Nb Interlayer Research Articles

Developing high toughness laminated HfB2-SiC ceramics with ductile Nb interlayer

Herein, laminated HfB2-SiC/Nb ceramic with multi-layered structure was synthesized via tape casting and spark plasma sintering. Despite minor loss in strength of laminated HfB2-SiC/Nb ceramics (447 ± 12 MPa) compared with that of monolithic HfB2-SiC ceramics (470 ± 16 MPa) following the introduction of ductile weak Nb interlayer, fracture toughness of laminated ceramics reached 14.22 ± 0.6 MPa m1/2, showing an improvement of ∼129% in comparison with monolithic ceramics (6.11 ± 0.3 MPa m1/2). Cooperative toughening mechanisms of crack behavior (deflection and delamination) and plastic deformation (dimples and tear ridges) led to the improvement in toughness. This research provides novel strategy for the development of heterogeneous ceramic–metal layered composites with superior fracture toughness.

Diffusion bonding of hydrogenated TC4 alloy and GH3128 superalloy using composite interlayers

The Nb and Nb/Ni interlayers were designed for the diffusion bonding of the hydrogenated TC4 alloy and GH3128 superalloy joint. Typical microstructure of the TC4-0.3 H/Nb(Ni/Nb)/GH3128 joints were investigated. The effects of holding temperatures and durations on the microstructure evolution of the hydrogenated TC4/GH3128 joints were investigated. The addition of a Nb interlayer can successfully suppress the brittle Ti-Ni phase formation and the maximum joint strength reached 245 MPa bonded at 860 ℃/60 min under 10 MPa. The design of the Nb/Ni interlayer successfully eliminated the unbonded voids and the Ni-Cr layer formed when bonding with a single Nb interlayer. The maximum shear strength of ˜270 MPa was achieved when bonding at 860 ℃ for 80 min under 10 MPa. Fracture mechanism of the hydrogenated TC4/GH3128 joints bonded with two interlayers were analyzed finally.

Laser welding of Ti6Al4V to Cu using a niobium interlayer

A hybrid joint with the Nb interlayer consisting of two metallurgical joining interfaces was obtained by the laser welding induced brazing method. The fusion zone comprising the Ti-based and Nb-based solid solutions formed at the Ti6Al4V/Nb interface, while the diffusion bonding layer comprising the Cu-based and Nb-based solid solutions formed at the Nb/Cu interface. The use of niobium interlayer successfully prevented the mixing of Ti and Cu in the molten pool to avoid the formation of TixCuy brittle phases. The tensile strength of the Ti6Al4V/Cu joints with the Nb interlayer increased to 225 MPa, and the joints exhibited the ductile fracture. The fracture region formed at the Cu side near the Nb/Cu interface.

Joining of Graphite to Copper with Nb Interlayer: Microstructure and Mechanical Properties

Reliable joining of graphite and copper is achieved by means of a multilayer structure: niobium, which is used as stress‐relief interlayer, is joined to copper on one side by transient liquid phase (TLP) bonding and to graphite on the other side, using Ti/Cu foils as a filler alloy. The joints prepared by different parameters are analyzed in terms of microstructure, joint strength, and fracture behavior. With low joining temperature and low Ti content, a ductile banded Cu/TiCu4 layer forms between graphite and Nb by peritectic reaction. The dissolution‐precipitation of Nb in TiC particles can help to reduce the brittleness on graphite interface. The TLP bonding between Nb and copper results in a narrow diffusion layer in copper substrate. The maximum shear strength of joints reaches 32 MPa as using 11.3 wt% Ti at 1000 °C. The fracture modes change from bowl shape cracks in graphite/Cu joints to multi‐step cracks in graphite/Nb/Cu joints.

The Determining Role of Nb Interlayer on Interfacial Microstructure and Mechanical Properties of Ti/Steel Clad Plate by Vacuum Rolling Cladding.

We elucidate here the determining role of Nb interlayer on mechanical properties of Ti/steel clad plate fabricated by vacuum rolling cladding (VRC) as a function of different heating temperatures. A critical analysis on the clad interface via electron probe micro-analyzer, X-ray diffractometer and shear testing were conducted to investigate the influence of TiC, Fe-Nb and TiFe compounds and Nb-Ti solid solution on microstructural evolution and shear properties of Ti/steel clad plate. The inter-diffusion between Ti, C and Fe was effectively restrained by adding the Nb interlayer at heating temperature of 800 °C, and average shear strength of 279 MPa was achieved. With increase of heating temperature, Nb-Ti solid solution was formed at the Ti/Nb interface, which reduced mechanical properties of clad plate at 900 °C. At 1000 °C, TiC and Nb-Fe compounds and Nb-Ti solid solution were formed at the interface, and minimum average shear strength of 152 MPa was achieved. The detailed analysis on the clad interface suggested that ideal shear strength can be obtained through the addition of Nb interlayer and selecting appropriate heating temperature.

Effect of niobium interlayer in dissimilar friction stir welding of aluminum to titanium

The most important issue associated with dissimilar welding is the formation of detrimental intermetallics and consequent reduction in mechanical properties of the weld. It was expected that addition of an interlayer would modify the pattern of the intermetallic formation. The present investigation deals with Friction Stir Welding of aluminum (Al) to titanium (Ti) in presence of niobium (Nb) interlayer. X-ray Computed Tomography results highlighted that fine particles of both Ti and Nb are homogeneously distributed. Large Ti particles are substantially fragmented whereas large Nb particles remain as flakes. Microstructural features of the nugget zone indicated a complex mixing of materials. Jointing had been perceived through elemental diffusion at the interfaces of Al/Ti and Ti/Nb. However, Nb restricted the reaction between Al and Ti, and acted as an efficient interlayer to retard the formation of brittle Al3Ti intermetallic phase. Mechanisms of microstructural evolution in Al side of the weld have been identified as Dynamic Recovery, Dynamic Recrystallization and particle stimulated nucleation. Significant improvement in the tensile ductility had been observed due to the presence of finer particles. The presence of Nb in the weld nugget influences the microstructural evolution and tensile properties of the weld by reducing the formation of intermetallics.

Interlayer engineering for titanium clad steel by hot roll bonding

Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using pure Nb or Mo interlayer at 950 °C with a total reduction ratio of 86.7%. Interfacial microstructure and bonding properties of titanium clad steel plates were investigated by electron microscopy and mechanical tests. The results showed β-Ti, TiC and Fe2Ti reaction phases were generated at Ti/steel interface for the clad plates with no interlayer. Inserting Nb or Mo interlayer can effectively suppress the formation of brittle phases, while the weak bonding joint transferred to Nb/steel or Mo/steel interface. And some micro-voids were found at the interface of Nb/steel and Mo/steel. The improved shear strength of clad plates with Nb interlayer might be attributed to the elimination of brittle phases at bonding interface. The small size and little quantities of the micro-voids at Nb/steel interface had a relatively weak effect on shear strength. However, the large number and big size of micro-voids were responsible for the degradation of shear strength for the clad plates with Mo interlayer.

Effect of macro- and micro-segregation on hot cracking of Inconel 718 superalloy argon-arc multilayer cladding

The hot cracking sensitivity dramatically increases because of the longitudinal macro-segregation of craters and the transverse macro-segregation of welding center in pre-layers. Statistical analysis of the total area, average size and Nb concentration of interdendritic low-melting point Laves phase, the Nb concentration of the γ phase in the dendritic core, and the arm spacing of different sub-regions was used to explore the effects of macro- and micro-segregation of Nb. Solidus and liquidus curves were used to determine the temperature at which solid and liquid phases coexist in different sub-regions, which were combined with Scheil equation curves to identify Nb sources and interlayer transfer, so as to develop a model for the molten pool of subsequent layers. This model explains the effect of transversal and longitudinal macro-segregation in the pre-layer on the Nb concentration of the melt pool of subsequent layers, the dynamic balance of the solidification interface and the relative area of Laves phase in the macro-segregated sub-region of the solidified metal.

Dissimilar metal welding of Ti6Al4V and Inconel 718 through pulsed laser welding-induced eutectic reaction technology

The joining of Ti6Al4V and Inconel 718 constitutes a great challenge, due to the TixNiy, Ti-Cr, and Ti-Fe brittle phases’ formation. For the solution of this problem, niobium was selected as an interlayer and the pulsed laser welding-induced eutectic reaction technology was proposed. Two metallurgical bonding zones based on two different bonding mechanisms were identified for the Ti6Al4V/Inconel718 dissimilar joint. When the laser beam was positioned at the Ti6Al4V/Nb interface, the Ti6Al4V and the Nb sheet were partially melted, for the Ti6Al4V and niobium to be joined through fusion welding, while the atomic interdiffusion and the eutectic reaction were responsible for the joining at the Nb/Inconel 718 interface. No TixNiy, Ti-Cr, or Ti-Fe intermetallics were detected in the weld, demonstrating that the unmelted Nb interlayer acted as a diffusion barrier between the Ti6Al4V and the Inconel 718. The eutectic reaction layer formed at the Nb/Inconel 718 interface with the main microstructure of the Ni-Nb system intermetallics. The welded joints fractured at the reaction layer at the maximum tensile strength of 145 MPa and the fracture mode was cleavage fracture.

Toward improved mechanical, tribological, corrosion and in-vitro bioactivity properties of mixed oxide nanotubes on Ti–6Al–7Nb implant using multi-objective PSO

Recently, the robust optimization and prediction models have been highly noticed in district of surface engineering and coating techniques to obtain the highest possible output values through least trial and error experiments. Besides, due to necessity of finding the optimum value of dependent variables, the multi-objective metaheuristic models have been proposed to optimize various processes. Herein, oriented mixed oxide nanotubular arrays were grown on Ti–6Al–7Nb (Ti67) implant using physical vapor deposition magnetron sputtering (PVDMS) designed by Taguchi and following electrochemical anodization. The obtained adhesion strength and hardness of Ti67/Nb were modeled by particle swarm optimization (PSO) to predict the outputs performance. According to developed models, multi-objective PSO (MOPSO) run aimed at finding PVDMS inputs to maximize current outputs simultaneously. The provided sputtering parameters were applied as validation experiment and resulted in higher adhesion strength and hardness of interfaced layer with Ti67. The as-deposited Nb layer before and after optimization were anodized in fluoride-base electrolyte for 300min. To crystallize the coatings, the anodically grown mixed oxide TiO2–Nb2O5–Al2O3 nanotubes were annealed at 440°C for 30min. From the FESEM observations, the optimized adhesive Nb interlayer led to further homogeneity of mixed nanotube arrays. As a result of this surface modification, the anodized sample after annealing showed the highest mechanical, tribological, corrosion resistant and in-vitro bioactivity properties, where a thick bone-like apatite layer was formed on the mixed oxide nanotubes surface within 10 days immersion in simulated body fluid (SBF) after applied MOPSO. The novel results of this study can be effective in optimizing a variety of the surface properties of the nanostructured implants.

Drawing Die Preparation of Composite Diamond Coating Based on Nb Interlayer

In this paper, the drawing die of cemented carbide WC-Co (Wolfram Carbide-Cobalt) was taken as the substrate which was preprocessed by Murakami solution and aqua regia. DCS (Direct Current Magnetron Sputtering) was adopted to sputter the Nb interlayer in the bore of the drawing die. By using EACVD (Electron Assisted Chemical Vapor Deposition), micro-nanocomposite coating was deposited. Then, specimens were characterized through methods like SEM (scanning electron microscope) and Raman etc. Results indicated that the drawing die showed very smooth coating surface and a compact, uniform structure; the grain size < 50 nm and surface roughness < 10 nm. It can be inferred from the indentation experiment that there was satisfactory adhesion force between coating and the substrate. So, the drawing die can satisfy the working requirement of drawing wires.

Ti-Nb-Cu Stress Buffer Layer for TiC Cermet/304 Stainless Steel Diffusion Bonding

Abstract Vacuum diffusion bonding of TiC cermet/304 stainless steel (304SS) was conducted and Ti-Nb-Cu multi-interlayer was used to achieve active bonding and residual stress relieving. Detailed microstructure characterization and mechanical property assessment were carried out to evaluate the bonding technology. It is found that an obvious transition zone is formed at the interfaces, and the interfacial products are (Ti, Nb), remnant Nb, remnant Cu and Cu(s.s). The shear strength of TiC/Ti-Nb-Cu/304SS joint can be up to 84.6 MPa when it is bonded at 925 °C for 20 min under a pressure of 8 MPa. Failure occurs in TiC cermet near the interface in a brittle manner. The results indicate that Ti/Nb/Cu interlayer can effectively reduce the harmful effects of intermetallic compounds on the joint performance, and the Nb interlayer plays a major role in the relief of the residual stress.

Investigation of the rupture of Ti/Steel laminated composite with soft interlayers

The study presents experimental investigations of the contact hardening effect of thin Cu and Nb interlayers in laminated Ti/Steel composites. The four layer Ti-Cu-Nb-Steel with various Nb and Cu interlayer thickness values was obtained via explosion welding and subsequently heat treated at 600°C for 1.5 hr. The evolution of the microstructure of the interfaces between bonded metals before and after heat treatment was studied during composites tensile loading. FEM simulation was carried out to determine the critical value of the relative interlayer thickness at which the composite tensile strength in transverse to the bond interface direction is higher than of Cu.

Superconducting magnetoresistance effect observed in Co/Nb/Co trilayers under a parallel magnetic field: The importance of matching the width of magnetic domain walls of the Co layers with the thickness of the Nb interlayer

Magnetoresistance effects observed in ferromagnet/superconductor (FM/SC) hybrids, FM/SC bilayers (BLs) and FM/SC/FM trilayers (TLs), have attracted much interest. Here, we focus on the stray-fields-based superconducting magnetoresistance effect (sMRE) observed in Co(dCo)/Nb(dNb)/Co(dCo) TLs with sufficiently thick Co outer layers so that out-of-plane magnetic domains (MDs) and MDs walls (MDWs) emerge all over their surface when subjected to a parallel external magnetic field, Hex, equal to the coercive field, Hc. To explore the conditions necessary for maximization of the sMRE, we focus on the different kinds of the stray dipolar fields, Hdip, that emerge at the interior of the out-of-plane MDs and at the boundaries of MDWs; these have a different inherent tendency to create straight and semi-loop vortices, respectively. In the recent literature, the creation of straight and semi-loop vortices has been addressed at some extent both theoretically [Laiho et al., Phys. Rev. B 67, 144522 (2003)] and experimentally [Bobba et al., Phys. Rev. B 89, 214502 (2014)] for the case of FM/SC BLs. Here, we address these issues in FM/SC/FM TLs in connection to the sMRE. Specifically, we focus on an experimental finding reported recently [D. Stamopoulos and E. Aristomenopoulou, J. Appl. Phys. 116, 233908 (2014)]; strong magnetostatic coupling of the FM outer layers is accompanied by an intense sMRE in TLs in which the thickness of the SC interlayer, dSC, matches the width of MDWs, DMDWs. To investigate this finding, we employ simulations-modeling and energy-considerations and propose two quantitative criteria that facilitate the creation of straight vortices over semi-loop ones. The first focuses on the maximization of the stray Hdip that occur at the interior of the out-of-plane MDs. The second enables the estimation of a crossover between the preferable creation of one kind of vortices over the other. Both criteria respond well, when tested against experimental results. These generic criteria on the interference between dSC and DMDWs can assist the design of cryogenic devices based on FM/SC/FM TLs.

Investigation of Tungsten/Steel Brazing Using Nb Interlayer

Due to its excellent thermal physical properties, tungsten is used as structural material in divertor components of fusion reactors. With the rapid development of the technology, the joining of W to reduced activation ferritic/martensitic steel is required for use as a component according to the design of helium cooled high performance divertors. However, W and steel have remarkable differences in their coefficients of thermal expansion, which results in a large residual stress in the joints during the manufacturing and service and consequently leads to failure of the joint. In order to obtain a sound W/steel joint, an appropriate interlayer material inserted between tungsten and steel is necessary to solve the above-mentioned problem. A brazing process, using a Ni–based foil–type filler and a Nb slice as intermediate materials, was carried out in vacuum at 1150 °C for 30 min to investigate the joining of tungsten and steel. The microstructures, chemical composition, hardness and strength of the joint were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), nanoindentation and tensile strength measurement, respectively. The results show that brazing of W and steel was successfully carried out using a Nb interlayer. The bonding interfaces were bonded well. The average tensile strength of 284 MPa was obtained and all specimens fractured in W near the joining seam, in a brittle fracture mode. The nanoindentation test results indicated that the high hardness of 23 GPa were produced at the W/Ni–based filler brazed seams due to the formation of the Boron–riched phase.

Superconductivity tuned through magnetic irreversibility in two-dimensional Co/Nb/Co trilayers under a parallel magnetic field

In ferromagnetic/superconducting (FM/SC) planar hybrids, a reentrance of the upper-critical field line Hc2(T) is observed close to Tc. The effect is generally ascribed to the so-called domain-wall superconductivity and has been theoretically explored in great detail. Experimental investigations are limited mostly to FM/SC bilayers in which the FM layers host out-of-plane magnetic domains of strong anisotropy and large width (>300 nm), the SC layer is quite thick (>30 nm), and the external magnetic field was applied normal. To expand our knowledge to until now unexplored conditions, we study a series of Co(dCo)/Nb(dNb)/Co(dCo) trilayers under a parallel magnetic field; Co outer layers exhibit out-of-plane magnetic domains of weak anisotropy and small width (<150 nm) and the Nb interlayer is very thin (<20 nm). We demonstrate a strong reentrance of Hc2(T) that can be tuned through the irreversible magnetization processes of the FM outer layers, the two-dimensional character of the SC interlayer, and the matching between the interfering SC and FM length scales. These results refine the nature of the reentrance of Hc2(T) in FM/SC hybrids and can motivate new theoretical and experimental investigations.

Microstructure, morphology, adhesion and tribological behavior of sputtered niobium carbide and bismuth films on tool steel

NbC, Bi and Bi/NbC coatings were deposited on AISI M2 steel substrates using unbalanced magnetron sputtering at room temperature with zero bias voltage. Were studied the phase structure, the morphology, the adhesion and the tribological behavior of the three coatings. The niobium carbide film crystallized in the NbC cubic structure, and the bismuth layers had a rhombohedral phase with random orientation. The NbC coating had a smooth surface with low roughness, while the Bi layers on steel and on NbC coating had higher roughness and a morphology composed of large particles. By using a ductile Nb interlayer good adhesion between the NbC coating and the steel substrate was achieved. The Bi coating had better adhesion with the NbC layer than with the steel substrate. The tribological performance of the Bi coating on steel was not satisfactory, but according to the preliminary results, the produced NbC and Bi/NbC coatings have the potential to improve the tribological performance of the steel.

Absolute supercurrent switch in ferromagnetic/superconducting/ferromagnetic trilayers operating at T > 4.2 K

Artificial (CoO-)Co/Nb/Co trilayers (TLs) are studied by means of magnetization, transport, and magnetic force microscopy measurements. By using these TLs as a model system, we provide definite means to distinguish the exchange-fields and stray-fields based magnetoresistance effects observed in relevant Ferromagnetic/Superconducting/Ferromagnetic (FM/SC/FM) structures. Accordingly, we isolate and exclusively focus on the stray-fields version, to report a complete supercurrent switch, ΔR/Rnor ≈ 100%, achieved at operating temperature T > 4.2 K. Detailed series of Co(60 nm)/Nb(dNb)/Co(60 nm) TLs are studied, in which all crucial parameters that relate to the outer Co layers and to the Nb interlayer were systematically varied to unveil the factors that motivate and/or promote the observed effect. We propose a compact model that fairly captures the underlying physics of the Co(60 nm)/Nb(dNb)/Co(60 nm) TLs studied here and can be generalized to assist understanding of the relevant processes in every kind of FM/SC/FM TLs. The presented results and accompanying model are both provocative for basic research and attractive for the design of cryogenic devices.

Co/Nb/Co trilayers as efficient cryogenic spin valves and supercurrent switches: the relevance to the standard giant and tunnel magnetoresistance effects

Nowadays, Ferromagnetic/Superconducting/Ferromagnetic trilayers (FM/SC/FM TLs) are intensively studied. Here, based on (CoO-)Co/Nb/Co TLs of thin Nb interlayer (below 30 nm) we introduce two classes of low-Tc SC-based cryogenic devices, depending on the thickness of the Co outer layers and the presence of a CoO underlayer. An extended range of Co thickness (from 10 to 80 nm) was investigated and an underlayer of CoO was selectively employed, practically aiming to control in-plane and out-of-plane magnetization processes through utilization of shape anisotropy and exchange bias. To this effect magnetic force microscopy, magnetization and magnetoresistance data are presented. Ancillary atomic force microscopy and Rutherford back scattering data are presented, as well. CoO-Co/Nb/Co TLs of the first class have thin Co outer layers (10–30 nm) and are further assisted by the presence of a CoO underlayer to behave as efficient spin valves (ΔR/Rnor = and ΔR/Rmin = ) under the action of the FMs in-plane exchange fields; the effect is termed superconducting Spin-Valve Effect (sSVE). Co/Nb/Co TLs of the second class have thick Co outer layers (50–80 nm) and without the need of a CoO underlayer act as almost absolute supercurrent switches (ΔR/Rnor = and ΔR/Rmin = 28000%) under the action of FMs out-of-plane stray fields; the effect is termed superconducting Magneto-Resistance Effect (sMRE). The properties of these (CoO-)Co/Nb/Co TLs resemble the behavior of standard FM/normal-metal/FM and FM/insulator/FM TLs that exhibit the effects giant (GMR) and tunnel (TMR) magnetoresistance, respectively. Aiming to utilize the FM/SC/FM TLs studied here into cryogenic applications we thoroughly surveyed their operational H-T phase diagram and discuss how can be used to realize binary (‘0’-‘1’) elemental devices for information management in both read heads and memory units. The underlying physical mechanisms responsible for the sSVE and sMRE observed in the two different classes of TLs, that is CoO-Co/Nb/Co and Co/Nb/Co, respectively and the technical requisites that the SC and FM ingredients should meet are discussed.

In-situ Li7La3Zr2O12/LiCoO2 interface modification for advanced all-solid-state battery

The inherent high resistance of electrolyte/electrode interface in all-solid-state-lithium-secondary batteries (SSLB) poses a significant hurdle for the SSLB development. The interfacial resistivity between Li7La3Zr2O12 (LLZ) and LiCoO2 is decreased by introducing a thin Nb layer (∼10 nm) at this interface. The interface modification approach using a Nb interlayer dramatically improves the discharge capacity and rate capability of a SSLB.