Hydride formation in Zr-1.15 wt% Cr-0.1 wt% Fe during corrosion in water and steam

Abstract

The precipitation of zirconium hydride in an alloy of nominal composition Zr-1.15 wt%Cr-0.1 wt% Fe during corrosion in both 773K steam and 573K water has been studied using, primarily, thin-foil electron microscopy. In 773K steam a globular form of the f.c.c. δ-hydride is formed which has the following orientation relationship with the a-zirconium matrix.

(111)_δ//(101¯0)_α′[11¯0]_δ//[112¯0]_α

The hydride formed at 573K also has the δ-structure but forms as thick needles or plates. The morphology of the hydride is controlled at 773K by the need to reduce the surface area to a minimum. The hydride in all samples was evenly distributed. This is considered to be indicative of some form of supersaturation which is produced by thermal cycling.

Résumé

La precipitation d'hydrure de zirconium pendant la corrosion D'alliages de ce métal contenant des pourcentages en poids de 1.15% de Cr et 0.1% de Fe a été étudiée à l'aide du microscope électronique à feuille mince. Pour la corrosion qui se produit dans la vapeur à 773deg;K, une forme globulaire d'hydrure á faces cubiques centrées a été observée. Cet hydrure est orienté par rapport à la matrice d' α-zirconium:

(111)_δ//(101¯0)_α′[11¯0]_δ//[112¯0]_α

L'hydrure formé à 573°K a une structure δ, mais forme des aiguilles epaigses ou des plaques. La morphologie de l'hydrure est controlee a 773°K par le besoin de réduire la surface à un minimum. L'hydrure dans tous les spécimens était uniformément distribué. Ceci est considéré comme une indication d'une forme de supersaturation produite lors du cycle thermique.     

Hydride orientation and tensile properties of Zr-2.5 wt% Nb pressure tubing hydrided while internally pressurized

Abstract

An investigation was carried out to determine the orientation and the effect on tensile properties of hydrides precipitated in heat-treated Zr-2.5 wt% Nb tubing during the corrosion hydriding of internally pressurized samples. It was found that as the stress during hydriding was increased the hydrides gradually assumed a characteristic radial orientation nearly perpendicular to the hoop stress. The observed radial hydride orientation was influenced by prior β grain size, residual quenching stresses, cold-work strains and stresses applied while the pressure tube was being hydrided. Hoop stresses in excess of 20,000 psi were required to produce complete radial orientation of the hydrides.

Transverse tensile tests on the hydrided tubes were conducted using a reduced section ring technique. These tests revealed a low ductility at low temperatures with a transition in the range 60°–100°C for material with radially oriented hydrides. Low tensile ductility was observed at significantly higher temperatures when a massive hydride layer was present near the surface of the test samples.

Résumé

Dans des tubes en Zr-2.5 % poids Nb trempé et vieilli et soumis à la corrosion hydrogenante sous pression, une étude a été entreprise pour déterminer l'orientation des hydrures précipités et leurs effets sur les propriétés mecaniques en traction. Les résultants indiquent que lorsque la contrainte augmente pendant léhydrogenation, les hydrures acquièrent graduellement une orientation radiale caractéristique, à peu prés perpendiculaire à la contrainte circonférentielle. Cette orientation radiale des hydrures est influencée par la taille du grain β initial, les contraintes de trempe résiduelles, les déformations à froid et les contraintes appliquées lorsque le tube sous pression est hydrogéné. Des contraintes circonférentielles supérieures à 20,000 psi sont nécessaires pour produire une orientation parfaitement radiale des hydrures.

Des essais de traction en travers des tubes hydrogénés ont été réalisés en utilisant la technique de l'anneau à section réduite. Ces essais ont révélé une faible ductilité à basses températures avec une transition dans le domaine 60°–100°C pour le matériau à hydrures orientés radialement. Une faible ductilité en traction a été observée à des températures beaucoup plus hautes quand une couche massive d'hydrures existait près de la surface des échantillons.     

Metallurgical properties of heat-treated Zr-2.5 wt% Nb pressure tubes irradiated under power reactor conditions

Abstract

Three heat-treated pressure tubes of Zr-2.5 wt % Nb were irradiated as components of Chalk River reactor loops under conditions similar to those in Canadian power reactors of pressurized heavy water (CANDU-PHW) and boiling light water (CANDU-BLW) type. Two other tubes, one of which had been artificially hydrided to about 200 ppm H2, were irradiated unstressed in air at about 300°C.

Post-irradiation examination of the tubes shows that they can withstand severe through-wall defects: the critical crack length exceeds 43 mm at a hoop stress of 179 MN/m2 at 20° and 300°C. Mechanical strength was increased by neutron irradiation: eliminating autoclaving offers the advantage of lower rates of oxidation and hydrogen pickup.

Résumé

Trois tubes de force en alliage Zr-2.5 % pds Nb, ayant subi des traitements thermiques ont été irradiés comme composants de boucles dans le réacteur à Chalk River. Les conditions ressemblaient à celles dans les réacteurs canadiens à eau lourde sous pression (CANDU-PHW) et à eau légère bouillante (CANDU-BLW). Deux autres tubes, l'un ayant subi un traitement d'hydruration jusqu'à 200 ppm de H₂ ont été irradiés sans contrainte sous air à 300°C.

Les examens ultérieurs ont montré que les tubes peuvent supporter des défauts sévères qui traversent les parois: la longueur critique de fissure est supérieure à 43 mm pour une contrainte de 179 MN/m² a 20° et a 300°C. Une irradiation aux neutrons augmentent la résistance mécanique. Les taux d'oxydation et de dissolution d'hydrogène se voient diminuer si les tubes ne sont pas traités antérieurement à l'autoc1ave.     

Microstructure of welded and weld-simulated 3Cr-1.5Mo-0.1V ferritic steel

Ferritic steels are often used in thick-plate form. The feasibility of electron-beam welding such thick plates and the mechanical properties of these welds were examined in a recent study. In this investigation, the microstructures of these thick-plate, electron-beam welds were evaluated. The study was carried out on a 3Cr-1.5Mo-0.1V steel. Weld simulations were used to aid in the study of the heat-affected zone (HAZ) microstructure. Such simulations allowed for a more reliable and detailed evaluation of the variation in microstructure with distance from the fusion line. The structures were related to microhardness measurements made across the width of the weld and the HAZ. The fusion zone and the immediately adjacent HAZ consisted of bainite platelets with narrow films of retained austenite at many of the bainite platelet boundaries. Farther away from the fusion zone, the structure was a two-phase mixture of bainitic platelets and ferrite produced by heating base metal between theAc ₁ and theAc ₃ temperatures. Still farther from the weld, the structure consisted of tempered bainite, with the degree of tempering decreasing with distance from the fusion line. The bainite plus ferrite region and the tempered bainite section are associated with a soft zone in the hardness profile across the weld. A postweld heat treatment (PWHT) was found to reduce the hardnesses of the fusion zone, HAZ, and base material to relatively uniform levels. The structure across the weld and HAZ after a PWHT is tempered bainite except in one section of the HAZ in which tempered bainite and ferrite coexist.     

Development of texture and structure in Zr-2.5 wt% Nb extruded tubes

Abstract

Factors which affect the texture and microstructure of Zr-2.5 wt % Nb extruded tubes have been investigated. The major factor that determines th~ texture is the way the metal flows, which is controlled by the die shape, the extrusion ratio and the lubricant. The microstructure is controlled by the temperature during extrusion and the cooling rate afterwards.

Résumé

Les auteurs ont examiné les facteurs influençant la texture et la microstructure de tubes de Zr-2.5 % Nb filés à la presse. La texture surtout fixée par l'écoulement du métal; cet écoulement est contrôle par la forme de la filière, le rapport de filage et le lubrifiant. La température de filage et le taux de refroidissement subséquent flxant la microstructure.     

Fe-1.5C-1.5Cr-1.5Al超高碳钢碳化物的球化和力学性能

对Fe-1.5C-1.5Cr-1.5Al超高碳钢碳化物的球化工艺及力学性能进行了研究.扫描电镜观察表明,加入铝,可抑制锻后空冷条件下先共析网状碳化物的析出;利用铝合金化作用和成分不均匀化奥氏体加热控制,提出了2种无形变球化处理工艺:①离异共析等温球化;②预冷淬火 高温回火.2种球化处理工艺均能获得良好的球化组织和良好的综合力学性能:Rm≥1 000 MPa,Re≥700 MPa,A10=10%～14%.拉伸断口具有明显的缩颈,断口形貌呈具有典型的韧窝特征.     

Ti-44Al-5V-1Cr-0.3Ni-0.1Hf-0.15Gd合金的微观组织和拉伸性能

针对变形量达86%的锻造Ti-44Al-5V-1Cr-0.3Ni-0.1Hf-0.15Gd(原子分数,%)合金,对其进行热处理获得近层片组织,研究变形合金及其近层片组织的微观组织特征,并进行了室温、700℃和800℃拉伸实验.组织观察发现,近层片组织由层片团、分布于层片团界的β相以及弥散分布于基体的椭圆状Gd析出物组成.层片团的平均尺寸为40μm,层片组织、β相和Gd析出物的体积分数分别为93.73%、5.25%和1.02%.拉伸结果显示,室温下合金试样的平均抗拉强度为865MPa,平均延伸率可达4.17%,700℃时其平均抗拉强度和延伸率分别为643MPa和22%.Ti-44Al-5V-1Cr-0.3Ni-0.1Hf-0.15Gd合金不仅具有与高β相TiAl合金相当的塑性变形能力,且室温塑性也得到显著提高,这主要归因于β相体积分数的下降和Gd化合物对微观组织室温塑性的贡献.     

Microstructure and mechanical properties of a 3Cr-1.5Mo steel

Tensile and impact properties were determined for a steel (3 wt pct Cr-1.5 wt pct Mo-0.1 wt pct V-0.1 wt pct C) considered a candidate for elevated-temperature pressure-vessel applications. The steel was tested in two heat-treated conditions: normalized and tempered and quenched and tempered for various tempering conditions. Similar tempering treatments for the quenched and the normalized steels led to similar strengths. However, for the lowest tempering parameter used, the impact properties for the quenched-and-tempered steel exceeded those for the normalized-and-tempered steel, resulting in an excellent ductile-brittle transition temperature (-70 °C) and upper-shelf energy (225 J) for the quenched-and-tempered steel at a high strength (770 MPa ultimate tensile strength). Further tempering reduced the strength for the steel in both heat-treated conditions. The impact properties of the quenched steel were only slightly changed by further tempering, but those for the normalized steel improved, eventually equaling those for the quenched-and-tempered steel. The difference in impact properties after the two heat treatments was attributed to a difference in bainite microstructures.     

Effect of AB2-based alloy addition on structure and electrochemical properties of La0.5Pr0.2Zr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2 hydrogen storage alloy

The La 0.5Pr0.2Zr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2(M1) and Zr0.65Ti0.35(Mn0.2V0.2Cr0.15Ni0.45) 1.76(M2) hydrogen storage alloys were prepared by inductive melting.In addition,the M1+30 wt.%M2 composites were successively prepared by using high-energy ball milling technology.From the X-ray diffraction(XRD) analysis,it was found that M1 and M2 alloys still retained their respective main phases in the M1+30 wt.%M2 composites.The scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) indicated that the decrease in discharge capacity of M1 and M2 alloy electrodes was ascribed to the oxidation-dissolution of La,Pr,Mg and Ti,Mn,V,Cr active elements,respectively.The electrochemical studies showed that the M1+30 wt.%M 2 composite electrode ball milling for 5 min exhibited excellence cyclic stability(92.3%) after 80 charge/discharge cycles,which was higher than 77.7 % and 85.6% of M1 and M2 alloy electrodes,respectively.Moreover,at the discharge current density of 1200 mA/g,the high rate discharge ability(HRD) of the M1+30 wt.%M2 composite electrode increased from 61.5%(5 min) to 70.3%(10 min).According to the linear polarization,Tafel polarization and cyclic voltammograms(CV),the electrochemical kinetics of hydrogen reaction on the surface of the electrode and hydrogen diffusion rate in the bulk of alloy were also improved in the M1+30 wt.%M2 composite with increasing ball milling time.     

医用Zn-1.5Mg合金的组织与性能研究

研究了医用Zn-1.5Mg合金的微观组织变化,探讨了其对力学性能的影响.对铸态、均匀化处理和轧制态Zn-1.5Mg合金的微观组织进行了表征,分析了合金的相组成.选取变形量为49%和73%的轧制态Zn-1.5Mg合金,在模拟体液中分别浸泡1、2、4、8、14、22、32天,统计了腐蚀速率的变化.结果表明:铸态Zn-1.5Mg合金的相组成主要为η-Zn相、Mg_2Zn_(11)相和MgZn_2相,均匀化处理后MgZn_2相消失.铸态Zn-1.5Mg合金均匀化后共晶组织的片层状形貌消失,显微组织变得更加均匀.经总压下量73%轧制变形后,枝晶细化.轧制后的浸泡实验显示,样品浸泡4天后腐蚀速率基本保持在0.2 mm/a左右,电化学实验显示两种轧态试样腐蚀电压在-0.9 V左右.     

Mechanical and microstructural properties of alloy 800

The evolution of microstructural and mechanical properties of alloy 800 with respect to operating conditions of the steam generator tubings of fast breeder reactors have been analyzed and presented. On the microstructural side two phenomena have important influence on the mechanical properties, namely γ′ and carbide precipitation. Gamma prime precipitation occurs in alloy compositions containing ≳0.50 pct Ti + Al, inducing mechanical property changes and, in particular, improving the long term creep resistance. Its growth rate follows the exponential law which, when extrapolated, yields an overaging time beyond 4 × 10⁴ h at ≲550°C. M₂₃C₆ carbide precipitation starts in early stages of exposure at 500 to 600°C, being of heterogeneous nature and forming mainly on the grain boundaries. The M₂₃C₆ carbides advance perpendicular to the surface of one of the austenite grains, commonly having a <110>_γ//<110>M₂₃C₈relationship, and occasionally develop into well defined cellular precipitates. On the mechanical side, a sharp creep ductility decline is observed when either, or in particular both, strong γ′ strengthening and discontinuous precipitation develop in the matrix. It is argued that this decline is principally due to the latter phenomenon and is accentuaged by matrix strengthening. Formerly Associate Professor, Metallurgical Engineering Department, Arya Mehr University of Technology, Tehran, Iran.     

Effects of adding different types of carbon on the structure and magnetic properties of SmCo6.9Hf0.1 alloy

In this paper,SmCo6.9 Hf0.1 as-cast alloys and ribbons with the addition of either graphite（C） or carbon nanotubes（CNTs） were prepared by arc melting and melt-spinning,respectively.The effects of adding carbon on the structure and magnetic properties SmCo6.9 Hf0.1 were investigated by means of X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,magnetic force microscopy（MFM） and vibrating sample magnetometer（VSM）.It was found that the microstructure and magnetic structure of SmCo6.9 Hf0.1 ribbons were changed obviously due to the introduction of C or CNTs,although their crystal structure was characterized as the same Sm（Co,Hf）7 single phase,no matter carbon was added or not.As a result,the magnetic properties of carbon-contained ribbons were enhanced in a certain degree.This was considered to be related to the refined equiaxed grains,small domain size and the pinning effect of C or CNTs-rich regions.The magnetic properties of SmCo6.9 Hf0.1（CNTs）0.05 ribbons reached Hc =12.5 kOe,Mr =57.0 emu/g and Mr/M2 T =0.788.     

The magneto-elastic properties of the invar alloy,Fe3Pt

The variations of the lattice parameter, the Curie temperature (determined from specific heat measurements), and the temperature variation of the elastic constants C, C′, and C_l in an applied magnetic field of 0.8 T have all been measured as a function of the long-range order in a single crystal of iron-platinum alloy with very nearly the stoichiometric composition Fe₃Pt. It is found that the Invar effect in partially ordered Fe-25 Pt is larger than in other Fe-Pt alloys or in well-known Invar alloys such as Fe-35 Ni. The results for Fe-25 Pt are analyzed and interpreted in terms of a model of nearest-neighbor exchange interaction which takes account of the spatial variation of the average exchange integral. The best fit with the experimental data is obtained by assuming an average spin of unity. Using ordering as the controlled variable avoids the difficulties inherent in studies which have relied on a compositional variable. The model satisfactorily describes the magnetic contribution to the elastic constants and the variation of Curie temperature with changes in the long-range order. It is concluded that Fe-Pt coupling is ferromagnetic and Fe-Fe coupling antiferromagnetic.     

In-Plane structure and properties of Fe multilayers

The structural properties of Fe multilayers are being studied by three techniques—standard reflection X-ray diffraction, transmission electron diffraction (TED), and extended X-ray absorption fine structure (EXAFS). The patterns of structural behavior are presently for two prototypical systems: Fe/Si, which is a simple multilayer, and Fe/V, which is a superlattice. Structural data for the Fe/Si system are complemented with results of a Mossbauer study. This invited paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Mechanical properties and microstructure of centrifugally cast alloy 718

The relationship between the microstructure and mechanical properties of alloy 718 was investigated for two discs centrifugally cast at 50 and 200 rpm and given a duplex age heat treatment. The results of mechanical property tests at temperatures from 426 to 649 °C showed that the tensile yield and ultimate strength levels of both castings were similar. However, the creep-rupture properties were considerably enhanced for the casting produced at 200 rpm. Comparison of the radial and transverse creep properties of each disc indicated that creep life was generally independent of orientation, but ductility was greatest for specimens oriented transverse to the radial direction of the casting. Fatigue crack propagation performance was not greatly influenced by orientation or mold speed parameters and was comparable to wrought alloy 718 when compared on the basis of stress intensity factor range. The centrifugal casting process was found to produce a homogeneous microstructure free of porosity but with the expected segregation of solute alloying elements to Laves and carbide phases. The effect of the as-cast microstructure on the mechanical behavior and the potential influence of hot isostatic pressing to improve the microstructure are discussed.     

Mechanical properties of internally nitrided Fe−Ti and Fe−Cb alloys

Highly formable ferrous alloys containing Ti or Cb can be strengthened by a nitrogenation treatment which produces alloys containing dispersions of submicroscopic particles of TiN or CbN. By this treatment, the yield strength of alloys containing only 0.2 pct Ti or 0.3 pct Cb is increased from 105 to 700 MPa while retaining tensile elongations of 10 to 15 pct, good bendability, and good impact resistance. The CbN particles begin to coarsen at 600°C causing softening, a decrease in electrical resistivity, and an increase in impact resistance. The first response to annealing of the Fe−TiN system is a drop in resistivity which also begins at 600°C. Attending this change is an increase in hardness which continues to 800°C where the first precipitates become discernible by transmission electron microscopy. Subsequently, hardness falls as the particles grow to discs on {100} planes. The magnitude of the strengthening, its concentration dependence, and its response to heat treatment are adequately explained by a model which attributes initial resistance to dislocation motion to coherency strains set up by a distribution of very fine precipitates. With particle growth, strengthening first increases until at a critical particle size Orowan looping becomes dominant; thereafter softening occurs with further growth.     

Mechanical properties of spinodally decomposed Fe-30 wt% Cr alloys: Yield strength and aging embrittlement

The age-hardening due to spinodal decomposition in Fe-30 wt% Cr alloys was studied. The yield stress was measured using monotonic tensile tests over a temperature range from 77 to 473 K. The observed incremental yield stress was found to be essentially test temperature independent, increasing substantially with increasing aging time as long as deformation occurs by a slip dominant mode. TEM observation of these test samples showed many dislocation pile-ups for aged materials while as-quenched materials exhibited a homogeneous dislocation distribution. The composition profile and consequent internal stress field due to isotropic decomposition were simulated using Cahn's multi-wave method. The results of this model were then used to estimate the yield stress for such an isotropic decomposition. Theory and experiment were compared using estimates of the extent of decomposition derived from detailed analyses of small angle neutron scattering (SANS). The results indicated that the misfit effect due to the coherent internal stress field is the dominant mechanism responsible for the observed age hardening. Experimental observations are consistent with a model for aging embrittlement which attributes the origin of twinning deformation to a Cr-rich second phase with Cr concentration greater than some critical value.     

Effect of cerium on structure,magnetism and magnetostriction of Fe81Ga19 alloy

FeGa alloy is a new kind of magnetostrictive material, and rare-earth cerium can improve its magnetostrictive property.(Fe_(81)Ga_(19))_(100-x)Ce_x(x = 0, 0.3 at%, 0.7 at%, 1 at%) samples were prepared by doping cerium in Fe_(81)Ga_(19) alloy. Their microstructures and phases were studied, and valence electronic structures were investigated. Electromagnetic parameters, such as coercivity, saturation magnetization,remnant magnetization and saturation magnetostrictive coefficients(λ_s) of every sample were measured.Cerium atoms are distributed at grain boundaries, and the Ce-doped alloys remain the A2 structure of FeGa alloy. When x is 0.7, the value of saturation magnetism is 217.08 emu/g, which is the maximum in the Ce-doped samples. The equivalent half length of single bond is the maximum also, and reaches to0.11380 nm. At the same time, the number of covalent electrons is 3.5672, and is the minimum of the Cedoped samples. Its As is the largest in the four samples. The change of As results in the change of equivalent half length of single bond in Ce-doped alloy.