High Niobium Research Articles

Improved Conductivity of 2D Perovskite Capping Layer for Realizing High-Performance 3D/2D Heterostructured Hole Transport Layer-Free Perovskite Photovoltaics.

Perovskite solar cells (PSCs) have emerged as low-cost photovoltaic representatives. Constructing three-dimensional (3D)/two-dimensional (2D) perovskite heterostructures has been shown to effectively enhance the efficiency and stability of PSCs. However, further enhancement of device performance is still largely limited by inferior conductivity of the 2D perovskite capping layer and its mismatched energy level with the 3D perovskite layer. Here, we developed an effective surface modification strategy via synergically incorporating inorganic high valence-state niobium ion (Nb5+) metal dopants and organic ammonium halide salts to in situ construct a high-quality 2D perovskite capping layer on top of the underlying 3D perovskite layer. As a result, the conductivity of the 2D perovskite capping layer was effectively enhanced by 43%, the energy barrier between 3D and 2D perovskite layers was favorably reduced, and the built-in electric field of the 3D/2D heterostructured perovskite stacks has been enlarged. In addition, the 2D perovskite capping layer also effectively reduced the defect densities by up to 29%, as verified by the space-charge-limited-current (SCLC) tests. Benefiting from the facilitated charge extraction and suppressed non-radiative recombination, the blade-coated hole transport layer-free PSCs based on this optimized 3D/2D heterostructured perovskite film achieved an efficiency of 23.2%, ∼19% higher than that of the control device (19.5%), which represented one of the best-performing PSCs with simplified device architecture fabricated via a scalable fabrication technique. The modified 3D/2D perovskite-based device also exhibited improved operational stability.

Tribological and Fatigue Behaviour of Ti-Nb-Zr-Sn Alloy through Powder Compacting: Novel Performance of High Niobium Alloys for Bone Tissue Compatibility

Biocompatible materials are natural or man-made substances kept in the body to turn a living cell into a working organ. Bone tissue and biocompatibility are emerging as an alternative approach to regenerating bone due to some distinct advantages over autografting and allografting. This research aimed to fabricate a novel porous scaffold Ti-Nb-Zr-Sn alloy that can be utilized as a bone substitute. Ti-Nb-Sn-Zr were selected by different weight ratios and synthesized using the powder metallurgy method. Zirconium (Zr) is incorporated to get enhanced biological performance. The elements Ti, Nb with Zr, and Sn are utilized due to their excellent biocompatibility with the human body. The Ti-35Nb-7Zr-4Sn alloy has high tensile strength between 1042 and 1603 MPa by ­increasing Zr and Nb weight ratios. In addition, 35% Nb/7% Zr with 4% Sn composite show improved hardness, which is beneficial for resembling bone tissue and die-casting fittings in automobile applications. Fatigue and wear analysis is conducted to help us understand the behaviour of the Ti-Nb-Zr-Sn alloy.

Suppressing the oxygen-ionic conductivity and promoting the phase stability of the high-entropy rare earth niobates via Ta substitution

Improving and optimizing the target properties of ceramics via the high entropy strategy has attracted significant attention. Rare earth niobate is a potential thermal barrier coating (TBCs) material, but its poor high-temperature phase stability limits its further application. In this work, four sets of TBCs high-entropy ceramics, (Sm1/5Dy1/5Ho1/5Er1/5Yb1/5)(Nb1/2Ta1/2)O4 (5NbTa), (Sm1/6Dy1/6Ho1/6Er1/6Yb1/6Lu1/6)(Nb1/2Ta1/2)O4 (6NbTa), (Sm1/7Gd1/7Dy1/7Ho1/7Er1/7Yb1/7Lu1/7)(Nb1/2Ta1/2)O4 (7NbTa), (Sm1/8Gd1/8Dy1/8Ho1/8Er1/8Tm1/8Yb1/8Lu1/8) (Nb1/2Ta1/2)O4 (8NbTa) are synthesized using a solid-state reaction method at 1650 °C for 6 h. Firstly, the X-ray diffractometer (XRD) patterns display that the samples are all single-phase solid solution structures (space group C2/c). Differential scanning calorimetry (DSC) and the high-temperature XRD of 8NbTa cross-check that the addition of Ta element in 8HERN increases the phase transition temperature above 1400 °C, which can be attributed to that the Ta/Nb co-doping at B site introduces the fluctuation of the bond strength of Ta-O and Nb-O. Secondly, compared to high-entropy rare-earth niobates, the introduction of Ta atoms at B site substantially reduce thermal conductivity (reduced by 44 %, 800 °C) with the seven components high entropy ceramic as an example. The low thermal conductivity means strong phonon scattering, which may originate from the softening acoustic mode and flattened phonon dispersion in 5–8 principal element high entropy rare earth niobium tantalates (5–8NbTa) revealed by the first-principles calculations. Thirdly, the Ta/Nb co-doping in 5–8NbTa systems can further optimize the insulation performance of oxygen ions. The oxygen-ion conductivity of 8NbTa (3.31 × 10−6 S cm−1, 900 °C) is about 5 times lower than that of 8HERN (15.8 × 10−6 S cm−1, 900 °C) because of the sluggish diffusion effect, providing better oxygen barrier capacity in 5–8NbTa systems to inhibit the overgrowth of the thermal growth oxide (TGO) of TBCs. In addition, influenced by lattice distortion and solid solution strengthening, the samples possess higher hardness (7.51–8.15 GPa) and TECs (9.78 × 10−6 K−1–10.78 × 10−6 K−1, 1500 °C) than the single rare-earth niobates and tantalates. Based on their excellent overall properties, it is considered that 5–8NbTa can be used as auspicious TBCs.

Pulse current diffusion bonding of high niobium β-γ TiAl alloy to IN718 superalloy by introducing pure Ni interlayer

High niobium β-γ TiAl alloy (HNBG) was pulse current diffusion bonded to Ni-based superalloy (IN718) by introducing Ni foil as an interlayer using spark plasma sintering (SPS). Typical microstructure characteristics and mechanical properties of HNBG/Ni/IN718 joint were investigated in detail. The effects of bonding parameters and Ni interlayer on microstructure and mechanical properties were revealed, and the diffusion bonding mechanism of HNBG/Ni/IN718 joint was elaborated. The phase composition sequence from IN178 superalloy to HNBG alloy was IN718//γ-Ni//γ′-Ni3(Al, Ti)//τ4-Ni2AlTi//τ3-NiAl3Ti2//β/B2 + τ3-NiAl3Ti2//HNBG. The Kirkendall voids and interfaces gradually disappeared with increasing bonding temperature, time and pressure. The maximum shear strength of 346 MPa was achieved at 850°C × 20 min × 20 MPa. The introduction of Ni interlayer significantly improved the elemental distribution and microstructure, which enhanced shear strength of HNBG/Ni/IN718 joint by 34.6 % compared to that of the joint without any interlayers. Shear fracture mainly occurred in γ′ diffusion layer, and fracture mode was brittleness transcrystalline fracture when the bonding temperature was lower than 850 °C. As the temperature increased, fracture mainly occurred in τ3 diffusion layer, and the fracture mode was cleavage fracture.

Diffusion bonding behaviour of Nb–Si and TiAl alloys by spark plasma sintering

Nb–Si alloy and high niobium β-γ TiAl alloy(HNBG) was joined by diffusion bonding ranging from 1000 to 1100 °C at 10 MPa for 20 min by spark plasma sintering. The phase sequence from HNBG to Nb–Si side was HNBG||β/B2+α2-Ti3Al||δ-(Nb, Ti)3Al+σ-(Nb, Ti)2Al + Ti rich γ-(Nb, Ti)5Si3||Nb–Si in the joint. The sound joints without any pores were obtained with the bonding temperature above 1050 °C. The nano-indentation test results showed that Ti rich γ-(Nb, Ti)5Si3 and σ-(Nb, Ti)2Al phases had relatively high hardness and elastic modulus in the diffusion zones II. The highest shear strength of 269 MPa was achieved at 1050 °C. Fracture mainly occurred along the interface of the diffusion zones due to low interfacial adhesion induced by lower bonding temperature. As the bonding temperature was higher, the cracks propagated mainly from in the interface to through the phases due to the increase of interfacial adhesion. The joining mechanism of HNBG/Nb–Si joint was analysed through diagram.

Diffusion bonding behaviour of β-γ TiAl alloys containing high niobium with Ti interlayer by spark plasma sintering

High niobium β-γ TiAl alloy (HNBG) was diffusion bonded using spark plasma sintering with pure Ti as interlayer. The joint microstructural evolution, growth kinetics and mechanical properties were investigated. The joint included three diffusion zones. The β/B2 phase formed in the Zone I, α2 phase in the Zone II, and β-Ti and α-Ti phases in the Zone III. The thickness of β/B2 phase, the average grain size of α2 phase and the amount of β-Ti phase increased with the increase of bonding temperature or bonding time. The growth activation energies of β/B2 and α2 phases were 582 and 253 kJ/mol, respectively. The joint acquired at 1000 °C, 10 min and 10 MPa showed the maximum shear strength of 308 MPa. Fracture mainly occurred along the interfaces between Zone I and HNBG alloy, and between Zone I and Zone II. Fracture mechanism of the joint was characterized by brittleness rupture along the phase boundary.

Microstructure and mechanical properties of high niobium β-γ TiAl and IN718 alloy joints diffusion bonded by spark plasma sintering

High niobium β-γ TiAl alloy(HNBG) was diffusion bonded with Ni-based superalloy (IN718) from 800 to 900 °C for 20 min under the pressure of 10 MPa by spark plasma sintering. The joint phase composition, growth kinetics and shear mechanical properties were investigated detailedly. The phase sequence was HNBG//β/B2, τ3-NiAl3Ti2//τ3-NiAl3Ti2//τ4-Ni2AlTi, σ-FeCr//Cr/Fe/Nb rich η-Ni3Ti, α-Cr, Cr rich γ-Ni/γ′-Ni3(Al, Ti)//IN718 in the joint. The growth activation energies of diffusion zones on the IN718 side were lower than that on the HNBG side. The molecular dynamics result showed that the dislocation density increased with bonding temperature on the IN718 side. The nano-indentation test results showed that the phases in the diffusion zones II and IV had relatively high hardness. The ultimate shear strength of 257 MPa was achieved at 850 °C. Fracture mainly occurred along the interface between diffusion zones III and IV with bonding temperature lower than 900 °C, while mainly occurred in the diffusion zone II at 900 °C. The shear failure mechanism of the joint was brittleness fracture along the phase interface and brittleness transcrystalline fracture. Finally, the formation mechanism of HNBG/IN718 joint was analysed.

A study of laves phase in high Nb non-oriented silicon steel for electric automobiles

In the study of precipitates in high-Nb non-oriented silicon steel for the rotor of electric automobiles, it was found that mass dispersed Nb-rich precipitates were formed during the rolling process of the steel, these precipitates are presumed to be Laves phases in published literatures. In this regard, two types of Laves phases of high-Nb non-oriented silicon steel for electric automobiles and their crystallographic relationship with the Fe matrix were determined using SAED, FFT and IFFT, and calculation of steel strength enhancement by precipitation strengthening. The results showed the elliptical Laves phase is Fe16Nb6Si7 and the rectangular strip Laves phase is Nb7P4, and the orientation relationship between Fe16Nb6Si7 phase and Fe matrix is : [001]Fe16Nb6Si7∥[001]Fe, [101]Fe16Nb6Si7∥[110]Fe, [113]Fe16Nb6Si7∥[112]Fe, the orientation relationship between Nb7P4 phase and Fe matrix is : [130]Nb7P4∥[001]Fe, [102]Nb7P4∥[110]Fe, [110]Nb7P4∥[112]Fe; Both Fe16Nb6Si7 and Nb7P4 precipitates have a good coherent relationship with the Fe matrix; The calculation results show that Fe16Nb6Si7, Nb7P4 and other precipitates can improve the yield strength of non-oriented silicon steel, but at the same time, the magnetic properties of the steel are expected to be negatively impacted. The research results can provide important theoretical guidance on the influence of thermo-mechanical processing on balancing the mechanical and magnetic properties of high niobium non-oriented silicon steel for electric vehicle rotor.

Microstructure and Continuous Cooling Transformation of an Fe-7.1Al-0.7Mn-0.4C-0.3Nb Alloy

Reducing pollutant emissions and improving safety standards are primary targets for modern mobility improvement. To meet these needs, the development of low-density steels containing aluminum is a new frontier of research for automotive applications. Low-density Fe-Mn-Al-C alloys are promising. In this regard, an alloy with high aluminum content and niobium addition belonging to the Fe-Mn-Al-C system was evaluated to understand the possible phase transformations and thus obtain a transformation diagram by continuous cooling to help future processing. Dilatometry tests were performed in a Gleeble thermomechanical simulator with different cooling rates (1, 3, 5, 10, 15, 20, 30, and 50 °C/s). Chemical analyses carried out simultaneously with dilatometry tests showed the presence of proeutectoid ferrite (αp), δ-ferrite, retained austenite, and niobium carbide (NbC). In the case of low cooling rates (1 and 3 °C/s), lamellar colonies of the eutectoid microconstituents were observed with a combination of α-ferrite and k-carbide. For higher cooling rates (5 to 50 °C/s), martensite was observed with body-centered cubic (BCC) and body-centered tetragonal (BCT) structures.

Interfacial microstructure and shear performance of TiAl to Nb–Si alloy diffusion bonded with pure Ti interlayer

Diffusion bonding of high niobium β-γ TiAl (HNBG) to Nb–Si alloy was carried out using Ti foil as interlayer. The interfacial microstructural evolution, growth kinetics and mechanical properties of HNBG/Ti/Nb–Si joint were investigated in detail. The microstructure observations indicate that the interfacial microstructure of the joint was composed of β-(Nb, Ti)5Si3, (Nb,Ti)ss//α-Ti, β-Ti//α2//β/B2 from zone I to zone IV. The β-Ti phase and α-Ti phase in zone II obey the orientation relationship, {110}β || {0002}α and <111>β|| <11–20>α. The γ phase in HNBG alloy and β/B2 phase in zone IV obey the orientation relationship, {111}γ || {110}β/B2 and <110>γ || <111>β/B2. The growth activation energies of β-(Nb, Ti)5Si3 and β/B2 phases were 166 kJ/mol and 507 kJ/mol respectively. The content of β phase in zone II and the average grain size of α2 phase in zone III increased with bonding temperature or bonding time. The shear test results showed that the ultimate shear strength was 385 MPa at 1000 °C-10 min-10 MPa. Fracture mainly occurred beween the interface of zone III and IV, and between the interface of zone IV and HNBG alloy. The fracture mode was mainly characterized by brittleness rupture along the phase boundaries of α2 and β/B2, β/B2 and HNBG alloy with slight amount of cleavage fracture in zone IV.

Investigation and performance of high niobium contain Ti-Al Alloys: Deformation behaviour and microstructural evolution

Phase transformation and crystal structure variety will influence microstructure evolution and hot deformation behaviour of high niobium containing Ti-Al alloys. These alloys are great attention in research on industrial and medical sectors. The niobium alloys are lightweight and high strength, increasingly popular for automotive engine and chassis components. Three novel Ti-Al based alloys have been developed in present research such as Ti-43Al-6Nb-1Mo-1Cr, Ti-43Al-7Nb-3Mo-2Cr and Ti-43Al-8Nb-3Mo-3Cr niobium alloys were fabricated using a hot isostatic press (HIP). The alloys were heat-treated at 1200 °C temperature for 5 h in the Ar atmosphere. The mechanical properties and flow curves of Ti-Al alloys are studied by varying three different temperatures (800 to 1200 °C) and strain rates (0.1 to 10 s−1) on a servo-controlled universal testing machine. The microstructures of the alloys were analysed using SEM. The results showed an addition of Nb-Mo-Cr particles to Ti-Al increased material strength by 21.36% (Hardness), 32.08% (compressive), 41.37% (splitting tensile) and 39.23% (flexural) more than as-cast alloy. In addition, Nb and Cr with Mo will provide excellent oxidation resistance and mechanical strength for Ti-Al alloys. This study shows a benchmark against compatible alloys and metallic implants. From results, the representation of material is specified as Ti-43Al-8Nb-3Mo-3Cr > Ti-43Al-7Nb-3Mo-2Cr > Ti-43Al-6Nb-1Mo-1Cr.

Late Cretaceous to Paleocene magmatic record of the transition between collision and subduction in the Western and Central Cordillera of northern Colombia

Deformational field relations, compositional and U–Pb geochronological data of magmatic rocks of the northwestern Colombian Andes provide insights to recognize the different pre to post-collisional stages in an arc-arc collisional scenario until the re-initiation of a new subduction zone. A western belt of undeformed to mylonitized volcanic rocks with flat REE patterns and a weak LREE depletion present similar geochemical features of adjacent oceanic plateau basalts that were intruded by arc-related dykes at ca. 82 Ma, before their accretion to the continental margin. A sequence of greenschist and quartz + muscovite + graphite schist, and their associated mylonitized dikes, are part of the eastern continental arc, and present ages between 69 and 71 Ma, show tholeiitic affinity, flat rare-earth patterns, and Nb–Ti anomalies. These characteristics mark a decrease in the mantle wedge and older crustal signatures during magma genesis, as the oceanic-continent collision was advancing. Both suites were metamorphosed in a high geothermal gradient with temperatures between 490 and 400 °C and pressures between 2 and 4 Kbar. After this metamorphic event associated to the end of the collision a series of dykes intrude the different units at ca. 58 Ma, including basalts and andesites with Nb–Ti anomalies, adakite-like, and high niobium compositional signatures, suggesting that they were probably formed associated with slab melting in a young subduction environment that evolved after 62 Ma, following a ≤7 Ma magmatic hiatus. This magmatic and metamorphic record can be related to an arc-arc collision scenario in which mantle involvement in the late stages of collision influence both the magmatic and thermal regimes.

The investigation of microstructure evolution, deformation behavior and processing performance of the high niobium containing TiAl alloys

Phase transformation and crystal structure variety will influence microstructure evolution and deformation behavior of high niobium containing TiAl alloys. The deformation mechanisms and the processing maps of Ti–43Al–6Nb–1Mo–1Cr alloys have been studied in this paper. The nucleation and growth of recrystallized γ and α grains can dominate the deformation below or above Tα2→α, respectively, in the temperature range of 1100°C-1200 °C. Additionally, the dynamic recovery (DRV) of α phase dominates the deformation in the condition with low strain rates above 1200 °C. In combination with the microstructure observation, the processing maps by Prasad and Murty instability criterion indicates that the suitable processing region with dynamic recrystallization (DRX) is about in the temperature range of 1100°C-1200 °C and the strain rate range of 0.01s−1-0.001s−1. Summarily, various deformation mechanisms have been discussed and the deformation mechanism map has been obtained, based on different types of microstructure analysis.

Effect of magnesium reduction on the oxygen content of pickling niobium powder

Considering the problem of high oxygen content in industrial niobium powder, the oxygen reduction of high oxygen niobium powder with the addition of magnesium is studied. Based on the thermodynamic analysis of magnesium thermal reduction of niobium powder, the effects of reduction temperature, magnesium addition, reduction time, and reduction atmosphere on the oxygen content of pickling niobium powder are studied. The results show that with an increase in the magnesium addition, the oxygen content of pickling niobium powder gradually decreases to a certain value, and then remains unchanged. In a certain temperature range (953–1203 K), with an increase in the reduction temperature, the oxygen content of pickling niobium powder first decreases, and then increases; the best oxygen content is 356 ppm at 1133 K. With the extension in reduction time (2–6 h), the oxygen content of pickling niobium powder first decreases, and then remains unchanged. Finally, the oxygen content of pickled niobium powder is reduced to approximately 356 ppm at 400% magnesium addition at 1133 K for 4 h.

Structure, dielectric, and energy storage behaviors of the lossy glass-ceramics obtained from Na2O-Nb2O5-P2O5 glassy-system

ABSTRACT A series of phosphate glasses defined by the composition 50Na2O-xNb2O5-(50-x)P2O5 (0<x < 25 mol%) and designated as Nb5, Nb10, Nb15, Nb20, Nb25, respectively, have been elaborated by the melt quenching method, and their structural and optical properties were investigated. It was found that their density and molar volume increase and decrease with the Nb2O5 content, respectively. The analysis of the glasses structure by Raman spectroscopy allowed the identification of several phosphate structural units, mainly metaphosphate and pyrophosphate, and showed that niobium adopts an octahedral oxygen environment, forming linkages such as Nb-O-P and Nb-O-Nb within the network. Glass-ceramics were obtained by controlled heat treatments of the parent glasses. The heat treatment of the high niobium concentration glass Nb25 at 650°C led to the formation of the sodium niobate phase with cubic symmetry. Its microstructure was analyzed by SEM. The study of the dielectric properties of the glass-ceramics and their energy storage performance presented an optimum discharge density for the glass-ceramic with 25 mol% Nb2O5 and an energy efficiency of 82.5%.

Niobium Oxide Aerogel-Supported Bifunctional Oxygen Electrocatalysts for Unitized Regenerative Fuel Cells

Proton exchange membrane unitized regenerative fuel cells (URFCs) combine the ability to both produce power (in fuel cell mode) and generate fuel and oxidant (in electrolysis mode) from the same cell. The further development and utilization of URFCs is hindered by the high costs and low stability of bifunctional oxygen electrocatalysts. Distributing the oxygen electrocatalyst on a high surface area support can reduce the loading of the active noble metal (e.g., platinum and iridium) and influence the efficiency and stability of the catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Carbon, which is typically used as a support material, is highly unstable under the conditions required for OER which makes carbon unfeasible for long-term use within URFCs. Therefore, alternative carbon-free catalyst supports are needed. Niobium oxide, Nb2O5, is stable in the oxidative potentials and highly corrosive acidic conditions of URFCs; however, the low electronic conductivity of Nb2O5 significantly limits its use as a catalyst support material. We investigated approaches to obtain high surface area and conductive niobium oxides, NbOx, as stable supports for bifunctional oxygen electrocatalysts. The effects of synthesis conditions, drying methods, and temperature/atmosphere treatments on the structure, morphology, surface area, and electronic conductivity were evaluated. The structure, morphology, composition, and surface area were determined by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and nitrogen physisorption analysis. Sol-gel synthesis and supercritical drying resulted in a NbOx aerogel with high surface area and porous morphology. Thermal treatment of the NbOx aerogel under H2 increased the electronic conductivity of NbOx when compared to the as-prepared NbOx. Different methods to deposit noble metals on the NbOx support were evaluated. The NbOx-supported catalysts were tested as bifunctional ORR/OER electrocatalysts to determine their activity and stability. The development supported bifunctional oxygen electrocatalysts that can provide lower noble metal loadings, higher activity and improved stability under harsh acidic conditions and highly oxidizing potentials furthers the development of URFCs with lower cost, improved performance, and enhanced durability.

Effect of chelation in alkoxide precursors of niobium oxide nanoparticles on photochemical degradation of rhodamine B

In order to control the high moisture sensitivity, niobium ethoxide and niobium butoxide were chelated by bidentate ligands chloroacetic acid and dichloroacetic acid, in 1:1 and 1:2 molar ratios using dry toluene as a solvent. When these parent and tailored niobium alkoxides were subjected to hydrolysis followed by condensation and other sol–gel processing, they acted as precursors to yield nano-scaled niobium oxide particles. These chelated alkoxides and synthesized nanoparticles were characterized by various spectroscopic techniques. The synthesized niobium oxide nanoparticles are a promising choice to be used as photocatalyst under UV-VIS radiation to remove organic pollutants from water because of suitable band gaps. The band gaps of the synthesized nanoparticles were calculated by using Tauc plot. The photocatalytic efficiency of these nanoparticles was investigated over the degradation of common organic textile dye—Rhodamine B, under photochemical conditions. The optimization of various conditions like catalyst loading, dye concentration, pH, temperature, etc. was also studied in order to get maximum output.

Corrosion behavior of alloy 52M and 52MSS weld surfacing

High chromium nickel-based fillers are used in nuclear dissimilar joints or repairs. Due to the risks of ductility dip cracking of Alloy 52 M weld surfacing, a nickel-based filler with a high niobium and molybdenum content (Alloy 52MSS) is expected to enhance the stability of grain boundary and improve the resistance to stress corrosion cracking. In this study, Alloy 52 M and Alloy 52MSS were used in weld surfacing on A508 steel. The results showed that Nb concentrated in the interdendritic region, and Mo gathered around Nb-rich carbide grains. The hardness profile presented similar trends for both filler metals. In potentiodynamic testing, the corrosion potential was increased while the corrosion current density was lowered for 52MSS.Further cyclic polarization testing indicated that 52MSS had the capability to increase the protection potential and reduce the pitting phenomenon. The morphology of 52 M welding surfacing after testing showed a feature of interdendritic corrosion, while the characteristic of 52MSS′ showed a behavior in general corrosion. The Mo addition resulted in the formation of a metastable oxide scale that improved the alloy's corrosion resistance in the trans-passivity region. The 52MSS had a more remarkable ability to prevent the outer surface of weld surfacing from interdendritic corrosion.

Recent Results of High Temperature Vacuum Heat Treatment Program of SRF Resonators at IJCLab

In the framework of ESS, a vacuum furnace dedicated to High Temperature Heat Treatment under Vacuum (VH2T2) of SRF bulk niobium (Nb) cavities was developed and commissioned in May 2016. This furnace is mainly used for the reduction of interstitial hydrogen in niobium. VH2T2 is an effective process for curing SRF cavities from the so-called Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -deases phenomenon, which is due to Nb hydrid formation on the RF surface during the cool down of the resonator to cryogenic temperatures. IJCLab VH2T2 process is done at 650 °C during 10h00. The main differences between IJCLab recipe and the standard VH2T2 (SVH2T2) are 2 folds: 1) SVH2T2 is performed at 800 °C during 3h00, 2) IJCLab recipe is applied to spoke resonators equipped with Ti LHe tank. This process, will be applied to the whole series (26 cavities) of ESS 352 MHz Double-Spoke resonators. More than 28 cavities of various type (ESS Double-Spoke resonators, MYRRHA single spoke, ESS elliptical medium and high β cavities) were successfully heat treated according to our recipe and the last results are reported. Moreover, since 2 years we have launched the R&D program HELOISE with the financial support of IN2P3/CNRS. HELOISE is dedicated to Heat Treatment of SRF niobium cavities: it includes Low Temperature Baking, VH2T2, Nitrogen Infusion and Nitrogen Doping processes. HELOISE main objectives are: 1) understand the complex mechanisms of the physical phenomena involved in heat treatment processes, 2) investigate the effect of the parameters impacting the process, 3) develop and master, at large scale and with good reliability, heat treatment processes in order to produce low RF losses and high gradient SRF bulk niobium cavities. Finally, we will focus on the first experimental data on Nitrogen Infusion we obtained: the corresponding results are reported and discussed.

Microstructure, characterization of interfacial phases and mechanical properties of high Nb–TiAl/Al2O3 joints brazed by novel Nb particle-reinforced Ag–Cu filler alloy

High niobium content TiAl alloys and Al2O3 ceramics were successfully joined using novel Nb particle-reinforced Ag–Cu composite filler. The changes in microstructure brazing at different temperatures were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The corresponding mechanical properties were studied by shear tests. The results showed that the brazed joints prepared at 900 °C can be divided into three zones. The typical microstructure of the brazed joints is high niobium content TiAl/AlCuTi + AlCu2Ti/Ag(s,s)+Cu(s,s)+Nb/Ti3(Cu,Al)3O/Al2O3. The brazing temperature was shown to have a significant influence on the microstructure and reaction layer thickness. After brazing at 810 °C, macrodefects could be observed in the brazing seam. At higher brazing temperatures, brazed joints without any defects were obtained. The addition of Nb particles and the suitable thickness of the Ti3(Cu,Al)3O reaction layer are the main reasons for the high shear strength. When brazing at temperatures higher than 900 °C, the volume fraction of the brittle AlCu(Ti, Nb) phase was increased and a thick Ti3(Cu,Al)3O reaction layer was formed, which deteriorated the shear strength of the joint. The maximal shear strength joint reached 228 MPa at 870 °C for 10 min, which is a substantial increase compared with conventional brazing processes.