was estimated from small angle neutron scattering. The effect of precipitate size, its distribution and matrix microstructure on the oxidation behavior of the alloy was studied during accelerated autoclaving. The shorter duration annealing at 700°C does not improve the oxidation resistance of the alloy as it would lead to formation of non uniform distribution of alloying elements and precipitates in the matrix. It is revealed that alpha annealing at 700°C for 10h imparts a significant resistance to oxidation as well as substantial formation of Zr(FeCr)2 precipitates.

Study of precipitate evolution and recrystallization of β-quenched Zr–Sn–Nb–Fe–Cr–Cu alloy during aging

Electron backscatter diffraction, electron channeling contrast, secondary electron imaging techniques and micro-hardness tests are jointly employed to investigate the precipitate evolution and recrystallization of a Zr–0.85Sn–0.4Nb–0.4Fe–0.1Cr–0.05Cu alloy during aging between 600 and 700°C following β-quenching treatment. Results show that the implemented quenching produces plate structures with specific orientations. For specimens aged at lower temperature or for shorter time, the plate structures maintain yet second phase particles (SPPs) precipitate along the plate boundaries. For specimens aged at higher temperature or for longer time, recrystallizations are completed. The recrystallized structure presents irregular grain shapes, non-uniform grain sizes and randomly distributed SPPs. In spite of the morphology discrepancies, some recrystallization grains inherit the orientation feature of the prior α plates. With increasing temperature and time, hardness decreases and no hardness peak is observed. Reasons accounting for the formation of different microstructural features are tentatively discussed.

Growth behavior study of second phase particles in a Zr–Sn–Nb–Fe–Cr–Cu alloy

The growth behavior of the second phase particles (SPPs) in a Zr–Sn–Nb–Fe–Cr–Cu alloy during aging (600–700°C, 30–1800min) has been investigated using scanning electron microscopy (SEM) and an image analysis technique. Microstructural observations show that the precipitated SPPs distribute linearly along the boundaries of α plates at the initial aging stage. As the aging time prolongs and/or temperature increases, the linear distribution feature of SPPs weakens gradually and finally a random distribution is formed. A numerical analysis confirms that the growth of SPPs follows well the second order kinetics of Kahlweit theory and the activation energy is experimentally determined to be 194kJ/mol. The reason for the larger growth activation energy of the SPPs in the experimental alloy, compared to that in Zircaloy-4, is discussed and ascribed to the addition of Nb element.

Nonlinear dielectric thin films for high-power electric storage with energy density comparable with electrochemical supercapacitors

Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb(0.97)La(0.02))(Zr(0.90)Sn(0.05)Ti(0.05))O(3) (PLZST) antiferroelectric ceramic thin films, Pb(Zn(1/3)Nb(2/3))O(3-)Pb(Mg(1/3)Nb(2/3))O(3-)PbTiO(3) (PZN-PMN-PT) relaxor ferroelectric ceramic thin films, and poly(vinylidene fluoride) (PVDF)-based polymer blend thin films. The results showed that these thin film materials are promising for electric storage with outstandingly high power density and fairly high energy density, comparable with electrochemical supercapacitors.

Catalytic reduction of SO 2 over Sn–Zr based catalysts for DSRP under high pressure

The catalytic activity of Sn–Zr based catalysts and the production behavior of COS during SO 2 reduction were investigated for the catalytic reduction of SO 2 under high pressure condition in this study. The SnO 2, ZrO 2 and SnO 2–ZrO 2 used as the catalysts were prepared by the precipitation and co-precipitation methods. The activity tests for the Sn–Zr based catalysts were carried out in the range of 200–450 °C at atmospheric pressure and 20 atm. CO was also used as the reducing agent for the reduction of SO 2. The catalytic activity and a surface area of the SnO 2–ZrO 2 prepared by the co-precipitation methods were higher than that of the SnO 2 and SnO 2–ZrO 2 catalysts prepared by the physical mixing. It was concluded that the surface area of SnO 2–ZrO 2 catalyst prepared by the co-precipitation increased due to the formation of the lattice defects. A high yield of elemental sulfur was also maintained for 50 h in the durability test. Carbonyl sulfide is produced by the reaction between CO and the elemental sulfur produced during the reduction of SO 2, and was also produced by the gas–solid reaction between the metal sulfide and CO. The selectivity of COS was high at the intermediate level of conversion of SO 2. Since the vapor pressure of elemental sulfur decreased with increasing pressure, the production of COS was reduced to a greater extent at the high SO 2 conversion observed at high pressure. From these results, it was confirmed that SnO 2–ZrO 2 is a suitable catalyst for the catalytic reduction of SO 2 at high pressure.

Role of ZrO2 incorporation in the suppression of negative bias illumination-induced instability in Zn–Sn–O thin film transistors

Thin film transistors (TFTs) with In and Ga-free multicomponent Zn–Sn–Zr–O (ZTZO) channel layers were fabricated using the cosputtering approach. The incorporation of ZrO2 into the Zn–Sn–O (ZTO) films increased the contact resistance, which led to the degradation of the transport properties. In contrast, the threshold voltage shift under negative bias illumination stress (NBIS) was largely improved from −12.5 V (ZTO device) to −4.2 V (ZTZO device). This improvement was attributed to the reduction in the oxygen vacancy defects in the ZTZO film, suggesting that the photoinduced transition from VO to VO2+ was responsible for the NBIS-induced instability.

Anomalous glass transition behavior in Cu–Zr–Sn alloy system

We discuss the effect of Sn addition on anomalous glass transition behavior in Cu–Zr bulk-forming metallic glasses. We found that an unusual endothermic reaction in Cu 55Zr 40Sn 5 ribbon can originate from the growth reaction of quenched-in nuclei from 0.4 nm to 3.7 nm in the supercooled liquid region. This anomalous devitrification may prove useful for the synthesis of a novel composite with uniform atomic/nanometer scale heterogeneity modulated by controlling cooling rate as well as by tailoring alloy composition.

Effect of Vacancy-Site Occupation in Half-Heusler Compound ZrNiSn on Phase Stability and Thermoelectric Properties

ABSTRACTThe half-Heusler compound ZrNiSn has a quite small solubility for Ni from the stoichiometric composition towards the Ni-rich direction since Ni atoms are not supposed to occupy the vacancy-site. Nevertheless, Co and Ir atoms preferably occupy the vacancy-site of ZrNiSn, which is contrary to the prediction that they would substitute for Ni sites. This implies that the phase stability of the compound gradually changes toward that of the Heusler compound Zr(Ni,M)2Sn (M = Co, Ir). It has been confirmed that there exists a two-phase field between half-Heusler Zr(Ni,Cox)Sn and Heusler Zr(Ni,Co)2Sn. The n-type thermoelectric property of ZrNiSn can be converted to p-type by the addition of Co and Ir within the compositional range of the half-Heusler phase. The occupation of vacancy sites by Co and Ir atoms leads to a drastic reduction in the thermal conductivity owing to the enhancement of phonon scattering. With further Co addition, the Heusler phase Zr(Ni,Co)2Sn alloys show metallic behavior.

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.

Threshold stress intensity factor for delayed hydride cracking of a recrystallized N18 alloy plate along the rolling direction

The objective of this study is to obtain the threshold stress intensity factor, K IH, for an initiation of delayed hydride cracking in a recrystallized N18 (Zr–Sn–Nb–Fe–Cr) alloy plate which was manufactured in China, gaseously charged with 60 ppm of hydrogen by weight. By using both the load increasing method and load drop method, the K IH’s along the rolling direction were investigated over a temperature range of 150–255 °C. The results showed that K IH along the rolling direction was found to be higher in the load increasing method than that in the load drop method. In the load increasing method, K IH’s of the N18 alloy plate appeared to be in the range of 31 – 32.5 MPa m , and K IH in the load drop method appeared to be in the range of 27.5 – 28.6 MPa m . This means that the N18 alloy plate has high tolerance for DHC initiation along the rolling direction. The texture of a N18 alloy plate was investigated using an X-ray diffraction and the K IH was discussed based on texture and analytically as a function of the tilting angle of hydride habit planes to the cracking plane.

An experimental study of the Fe–Sn–Zr ternary system at 900 °C

The partial isothermal section of the Fe–Sn–Zr system at 900 °C reported in Ref. [7] was completed. As compared with this section, three new ternary compounds were evidenced (Y, C36 and Fe6Sn6Zr), one compound previously reported with a homogeneity domain (X) was shown to consist in fact of two separate compounds with close compositions (X′ and X″). The crystal structure of the previously reported N phase was determined ab initio from powder diffraction data.

PREDICTION OF CRITICAL TEMPERATURE FOR DELAYED HYDRIDE CRACKING IN IRRADIATED N18 ZIRCONIUM ALLOY

Delayed hydride cracking (DHC) has been recognized as a potential threat to the structural integrity of zirconium alloy components in water–cooled nuclear reactors since the early 1970 s. Although DHC has been studied for a long time, most of the investigations were focused on unirradiated Zr–Nb and Zr–Sn alloys, no information was found on Zr–Sn–Nb alloy. Currently, several new Zr–based alloys have been developed from the point of view of enhancement of corrosion resistance and hydrogen pickup properties. In China, N18 (Zr–Sn–Nb) alloy has been developed based on Zr–Sn and Zr–Nb systems to meet the requirements of higher fuel burn–up. Therefore, it is necessary to investigate the DHC behavior of N18 alloy systematically. The objective of this study is to predict the critical temperatures for initiating and arresting DHC in irradiated N18 alloy. A model used to forecast DHC critical temperature of irradiated zirconium alloys was established based on the terminal solid solubility of hydrogen in irradiated zirconium alloys and stress–induced hydrogen diffusion. By using the model, the critical temperatures for irradiated N18 alloy were predicted. The result showed that the irradiated N18 alloy has high sensitivity for DHC initiation, because neutron irradiation increased the solubility of hydrogen and yield strength of N18 alloy. Compared with unirradiated N18 alloy, the critical temperature * $! AE# JJXM–QNJJ–09–04–04 % : 2009–12–29, &% : 2010–03–31 $%' : ! , !, 1981 , # , DOI: 10.3724/SP.J.1037.2009.00868

Improvement of glass-forming ability and phase separation in Cu–Ti-rich Cu–Ti–Zr–Ni–Si bulk metallic glasses

Present study reports improvement of glass-forming ability (GFA) and phase separation in Cu–Ti-rich Cu–Ti–Zr–Ni–Si bulk metallic glasses (BMGs) by tailoring the constituent elements. The MA of metalloid element, Sn having relatively large negative enthalpy of mixing can lead to improve GFA (up to 8 mm in diameter) as well as thermal stability (up to Δ T x = 48 K) by optimizing the substitution element. And the addition of elements having relatively large positive enthalpy of mixing (partial substitution of Zr or Ti with Y) can lead to the liquid state phase separation in Cu–Ti–Sn–Zr–Ni–Si BMG, although the addition lead to drastic deterioration of the GFA.

Cu-Sn-Zr-P Alloy for a High-Strength Heat-Exchanger Tube

In order to improve the mechanical properties of a Cu–Sn alloy at elevated temperatures as well as the heat-resistant properties of said alloy, the effects of adding a small amount of zirconium were investigated. It was clarified that the addition of zirconium increases the tensile strength and elongation properties after a high-temperature heat treatment, and the addition of more than 0.04% zirconium increases the tensile strength to approximately 300 MPa. For a seamless tube, the tensile strength of a Cu–0.65Sn–0.05Zr–0.008P (mass%) alloy was 301 MPa, with an elongation of 47%. Furthermore, it exhibited high heat-resistant properties after brazing. Thus, it is expected that the Cu–Sn–Zr–P alloy can be used to make seamless tubes for heat exchangers.

Corrosion resistance of titanium-containing dental orthodontic wires in fluoride-containing artificial saliva

This study was to investigate the corrosion resistance of different Ti-containing dental orthodontic wires (including Ni–Ti, Ni–Ti–Cu, Ti–Mo–Zr–Sn, and Ti–Nb alloys) in acidic fluoride-containing artificial saliva using cyclic potentiodynamic polarization curve measurements. Different NaF concentrations (0%, 0.2%, and 0.5%), simulating the fluoride contents in commercial toothpastes, were added to the artificial saliva. Surface characterization was analyzed using X-ray photoelectron spectrometry. Cyclic potentiodynamic polarization curves showed that the presence of fluoride ions, especially 0.5% NaF, was detrimental to the protective ability of the TiO 2-based film on the Ti-containing wires. This might lead to a decrease in the corrosion resistance of the tested alloys, i.e. an increase in the corrosion rate and anodic current density and a decrease in the passive film breakdown potential. Among the tested Ti-containing wires, the Ni–Ti and Ni–Ti–Cu wires containing mainly TiO 2 on surface film were more susceptible to fluoride-enhanced corrosion, while the Ti–Mo–Zr–Sn and Ti–Nb wires containing MoO 3/ZrO 2/SnO and Nb 2O 5, respectively, along with TiO 2 on surface film were pitting corrosion resistant and showed a lower susceptibility to fluoride-enhanced corrosion. The difference in corrosion resistance of the tested commercial Ti-containing dental orthodontic wires was significantly dependent on the passive film characteristics on wires’ surface.