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Water electrolysis will be an essential element of the future energy system, with hydrogen serving as a climate-friendly energy storage medium. To make electrolyzers suitable for market penetration at scale, the cost of manufacturing megawatt electrolyzers must be minimized, with no detrimental effects to their performance and lifetime. Here we show a facile and cost-effective manufacturing method to produce one-piece Ti-based bipolar plates. Low-cost and commercially and readily available feedstock materials (blank sheets, expanded metals and nonwovens) are positively joined using an innovative welding process, diffusion bonding. This approach reduces the contact resistances that can occur with multi-part bipolar plates by around 75%, reducing the number of components and therefore significantly simplifying stack assembly. Ex-situ tests on the contact pressure distribution on the active cell surface reveal a homogeneous pattern with values of about 3.75 MPa (± 1.25 MPa). In a first proof-of-concept, a five-cell short stack with a 100 cm2 active cell area, average cell voltages of 1.71 V at 2 A cm−2 could be achieved using our new stack concept. • Detailed insight into the plate design, construction, production and verification. • Main feature of the novel bipolar plate is the one-piece-approach. • Development of a welding-based production process; elimination of contact resistances. • Approach increases the reliability and decreases the duration of the stack assembly. [ABSTRACT FROM AUTHOR]

The outwards diffusion of Al and Si elements in Al-containing and Si-containing MAX phases endows them one natural advantage to form anti-oxidation layer and strong interfacial bonding strength with different materials, including metals and ceramics. This magic phenomenon allows MAX phases to be used in different areas, such as diffusion and fusion welding, coating and laser cladding layer. In order to give one comprehensive and systematical summarization, this review covers important research work on the atomic-level interfacial evolution of Al-containing and Si-containing MAX phases in air or with metals. This will provide an effective guidance for researchers to select the type and adjust the proportion of A-site elements in MAX phases in reference to the applied circumstances. The interfacial structure between Al-containing and Si-containing MAX phase coatings and metals matrix will be reasonably realized. [ABSTRACT FROM AUTHOR]

• The fatigue performance of Bronze/Steel diffusion welded joints is investigated through tests. • The CDM is applied to calculate the fatigue life of Bronze/Steel diffusion welded material. • Database expansion of ANN models is realized by CDM-FEM and dispersivity of fatigue life. • The transfer learning is employed for the fatigue life prediction of Bronze/Steel diffusion welded material. The bronze/steel diffusion welded (BSDW) bimetallic material is often applied in the rotors of piston pumps to withstand complex alternating loads under high-speed operating conditions. Although diffusion welding is a type of solid-phase welding method to achieve high-quality material connections, the fatigue problems still deserve our attention, especially the very high cycle fatigue (VHCF) and high cycle fatigue (HCF) problems. However, due to the high cost of obtaining data, it is necessary to find an efficient and high-precision fatigue life prediction method for diffusion welded materials with a small sample size. In this study, a novel method continuum damage mechanics − transfer learning method (CDM-TLM) for fatigue life prediction of BSDW material is proposed based on the transfer learning (TL) and continuum damage mechanics − finite element method (CDM-FEM). In comparison with the test results, the predicted values of BSDW material fatigue life all fall within the twice error band of the median values of the test life. The influence of frozen layers during TL and training samples in source and target models on the prediction performance is further discussed. CDM-TLM is an effective life prediction method for high-precision life prediction of BSDW material with a small sample size. [ABSTRACT FROM AUTHOR]

During the service of X80 high-strength pipeline steel, the combined effects of welding residual stress, cyclic loading, and hydrogen complicate the prediction of pipeline fatigue life. This article combines ABAQUS and FRANC3D finite element software to analyze the fatigue crack growth laws of the X80 pipeline with thickness of 22 mm under the combined condition. After heat treatment, the fatigue life of pipelines with annular and axial cracks increased by 19 % and 83 %, indicating that post-weld heat treatment significantly improves the fatigue life of the pipeline. When the crack grows to the outer surface of the pipeline, the fatigue life of a pipeline with a 10 % hydrogen doping ratio is reduced by 77 % compared to one with a 1.5 % hydrogen doping ratio. These findings indicate that toughness of the crack front region is significantly reduced by hydrogen concentration, the crack propagation rate is accelerated, and the fatigue life of the pipeline is significantly reduced. • Combined with ABAQUS and FRANC3D, crack propagation is simulated by using mesh fine division and mesh adaptive updating. • The coupling analysis of welding residual stress, hydrogen diffusion and fatigue crack growth is carried out. • The synergistic effect of residual stress and hydrogen concentration on crack growth is analyzed. [ABSTRACT FROM AUTHOR]

This study investigated the microstructural characteristics and mechanical behavior of diffusion welded nickel-based Alloy 617 obtained by electric field-assisted sintering (EFAS) using various parameters. The interfacial microstructure exhibited different characteristics including good grain boundary (GB) migration across the interface in the samples diffusion-welded at 1100 °C and a flat interface in the samples joined at 1000 °C and 1050 °C. The interface consisted of fine Al 2 O 3 oxides, while precipitation of interfacial M 23 C 6 carbides was not observed. Grain boundaries migrated across the Al 2 O 3 oxides, leaving these oxides within the grains. Graded grain size was observed, with grain coarsening being more significant near the sample surface due to the temperature gradient induced by EFAS. Tensile testing revealed that the specimens fractured in the matrix away from the interface, indicting strong diffusion-welded joints. The peak tensile strength of 807 MPa was obtained in the samples welded at 1000 °C due to minimal grain growth. The materials obtained at 1100 °C exhibited reduced tensile strength but improved ductility. Strain maps revealed by digital image correlation showed alternating high and low strain segments in the samples produced at 1000 °C and 1050 °C, indicating that the flat interfaces with no GB migration were less ductile compared to the matrix. A greater strain uniformity was observed along the bond interfaces with improved GB migration. The hardness reduced near the sample surfaces due to enlarged grains induced by temperature gradient. This study demonstrates that GB migration and enhanced mechanical strength can be achieved in diffusion-welded Alloy 617. [Display omitted] • Diffusion welding of Alloy 617 assisted by electric field exhibited grain boundary migration across the interface. • Al-oxides were identified at the bonding interface while Cr-rich carbides were absent. Grain boundaries successfully migrated across the Al-oxides. • Tensile testing of diffusion-welded Alloy 617 demonstrated fracture occurring in the matrix, while the interface remained intact. • Cracks initiated in the bulk carbides during tensile testing, but crack propagation ceased upon contacting the bonding interface. • A graded microstructure was observed within the materials due to the temperature gradient induced by the electric field. [ABSTRACT FROM AUTHOR]

The direct welding of alumina and zirconia ceramics by ultrashort pulse laser is presented for the first time. Compared to traditional dissimilar ceramic joining techniques such as brazing and diffusion welding, this method shows various advantages, including operation at room-temperature, higher welding efficiency, and negligible impact on base materials. The joint microstructure consists of a combination of Al 2 O 3 and ZrO 2 phases, without new phases detected. By adjusting the laser focal point position, the phase content within joint is effectively regulated, successfully preventing crack formation in alumina substrate. The influence of laser power and welding speed on joint morphology and mechanical property is fully investigated. The highest four-point bending strength of 365.5 MPa and shear strength of 33.4 MPa are achieved. After experiencing thermal cycling test at 1000°C, the joint strength and microstructure does not exhibit significant changes, demonstrating the excellent high-temperature durability of the sample. [ABSTRACT FROM AUTHOR]

An Mo interlayer can effectively enhance the thermal conductivity of diamond-copper composite SPS diffusion welding interface. But the detailed microscopic mechanism underlying this enhancement remains unexplored. This study establishes potential interface models based on the elemental composition at the SPS diffusion welding interface and investigates the impact of the Mo interlayer on thermal conductivity. The analysis, grounded in first-principles calculations, examines interfacial spacing, work of adhesion, electronic state density, and phonon state density. Findings indicate that the formation of Mo 2 C at the interface improves bonding, ameliorates the mismatch in phonon vibration frequencies between diamond and Cu, and thereby increases the interface's thermal conductivity. At the weld interface, the 2s and 2p orbitals of C in Mo 2 C exhibit new hybridization peaks distinct from those of C in diamond, while the 4p orbitals of Mo resonate with these new peaks. This results in strong bonding cooperation between Mo and the carbon in diamond, enhancing interfacial bonding strength. This enhanced bonding provides theoretical guidance for achieving high thermal conductivity in SPS diffusion welded interfaces. [ABSTRACT FROM AUTHOR]

Diffusion bonding of dissimilar metals can lead to the formation of intermetallic compounds during the bonding process, which significantly compromise the mechanical properties of the bonded structures. A comprehensive understanding of both the formation and failure mechanisms of bonding joints is essential for optimizing the bonding process and enhancing mechanical properties. In this study, transient liquid phase (TLP) bonding of DD5 single crystal and GH4169 superalloy was conducted using a BNi-2 filler alloy. The effects of bonding temperature and time on the microstructural evolution and mechanical properties of the TLP joints were investigated. From the perspective of microstructure, distinct diffusion affected zone (DAZ) and isothermal solidification zone (ISZ) form in the TLP bonded joints. The widths of DAZ and ISZ increase with higher bonding temperature and time. Additionally, the size of the fine grains in the DAZ of GH4169 increases with bonding temperature and time, and boron (B) accumulates at the grain boundaries in the DAZ of GH4169. The formation sequence in the TLP bonding joint is found to be (i) melting of BNi-2 filler alloy, (ⅱ) formation of M 5 B 3 -type precipitations, followed by (ⅲ) isothermal directional solidification from the DD5 side to the GH4169 side, and (ⅳ) formation of the γ solid solution. In terms of mechanical properties, the microhardness decreases gradually from the GH4169 side to the ISZ and stabilizes from the ISZ to the DD5 side. The specimen bonded at 1100 °C for 120 min exhibited the highest tensile strength (928.63 MPa) and fracture strain (1.62 %) among three TLP bonding processes, achieving 86.8 % of the tensile strength and 51.7 % of the fracture strain of the BM of DD5. The failure mechanisms of the tensile specimens after different TLP bonding processes were explored with the aid of microstructural observations. This study provides valuable insights and technical support for achieving the reliable bonding between DD5 single crystal with GH4169 superalloy. [ABSTRACT FROM AUTHOR]

This study designed a post-weld aging experiments to improve the room and high-temperature strength in Ti2AlNb diffusion welded joints with high entropy interlayers. Firstly, the interfacial microstructure of the Ti2AlNb diffusion welded joints under different aging processes was investigated, followed by room and high-temperature mechanical property tests to establish the aging process window for the joints. Finally, the precipitation mechanism of the nano-O phase in the diffusion reaction interface (DRI) between Ti2AlNb and high entropy interlayers was analyzed, and the strengthening/toughening mechanisms of the aged joints were elucidated. The results indicate that with the aging temperature increasing, the B2 phase in DRI decomposes into a disordered β phase and nano-O phase, with the nano-O phase uniformly distributed in DRI and maintaining a specific Burgers vector relationship, i.e., (001) O // (1 ¯ 0 1 ¯) β ，[ 1 ¯ 10] O // [ 1 ¯ 11] β. The size of the O phase increases gradually with the rise in aging temperature and time, while the volume fraction decreases gradually. But the tensile strength of the joint decrease with aging temperature and time increasing, whereas the elongation increases gradually. The aging process window for the joint is determined as 770 to 800 °C for a time period of 1 to 6 h. The nano-O phase at the DRI not only impedes dislocation movement, but also undergoes slip and twinning deformation, thereby strengthening and coordinating the plastic deformation of the joint. This research provides design guidelines and theoretical support for diffusion bonding of Ti2AlNb alloy. • The B2 phase in the joint interface decomposes into a disordered β phase and uniformly distributed nano-O phase, which maintained a specific relationship with the matrix phase during aging process. • The tensile strength and elongation of the joint at room temperature increased by 21.7 % and 35.7 %, respectively, while those at 650 °C increased by 11.8 % and 24.4 %, respectively. • The nano-O phase impedes dislocation movement, and undergoes slip and twinning deformation, thereby strengthening the joint and coordinating the plastic deformation of the joint. [ABSTRACT FROM AUTHOR]

[Display omitted] • Progress on joining of (Hf,Zr)B 2 diboride based ultra high temperature ceramics (UHTCs) • Joining of UHTCs for thermal protection, and thermal management. • Interfacial wettability and reactivity of diborides and solid-state diffusion bonding. • Role of Nickel filler on interfacial reactivity, phases, and wettability of diborides. • Molecular dynamics and density function theory to predict wettability of diborides. • Future directions of spark plasma sintering, towards joining of UHTCs. Stringent applications of HfB 2 and ZrB 2 based ultra-high temperature ceramics (UHTCs) for hypersonic and re-entry space vehicles necessitate their joining with ceramics or metallic structural alloys. Brazing is the most used joining method for diborides requiring good wettability; consequently, this article critically reviews the high temperature interfacial wettability of diborides in contact with different metals like Ag, Au, Ni, Cu, etc. Contact angle data of various metals in contact with diboride is summarized in this paper along with the assessment of the underlying wetting mechanisms. Surface oxides, testing atmosphere, and other aspects affecting the wettability are evaluated along with the approaches to improve it. High melting point (∼1450 °C) and lower contact angle (∼20°) of Nickel on diborides makes it a good choice as filler material; thus, a detailed case study considering its wettability, phase diagram etc. is reviewed to elicit interfacial reactivity with HfB 2 and ZrB 2. Molecular dynamic simulation and density function theory predicting the wettability and adhesion of various metals on the surface of diborides are also discussed, which exemplify visualization of the experimentally observed values. Microstructural evolution during different joining methods; i.e. active metal brazing, diffusion bonding, welding etc.; are described in detail providing an insight into the final properties of the joint in terms of interfacial strength (shear and bending strength) and thermal stability (oxidation resistance, plasma exposure etc.). The impact of thermal expansion mismatch, residual stresses, and chemical reactions induced during joining are also highlighted to assist in parameter selection. This article concludes with the summary on the current state of the art in the joining diborides followed by scope for future research directions. [ABSTRACT FROM AUTHOR]

Zircaloy-4, which is used as a structural material for nuclear cladding, requires precise bonding at low temperature in nuclear power applications. We achieved this using diffusion bonding with Ni plating on the surface of Zircaloy-4. We evaluated the performance of joints at temperatures between 650 and 780 °C. At 650 °C, the joint was successfully bonded. The joint exhibited a maximum shear strength of 207 MPa at 780 °C, which was twice as high as that produced by direct diffusion bonding at 700 °C under the same parameters. The interface was analyzed by using a combination of SEM and TEM to identify the presence of multilayered intermetallic compound layers in the joints. We investigated the mechanism of interface generation and determined the sequence of phase formation by Gibbs free energy calculations to be NiZr, Ni 10 Zr 7 , NiZr 2 , Ni 7 Zr 2 , and Ni 3 Zr. Through X-ray diffraction and cross-section elemental analysis of the fractures, we observed that, at lower temperatures, the joint fracture tended to occur in the Ni layer, whereas at higher temperatures, it occurred between Ni 7 Zr 2 and Ni 3 Zr. The utilization of diffusion welding with Ni plating applied to the surface of Zircaloy-4 reduces the joining temperature and enhances the properties of the joint. • Achieving Zr-4/Ni/Zr-4 joint through Ni plating on the surface. • The temperature of vacuum diffusion bonding decreases after Ni plating. • Using Gibbs free energy to determine the generation order of the phases. [ABSTRACT FROM AUTHOR]

A comprehensive model for analyzing the kinetics of void evolution and shrinkage during dissimilar diffusion bonding is proposed based on the sinusoidal profile. The model incorporates atom accumulation at void tip to determine the curvature radius of void neck, and integrates the local effect of surface diffusion to quantify the contribution of surface diffusion, thus avoiding the unrealistic void evolution observed in previous models. Furthermore, the model utilizes a combined diffusion coefficient for multicomponent alloys under the effect of stress and concentration gradients, to determine the interfacial diffusion coefficient for dissimilar joints. In contrast to previous models, the current model demonstrates significant improvements in predicted accuracy, efficiently depicting the realistic void evolution and interpreting the formation of various interfacial voids, which can be applied in various bonding cases, including for the dissimilar base metals with different surface conditions. Simulation results from bonding between austenitic steel and ferritic steel with different surface roughness reveal that interfacial voids predominantly form on the side of the base metal with the rougher bonding surface. Additionally, as surface roughness decreases, the prevailing surface source diffusion and interface source diffusion mechanisms promote void evolution and shrinkage, resulting in a significant reduction of the final bonding time. To achieve a high-quality bonding joint, it's suggested to place the smoother bonding surface on the higher creep-resistant base metal, which can accelerate the void closure process. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present study, super-duplex stainless steel (SDSS) and zirconium alloy (ZrA) was vacuum welded using nickel alloy (NiA) interlayer by the diffusion welding process. The welded joints were processed from 800 to 950 °C in steps of 50 °C using 4-MPa compressive load for 75 min. The joints were characterised using optical microscopy, scanning electron microscopy, electron probe micro-analyser, and x-ray diffractometer. The SDSS│NiA interface is planar in nature for all welding temperatures; however, layer-wise Ni 5 Zr, Ni 10 Zr 7 , NiZr, and NiZr 2 reaction products were observed at the NiA│ZrA interfaces. The reaction products and width of these products increase with welding temperature. At both the interfaces, hardness values gradually increase with an increase in welding temperature. NiA│ZrA interface exhibited higher hardness as compared to the SDSS│NiA interface due to the presence of layer wise intermetallics. Joints reached a maximum tensile strength of ∼370 MPa (with an elongation of ∼7.9 %) when the joints were processed at 900 °C due to optimal reaction zone width and the least embrittling effect of the respective intermetallics. At lower temperatures, fracture surfaces of welded assemblies showed featureless morphology and voids present due to the poor coalescence of mating surfaces. At higher welding temperatures, the fracture surface of the transition joint preferred brittle fracture mode due to the cleavage planes with different alignments with insignificant volume fraction of voids on the fractography. • People's material and nuclear material joined using interlayer engineering. • Study reported diffusion-welded joints (DWJs) with sound metallurgical interfaces. • Study is the first type to report tensile properties of DWJs of Zr alloy & SDSS. • DWJs processed at 900 °C favoured the highest tensile strength (∼370 MPa). • Equiatomic Ni–Zr intermetallic (NiZr) requires the least activation energy for growth. [ABSTRACT FROM AUTHOR]

In connection with the possible use of laser technological equipment in space the impact of nanosecond UV laser on copper and its alloys was investigated. At the pre-threshold mode, in the absence of obvious traces of melting, at an energy density of E = 0.1–1.0 J/cm2, the metal in the irradiated zone swelled up and traces of plastic deformation were found. The uplift arised as a result of the formation of an excessive number of point defects. With an increase of the number of impacting pulses, accumulation of damage occurred, despite the fact that the surface completely cools down during the time between pulses. The height of the resulting uplift reached 1 μm, and sometimes even slightly more. Sliding and cracking along grain boundaries occurred, as well as crystallographic slipping. The discovered effect of the impact of laser pulse on the metal surface, associated with the occurrence of uplift and the presence of plastic deformation, is similar to the well-known acoustoplastic, electroplastic, and magnetoplastic effects. The discovered effect was called optoplastic. Exceeding the laser damage threshold (E ∼ 1.0 J/cm2) leads to melting and evaporation of the metal with the formation of a crater. This is oppositely directed process, which suppresses the manifestations of the optoplastic effect. • Copper surface modification due to nanosecond laser pulses impact was investigated. • An optoplastic effect was found. • It is of interest for the preparation of a metal surface for diffusion welding. [ABSTRACT FROM AUTHOR]

The paper investigates the possibility of improving the technology of diffusion welding, which can be used both for joining dissimilar materials for the manufacture of complex devices in the aerospace industry on the ground, and for repair and design in outer space. A laser treatment by nanosecond laser pulses of the ultraviolet range was carried out for surface modification of industry alloys (CrNi55CuВZn, steel AISI 316, Cu–Cr bronze) used in space technology due to high values of thermal and electrical conductivity. It was shown that the preliminary laser treatment leads to an improvement in the properties of the weld: an increase in tensile strength by more than 10%, and tensile strain by more than 20% for certain joints of materials. Also, laser pre-processing can improve the productivity of the welding process, in particular, reduce the temperature and shorten the welding time. • Preliminary laser treatment of alloy samples for diffusion welding was studied. • A method of direct micro- and nanostructuring was used for surface modification. • Laser treatment improves mechanical properties of welded joints used in space and aviation technologies. • Tensile strength increases by more than 10% for joints with treated samples. • Laser pre-processing can reduce the welding temperature and shorten the welding time. [ABSTRACT FROM AUTHOR]

High-density polyethylene (HDPE) pipes have been continuously improved by the progress made by the resin industry and pipe manufacturers. Together with the advanced technology of welding equipment in terms of structure reliability and automations, HDPE pipes have been gradually applied to higher pressure level, bigger diameter, and thicker walls in operations which have become the preferred piping system for nuclear safety application in transporting cooling seawater. There are substantial differences in parameter settings when applying heat and force during different welding procedures, as well as the complicated evaluation methods for mechanical properties, which causes communication barriers between engineers and researchers. Thus, it is necessary to comprehensively study the welding procedures and evaluation methods to standardize the evaluation protocols in the industry. In this paper, based on the assumptions of temperature effect and molecular chain diffusion dynamics at the welding interface, the optimization of the welding procedure is proposed. Some well-established evaluation methods have been used for performance assessment and their feasibilities are discussed. The idea of creating crack along the weld interface is adopted as new method to evaluate the material ability of fracture resistance. Specimens with unilateral notch and weld interface crack are proposed and subjected for quasi-static axial tensile test. The fracture stress and fracture energy at the welding interface are used to differentiate the quality of the joint from different welding procedures. The fracture morphologies of the weld interface are analyzed. A complete picture is drawn for the mechanical fracture resistance of the weld interface. The method used in this paper can be corelated to the pipeline design conditions, therefore could be applied to the real-time engineering applications. Moreover, the evaluation method proposed in this paper is simple, reliable, and easy to implement. • New specimens were designed to create fracture along the weld interface. • Weld interface properties were assessed to character the welding joint. • Method for welding procedure improvement was suggested. • Test results can be extended for design considerations in pipe applications. [ABSTRACT FROM AUTHOR]

• Hydrogen diffusion model in X80 pipeline steel girth welded zone was established. • The distribution of hydrogen concentration coincides with the hydrostatic stress. • Residual stress has a greater impact than structural inhomogeneity in diffusion. Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective. [ABSTRACT FROM AUTHOR]

The development of semiconductor integrated circuits has been limited by the low utilization rate of refractory metal sputtering targets. Spark plasma sintering (SPS) technology has shown great superiority in the sintering and joining of materials, which can be applied to the repair of waste targets and improve the utilization rate. In this study, SPS technology was used to sinter-join the high-purity refractory metal W 30Si sputtering powder and the target for integrated circuits to determine the optimal repair process and repair mechanism. The morphological characteristics, grain size, relative density, and Vickers hardness of the repair layer (powder-sintered body) and the target under different joining times were analyzed, and the interface structure and properties of the W 30Si joint were also studied. It was found that the W 30Si joint was composed of WSi 2 and Si phases. The grain size, relative density, and Vickers hardness of the W 30Si powder-sintered body and targets increased with the joining time. When the joining time was 10 min (1200 °C), the W 30Si joint formed a "zigzag" joining interface, and the bending strength, relative density, grain size, Vickers hardness, and thermal conductivity of the joint were similar to those of the pristine target. In addition, the physical model of SPS sintered and joined refractory metal powders and targets was constructed. Studies have shown that the sinter-joining consists of three stages: early stage, middle stage, and late stage. Among them, the middle stage included two steps that may occur simultaneously, namely the sintering of refractory metal powders and the joining of refractory metal powders with the target, involving pressure welding, micro-arc welding, resistance welding, and diffusion welding mechanisms. This work can provide theoretical guidance for the optimal design of the SPS repair process for refractory metal W 30Si sputtering targets. • The sinter-joining of W 30Si powders and target was realized by SPS technique, and the best repair process was determined. • The repair mechanism of W 30Si target was revealed. After repair, W 30Si joint formed a zigzag connection interface. • The physical model of sinter-joining of W 30Si powders and target was established. [ABSTRACT FROM AUTHOR]

In this work, a copper–brass hetero-laminate with dual-heterostructured interfaces was fabricated by diffusion welding in combination with cold deformation and annealing. These dual-heterostructured interfaces possess the characteristics of both gradient interface and sharp interface. The evolutions of geometrically necessary dislocations (GNDs) and local strains near these dual-heterostructured interfaces were investigated by in-situ and quasi in-situ tests. By employing a constitutive model, the evolutions of GND density and the HDI synergistic strengthening mechanism were systematically explored. The results demonstrated that the distribution of GNDs and local strains near the coarse/fine-grained interface exhibited a gradient feature, without any obvious concentrations of GNDs and strains, which can be attributed to the transition effect of the gradient interface. Furthermore, the density of sample-scale GNDs accumulated near the coarse/fine-grained interface was found to be at least one order of magnitude lower than that of grain-scale GNDs accumulated near grain boundaries. Both the constitutive model and experimental results confirmed that grain-scale GNDs serve as the primary origins of significant HDI stress, rather than the sample-scale GNDs. • GND density and local strains distribute in gradient manner near the coarse/fine-grained interface. • Numerous grain-scale GNDs accumulate around GBs to accommodate the strain gradient between adjacent grains. • A small number of sample-scale GNDs accumulate around the coarse/fine-grained interface. • HDI strengthening originates largely from the accumulation of grain-scale GNDs, rather than the sample-scale GNDs. [ABSTRACT FROM AUTHOR]

Heterostructured laminates have attracted significant attention in the materials community owing to their exceptional combination of strength and ductility. However, long-standing questions remain regarding the impact of the strength difference between the soft and hard layers on the synergistic strengthening in hetero-laminates with weak mechanical heterogeneity; the role played by soft/hard layers with various dislocation storage capacities on the strength–ductility synergy is also poorly understood. In this study, a series of typical heterostructured copper–brass laminates were fabricated using the diffusion welding + forging + rolling + annealing technique. The results demonstrated that larger microstructural and mechanical heterogeneities improved the strength–ductility combination of the hetero-laminates. The relatively weak mechanical heterogeneity and superior dislocation storage capacity of the soft copper and hard brass layers facilitated inter-layer synergistic deformation. This induced a gradual distribution of local strains and geometrically necessary dislocations (GNDs) near the hetero-interface. Thus, when evaluating the role of soft layers in synergistic strengthening, it is crucial to consider their generation and storage capabilities for dislocations. [ABSTRACT FROM AUTHOR]

Reactivity between SiC and Ir as a function of SiC-crystallinity was investigated by diffusion bonding technique under a vacuum and over the temperature range of 1200–1450 °C. As reaction products, various Ir-silicides and free unreacted-C were detected. Reactivity is strongly affected by the temperature and SiC-crystallinity involving a series of interactions, from "no reaction" to "massive exothermic reactions". In particular, interfacial phenomena are more pronounced by the presence of defects and grain boundaries. Solid state reactions result in formation of fine C-precipitates rearranged in a quasi-periodic microstructure. On the contrary, clustering of highly ordered C-precipitates (C-graphitized) occurs after "massive reactions" take place. A relationship between the degree of graphitization (from 1 to multi-layers of graphene), temperature and SiC crystallinity was found by Raman spectroscopy. 2D-layering phenomenon is enhanced in polycrystalline SiC at high temperature. [ABSTRACT FROM AUTHOR]

• A novel copper/bronze laminate was skillfully fabricated by diffusion welding. • Enhanced impact toughness with a value of ∼151.3 J/cm2 was obtained. • The well-bonded interfaces play an important role in impact energy absorption. • The evolution of its fracture mechanism was systematically elucidated. In this work, a novel copper/bronze laminate was skillfully fabricated by diffusion welding. The impact resistance of such coarse-grained laminate was evaluated by Charpy notched impact testing and the evolution of its fracture mechanism was systematically elucidated. The well-bonded transition interfaces can effectively inhibit crack initiation and propagation under high impact loads. The enhanced impact toughness was achieved from delamination of heterostructured interfaces, which consumed high impact energy. Simultaneously, the coarse-grained copper/bronze layers can consume a large amount of impact energy via undergoing coordinated plastic deformation during the impact process. Consequently, this work broadens the enhancement methods on the mechanical performance of metallic materials by a new structural design strategy. [ABSTRACT FROM AUTHOR]

In current work, various soft/hard copper/bronze laminates with transition interfaces and superior mechanical properties were fabricated by three primary processing steps: diffusion welding, cold rolling and annealing (DCA). The superior combinations of strength and ductility for copper/bronze laminates were mainly attributed to back-stress hardening induced by well-bonded transition interfaces. Back-stress hardening was affected by the microstructures and hardness ratio of soft/hard layers. High density dislocations both in original soft and hard layers can weaken the back-stress hardening (ductility). For the dislocation-free copper/bronze laminates, a reasonable high hardness ratio between hard and soft layers can generate a larger strain gradient so as to produce higher back-stress hardening. This work provides a new structural design strategy for metallic materials to simultaneously improve their strength and ductility. [ABSTRACT FROM AUTHOR]

Abstract Conducting the diffusion brazing cycle at 1120 °C for 45 min led to the completion of isothermal solidification and formation of a single-phase Ni-rich γ -solid solution at the joint centerline. Chromium-rich boride precipitates with blocky and acicular morphologies were detected in the diffusion affected zone (DAZ) of all the bonds. The post bond heat treatment of the brazed joint (HT-3 sample) resulted in complete elimination of DAZ boride precipitates and obtaining high levels of homogeneity across the joint region. Performing the brazing cycle between the solution treatment and the double aging cycle (HT-1 sample), as well as after the full heat treatment of the base metal (HT-2 sample), had a minor effect on the morphology of the joint region. While all the heat treatment sequences raised the microhardness values across the bonding regions, the HT-2 sequence reduced the microhardness levels in the isothermally solidified zone (ISZ). The HT-3 sequence improved the joint efficiency up to the remarkable value of 91%. In the as-brazed sample, the fracture path was observed in the ISZ and a dimple-like morphology was detected in the fracture surface. In HT-1 sample, the fracture occurred within the hard DAZ precipitates and a semi-cleavage morphology was detected in the fracture surface. [ABSTRACT FROM AUTHOR]

Abstract Pressureless joining of SiC ceramics at low temperature was developed using Ti powder interlayer. Phase assemblage and microstructure of SiC joint revealed that the products after diffusion bonding mainly consisted of Ti 5 Si 3 and TiC owing to the comparatively low joining temperature. Additionally, Si and C elements were found to be with higher penetration depth in the Ti interlayer. Benefitting from the lower proportion of the brittle Ti 5 Si 3 phase and porosity, shear strength reached a relatively higher value of 41 MPa after joining at 1200 °C for 30 min. [ABSTRACT FROM AUTHOR]

Abstract Hydrogenation of niobium foil was achieved by cathodic charging and its application as the interlayer facilitates a sound joint of TiAl/Ti 2 AlNb. The microstructure and mechanical properties of hydrogenated niobium were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nano-indentation and thermogravimetry (TG) analysis. It is demonstrated that the plasticity of the surface of niobium interlayer is improved and dislocation density in niobium crystal lattice increases significantly, owing to the process of niobium interlayer hydrogenation and subsequent dehydrogenation. To investigate the effect of the hydrogenation of the niobium interlayer on the TiAl/Ti 2 AlNb diffusion bonding joint, the pure niobium foil was also applied as the interlayer for comparison. The effect of the bonding parameters on the interfacial microstructure evolution and mechanical properties of the joints were systematically analyzed by SEM coupled with an energy-dispersive spectroscopy (EDS) and shear test. The typical microstructure of the joint is found to be TiAl/B2 phase/Nb/δ phase/β phase/Ti 2 AlNb. With the increase of the hydrogen content, bonding temperature, holding time and bonding pressure, the bonding defects decreased and the thickness of the diffusion layer increased correspondingly. The shear strength of joint reached 258.9 MPa at 950 °C for 40 min under a pressure of 5 MPa with the hydrogenated niobium interlayer of 1.0 wt% hydrogen content. Highlights • Hydrogenated niobium foils are obtained by electrochemical charging technique. • Novel hydrogenated niobium was applied to achieve a sound joint of TiAl/Ti 2 AlNb. • Mechanisms for hydrogen-induced enhancement of diffusion bonding are proposed. [ABSTRACT FROM AUTHOR]

Abstract Three different thicknesses of pure Zn interlayers were used in the two-step diffusion bonding between ZK60 magnesium (Mg) alloy and 5083 aluminum (Al) alloy. The effect of Zn interlayer thickness on the microstructure and the mechanical properties of the joints were investigated. The results showed that with the thickness of Zn interlayer increased, the width of the diffusion layers increased and the phase formed in the diffusion layer changed from Mg-Al-Zn ternary compounds to Mg-Zn binary compounds and Al-Zn solid solution. The microhardness of the Mg/Zn/Al joints was lower than that of the Mg/Al joint and the shear strength of the joint was improved by Zn interlayer addition. The maximum shear strength of 38.65 MPa was obtained from the Mg/Zn 50 /Al joint in which the laminar structure of MgZn 2 layer resisted the rapid propagation of cracks. Highlights • Two-step diffusion bonding of ZK60Mg and 5083Al were carried out using different thickness of Zn interlayer. • The bonding process was carried out under solid state conditions. • Mg-Zn IMCs formed in Mg/Zn/Al joints, but its influence on the strength of joints was less than that of Mg-Al IMCs. • The maximum shear strength of bonding sample was 38.6 MPa and the microhardness value of was lower than Mg/Al joint. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new Ni-MOF was firstly explored to in-situ derive the carbon nanotubes. • MOF-derived carbon nanotubes were firstly used as an all-solid-state supercapacitor. • A high specific capacitance of 272 mFcm−2 can be achieved at 0.5 mAcm−2. Abstract A new kind of metal-organic framework (MOF) was firstly explored to successfully derive the carbon nanotubes material. The in-situ growth carbon nanotubes deriving from MOFs were used as an all-solid-state supercapacitor for the first time and exhibited a high electrochemical performance. High specific capacitances of 272 and 168 mFcm−2 can be achieved at 0.5 and 10 mAcm−2, respectively. A high retention value of 100% was kept even after 5000 charge and discharge cycles. Such a high electrochemical performance may be due to the intrinsic properties of the MOF-derived carbon materials, such as high surface area, uniformly porous structure and high electronic conductivity. The present study provided a new kind of MOF precursor to generate the carbon nanotubes material and demonstrated that the MOF-derived carbon nanotubes material may be a promising candidate for all-solid-state supercapacitors in future. [ABSTRACT FROM AUTHOR]

Abstract Commercial pure titanium plates with different grain orientations were successfully bonded to carbon steel plates by diffusion bonding. The Ti/steel interfaces were carefully characterized by scanning electron microscopy, energy-dispersive spectroscopy, electron backscattered diffraction, and X-ray diffraction. The results revealed that TiC was generated at the Ti/steel interface during the diffusion bonding process. The thickness of the TiC layer increased with increasing diffusion temperature and holding time. Furthermore, the orientation of the Ti grains influenced the activation energy for the growth of TiC and affected the thickness of the TiC layer at the Ti/steel interface. The anisotropic growth of the TiC layer was explained by the interstitial diffusion mechanism of C atom in α-Ti. Moreover, the TiC layer acted as a barrier layer at Ti/steel interface, inhibiting the diffusion of Fe atoms into α-Ti. An increased diffusion temperature reduced this barrier effect, leading to the formation of FeTi and Fe 2 Ti at TiC/Ti interface. Highlights • Thickness of TiC at Ti/steel diffusion bonded interface is influence by grain orientation of Ti. • The formation of FeTi and Fe 2 Ti can be suppressed because of formation of TiC. • Elevated diffusion temperature impairs the barrier effect of TiC. [ABSTRACT FROM AUTHOR]

Abstract The effects of irradiation on the precipitation behavior of commercial PH 13-8 Mo maraging steel a.k.a. Corrax are investigated through in-situ ion irradiation. Samples of the alloy in its solution annealed state are irradiated up to 10 dpa at 573 and 773 K using 1 MeV Kr ions, in-situ in a transmission electron microscope in order to probe irradiation effects on the precipitation usually observed in this alloy under thermal aging. Indeed, the alloy is known to develop a relatively fine distribution of precipitates during thermal aging which gives the martensitic alloy its strength. The effects of irradiation are substantiated by comparing with the same material thermally aged at 773 and 873 K for similar amounts of experimental time. Both radiation and thermal aging induced segregation and precipitation are characterized using analytical transmission electron microscopy (TEM) techniques. The diffusion coefficients under irradiation are estimated using the point defect balance equations based on Rate Theory and then compared with the thermal diffusion coefficients, demonstrating the accelerated precipitation of β-phase and Laves-phase in the irradiation case at relatively lower temperature is attributed to the radiation-enhanced diffusion. In addition, a numerical model based on classical precipitate nucleation and growth theories is introduced and shows a relatively good agreement with the experimental results in terms of precipitate density. This study serves to generate baseline data on ion irradiation effects on Corrax to learn how this steel responds to irradiation. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract CrN barrier was deposited between a Ni-electroplating and GH3535 alloy with the goal of prohibiting elements interdiffusion and increasing corrosion resistance in molten FLiNaK (LiF-NaF-KF: 46.5-11.5-42.0 mol%) salt. Results indicate that the Ni-coating apparently improves corrosion resistance of GH3535 in molten fluoride salts, but Cr and Fe diffuse constantly from the alloy to the Ni-coating. They are finally dissolved into the molten salt, causing corrosion of the GH3535 alloy. With a CrN diffusion barrier, however, elements interdiffusion has been completely suppressed and the corrosion resistance is further improved by more than eight times comparing to the CrN-free Ni-coated alloy. Highlights • Ni-coating greatly improves corrosion resistance of alloy in molten fluoride salts. • CrN barrier can inhibit elements interdiffusion and enhance corrosion resistance. • CrN layer remains intact and adheres well to the alloy and coating after corrosion. [ABSTRACT FROM AUTHOR]

Inspired by natural structures like bamboo and bone, the incorporation of heterogeneous fibrous structure plays a significant role in skillfully optimizing their mechanical properties. A set of copper-brass heterostructured fibers has been successfully designed and fabricated by a novel strategy, named DRA (diffusion welding, rotary swaging and annealing). This leads to a significant improvement in the synergy between strength and ductility, which can be attributed to the HDI (hetero-deformation induced) hardening effect caused by the high density of hetero-interfaces. The experimental results found that once the GND (geometrically necessary dislocations) density around the hetero-interface reaches the saturation, some GNDs can spread into the adjacent copper and brass zones to alleviate partial stress concentration. The presence of four-sides interfaces in the fibrous composite restricts the dislocation storage capacity of individual fiber, thereby abundant GNDs accumulating near the hetero-interface to produce significant stress concentration and HDI stress. Simultaneously, the severe stress concentration promotes the initiation and propagation of micro-cracks at the hetero-interfaces. These results lead to a more significant HDI hardening while a faster decrease in the work hardening rate of the hetero-fiber during the later stage of tension. Our findings have significantly enhanced our understanding of the deformation mechanism of heterostructured materials. Additionally, this innovative structural design strategy has proven to be highly valuable in the development of heterostructured materials with substantial potential for various applications. [ABSTRACT FROM AUTHOR]

Energetic multilayers are peculiarized by their self-propagation reactions when giving them a thermal pulse. This work reports the chemical reactions of Ni/Al energetic multilayers can be triggered upon ultrahigh compressive load (stress >1 GPa) at ambient temperature, which is realized by micro-compressions of Ni/Al micropillars with equal molar ratio. Detailed microscopic characterizations evidence monolayer reactions of Ni20Al30 and Ni110Al140 (NixAly: x and y are average thickness of individual layers in nanometer) are triggered, forming a stoichiometric NiAl phase after micropillar compression. The as-observed reactions must be triggered by ultrahigh compressive loads, which aid for nucleation of NiAl grains at atomic intermixing zones of Ni-Al interfaces. Once occurrence, the grain growth is self-sustained by the released heat during NiAl formation. The grain textures depend strongly on the deformation extent. The self-sustained process is terminated until the whole micropillar is reacted. Analogous chemical reactions are not observed in the thickest Ni450Al620 micropillar where atomic intermixing is absent. The comparison highlights the critical role of ultrahigh compressive load to trigger monolayer reactions of Ni/Al multilayers, and could forward the advance of Ni/Al energetic multilayers for diffusion welding purpose. • Chemical reactions of energetic multilayers can be triggered upon ultrahigh compressive load at ambient temperature. • Under ultrahigh compressive load, NiAl intermetallic is nucleated and is grown in self-sustained manner. • Chemical reactions are easier to trigger in Ni/Al micropillars with reduced monolayer thickness. • Severe compressive deformation benefits for NiAl nucleation, leading to evident grain growth in NiAl micropillars. [ABSTRACT FROM AUTHOR]

The development of lightweight high-temperature materials and their processing methods are receiving increasing attention as the need for improved performance and energy efficiency in aero-engines increase. In this study, the γ-TiAl alloy was successfully soundly bonded to Ti 2 AlNb alloy by pulsed high current (PHC) diffusion welding. The effect of different high level (HL)/low level (LL) of composite pulse current on the microstructure and mechanical properties of the joints have been studied. The representative interface microstructure of PHC-950 °C TiAl/Ti 2 AlNb joint was γ-TiAl substrate/diffusion bonding zone/Ti 2 AlNb impacted zone/Ti 2 AlNb substrate. The diffusion bonding zone was composed of continuous equiaxed α 2 grains and a small amount of B 2 and O phases. The α 2 phase in the diffusion bonding zone was mainly transformed from the γ phase in γ-TiAl substrate and the B 2 and O phase in Ti 2 AlNb substrate. The composite pulse current has a significant promoting effect on the diffusion of elements and joint formation. The diffusion coefficients of D Al and D Nb in hot-pressing (HP, without current effect) diffusion welding joint at interface were 2 × 10−14 m 2/ s and 0.92 × 10−14 m 2/ s , respectively. In the representative PHC-950 °C joint with HL/LL = 12/2 cycles (single cycle duration 3.3 ms), diffusion coefficients of D Al-12/2 , D Nb-12/2 at interface were 19.62 × 10−14 m 2/ s , 13.34 × 10−14 m 2/ s , respectively. Increasing the duration of LL would weaken the current effect. The current waveform parameters were tuned to HL/LL = 12/4 and 12/6 cycles, the diffusion coefficients of D Al-12/4 , D Nb-12/4 D Al-12/6 and D Nb-12/6 were reduced to 15.69 × 10−14 m 2/ s , 12.49 × 10−14 m 2/ s , 15.31 × 10−14 m 2/ s and 10.99 × 10−14 m 2/ s , respectively. The PHC-950 °C joints have the highest shear strength of 257.3 MPa at HL/LL = 12/2 cycles, reaching 83.3% of the base material strength. The HP-950 °C TiAl/Ti 2 AlNb joint has a shear strength of 230.5 MPa, reaching 74.6% of the base material strength. The shear strength of PHC-950 °C joints at HL/LL = 12/4 and 12/6 reduced to 205.3 MPa, 195.8 MPa due to insufficient element diffusion and damages the bonding quality. This work provides a strategy that contributes to reduce the thermal damage of base metal and improve the joint forming efficiency. • Pulse high current diffusion welding was demonstrated for the soundly joining of dissimilar materials of γ-TiAl and Ti 2 AlNb alloys. • The effect of the high-level/low-level ratio of the pulse current on the TiAl/Ti 2 AlNb joints has been studied for the first time. • Elemental diffusion coefficient in TiAl/Ti 2 AlNb joints under pulsed current conditions is numerically analyzed. [ABSTRACT FROM AUTHOR]

Tantalum (Ta) coated tungsten (W) targets were prepared by hot isostatic pressure (HIP) diffusion welding in the temperature range from 1250 °C to 1550 °C. The mechanical tensile properties displayed that the bonding strength of the W Ta interface reached the maximum value of 138.3 MPa at 1450 °C. The value of nanoindentation hardness of the W Ta interface are between the values of W and Ta substrates indicating the diffusion layer. W Ta diffusion layers were formed during the HIP, and the thickness of diffusion layers increased with the increase of the HIP temperature. TEM results show that the diffusion layer consists of W Ta solid solution, and crystal plane distances of the diffusion layers were slightly enlarged due to the W Ta solid solution. • Using HIP process to prepare solid Ta cladded W targets for spallation neutron sources. • • A diffusion layer was found at the interface of the W‑Ta composite material. The diffusion layer is a sub-grain with a size of about microns. The thickness of the diffusion layer increases with the increase of the HIP temperature. [ABSTRACT FROM AUTHOR]

Abstract Diffusion bonding, due to improving the dispersion of brittle intermetallic compounds, reducing the process energy and increasing the bonding strength of aluminum-magnesium joints, is widely used. In the present study, the commercially pure aluminum and magnesium bulks were successfully diffusion bonded at different strain values (0, 30 and 60%) at 480 °C and different holding times in two cases of without interlayer and with cold rolled copper interlayers. The results of the microstructural study using scanning electron microscopy (SEM) showed that, in interlayer-used bonding, the increase in the strain value of copper interlayer led to a wider joint diffusion layer. The results of the micro hardness test indicated that the hardness of the bonding interface in interlayer-used bonding, decreased in comparison with the non-interlayer bonding state. Moreover, the shear strength test showed that, as the holding time in the non-interlayer state increased, the strength decreased and in the case of interlayer-used bonding, increased time and strain resulted in increased strength of the Al-Mg bond. By rolling the interlayer to different values, the structural and mechanical properties of the Al-Mg diffusion bonding can be adjusted. Graphical abstract Image 1 Highlights • The shear strength of diffusion bonded Al-Mg increased by using Cu interlayer. • Cold working on Cu interlayer, improved the diffusion depth at Al-Cu and Cu-Mg interfaces. • The shear strength of diffusion bonded Al-Mg increased by increasing the strain value of Cu interlayer. [ABSTRACT FROM AUTHOR]

Abstract This study presents an electrically assisted diffusion bonding (EADB) process as a variation of solid-state diffusion bonding to obtain a wider dissemination of this technique. This concept is an experimental adaptation inspired by the rapidly increasing Joule heat during welding that has already been placed into practice. EADB was studied for a Ti 2 AlNb alloy sheet using a commercially pure titanium (CP-Ti) foil interlayer. An in-house built experimental setup was assembled to implement the EADB concept. The nonuniform temperature profiles of the Ti 2 AlNb alloy sheets under different electric current densities were imaged for reference in the subsequent discussion. Common characterization techniques were used to observe the interfacial microstructures, and the shear property and surface Vickers hardness were tested to assess the joint quality. The results showed that bonding interfaces consisted of the interlayer zone and the transition zone, and the Ti 2 AlNb alloy sheets were completely bonded under high electric current densities in the central zone of the sheet. When the density was increased to 4.58 A/mm2, the average room-temperature shear strength and Vickers hardness value reached the maximum values of 641 MPa and 493 HV, respectively. [ABSTRACT FROM AUTHOR]

Abstract The AlCoCrCuFeNi high-entropy alloy (HEA) coatings after one, two and three layers were laser cladded on the AZ91D substrate. Towards the coating interface, the substrate is composed of Mg dendrites and interdendritic Mg + Q eutectics. The formed coatings can be categorized into a low narrow composite region and a top thick dense HEA region. The dominated microstructures in the dense HEA region are columnar dendrites. Nevertheless, the average primary spacing of columnar dendrites became smaller when the coating grew thicker mainly due to the temperature gradient decreasing slowly. Moreover, the planar morphology at re-melted boundary of each clad layer is absence because of the local conditions being suitable for epitaxial growth. Additionally, it is found that the columnar to equiaxed transition (CET) had occurred in the top area of the three-layer HEA coating. This evolution of the microstructure can be explained by the CET theory combined with the sluggish diffusion kinetics and the abnormal variation of the thermal conductivity with the temperature of the AlCoCrCuFeNi HEA. Additionally, the problem associated with dilution by Mg can be completely suppressed by the HEA coating after three layers. Highlights • AlCoCrCuFeNi multi-layer coatings were laser cladded on the AZ91D substrate. • Columnar-to-equiaxed transition occurred in the top region of three-layer coatings. • Unique properties of HEAs affect microstructure evolution of the formed coatings. [ABSTRACT FROM AUTHOR]

Abstract The novel TiO 2 -Sn/C composite nanofibers have been successfully fabricated by a simple and facile electrospinning process. A small amount of metal tin interacts with TiO 2 nanoparticles in a carbon matrix, which makes TiO 2 -Sn/C nanofibers have the stability of TiO 2 and the high capacity of Sn. At the same time, the TiO 2 -Sn/C nanofibers reveal an improved diffusion coefficient of sodium ions due to a small amount of Sn nanoparticles incorporation. Compared with TiO 2 /C nanofibers, the TiO 2 -Sn/C nanofibers electrode shows significantly improved specific capacity, substantial cycling stability, and remarkable rate capability. It delivers high reversible capacity of 255 mA h g−1 at current densities of 0.05 A g−1 in the range of 0.01–2.5 V vs. Na/Na+, and has specific capacities of 214 and 147 mA h g−1 at current densities of 0.5 and 4 A g−1, respectively. Furthermore, TiO 2 -Sn/C nanofibers electrode demonstrates a discharge capacity 190.8 mA h g−1 with 95.4% retention after 1000 cycles at 1 A g−1 (the initial and second discharge capacity is 483 and 201 mA h g−1, respectively). Even up to 5 A g−1, the discharge capacity of 134.3 mA h g−1 with 83.9% retention is obtained after 1000 cycles. Outstanding electrochemical performance makes TiO 2 -Sn/C nanofibers as a hopeful anode material for sodium-ion batteries and to be applied in the field of large-scale energy storage. Graphical abstract Image 1 Highlights • TiO 2 -Sn/C composite nanofibers (TiO 2 -Sn/C NFs) were prepared for the first time by electrospinning method. • TiO 2 -Sn/C NFs electrode combines the advantages of anatase titanium dioxide and metal tin. • TiO 2 -Sn/C NFs electrode exhibits high capacity, superior rate capability and long cycle life. [ABSTRACT FROM AUTHOR]

Abstract We present a discussion on the influence of high-order transition states on interstitial diffusion in fcc systems using first-principles calculations. In earlier works, only first-order transition states (1TS) were used to compute the diffusivity at the atomic-scale: the direct diffusion between tetrahedral (t) and octahedral (o) sites has been proposed to describe atomic-scale diffusion mechanisms. However, we show here that if this direct diffusion makes it possible to reproduce displacements remarkably well, neglecting higher-order transition states induces an underestimation of the diffusion coefficient at high temperature. We hereinafter revisit the diffusion coefficient of interstitial species in different fcc-systems. The effect of these configurations on atom diffusion in Al, Co, Cu, Ni and Pd, whose only stable sites are the tetrahedral and octahedral positions (H and O atoms) is thus discussed here. We show that if the correction is low, taking into account higher-transition states can modify the diffusivity values at high temperature. Highlights • Diffusion of H and O atoms in fcc systems are studied using DFT calculations. • Diffusion coefficients with and without second-order transition states are compared. • In the case of H atoms, theoretical values match experimental ones. • Theory strongly overestimates oxygen diffusivity. [ABSTRACT FROM AUTHOR]

Abstract Phase equilibria and ordered phase regions in the Ni-Mn-Sb system at 700 and 900 °C and the martensite phase region at room temperature were determined mainly by the diffusion triple method. It was confirmed that single-phase region of the ordered bcc phases exists in a wide composition range of a central part at both 700 and 900 °C and that the region is divided into two regions of half-Heusler C1 b and full-Heusler L2 1 at 700 °C, while the C1 b phase is missing at 900 °C. The B2 + L2 1 phase separation was also confirmed in a certain composition range near Ni-50%Mn, and the iso- M s (= RT) line in the L2 1 phase region was also estimated to be located from 12 to 16 at.% Sb. Highlights • Phase diagrams at 700 and 900 °C in the Ni-Mn-Sb ternary system were experimentally determined. • B2 + L 2 1 two-phase region was detected at both 700 and 900 °C. • Critical compositions of L2 1 / C1 b ordering were determined in Ni 2 MnSb/NiMnSb section. • Existing region of martensite phase at room temperature was estimated by diffusion triple. [ABSTRACT FROM AUTHOR]

Abstract The interfacial microstructure and mechanical properties of SiC ceramic joints diffusion bonded via spark plasma sintering with a powder mixture of Ti 3 SiC 2 and B 4 C were investigated. The content of B 4 C ranging from 0 to 20 wt% was added into Ti 3 SiC 2. Microstructure analysis results indicated that B 4 C in-situ reacted with Ti 3 SiC 2 to form fine-sized TiB 2 , TiC, SiC, and carbon in the joint. The volume fraction of these reaction formed phases and coefficient of thermal expansion of the composite interlayer were calculated. The proper addition of B 4 C (5–15 wt%) was beneficial for the improvement of joint strength. The optimal amount of B 4 C addition was 7.5 wt%. The shear strength of the joint bonded with 7.5 wt% B 4 C addition reached 112.5 ± 8.3 MPa, which was 53.9% higher than that bonded without B 4 C addition. Vickers hardness of the composite interlayer was enhanced with the B 4 C addition. Toughening mechanisms including delamination and kinking of Ti 3 SiC 2 , crack deflection, crack bridging, and crack branching were observed in the composite interlayers. [ABSTRACT FROM AUTHOR]

Abstract Fiber metal laminates (FMLs) which consist of magnesium alloy layers and a continuous carbon fiber-reinforced Zn-Al alloy composites layer (the mass fraction of Al is 8%) were fabricated by the diffusion bonding method. The Zn-Al alloy used as the solder of the FMLs in this paper infiltrated the carbon fiber well and bonded the carbon fiber and magnesium alloy layer tightly. Tensile results indicated an improvement of the tensile strength and elastic modulus by 103% and 41%, respectively, compared with those of the original magnesium alloy sheets. The microstructure of the interfaces between the carbon fiber and Zn-Al, as well as the interface between Mg and Zn-Al, were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). MgZn 2 was formed at the Mg/Zn-Al interface. The component of the C f /Zn-Al interface was nanoscale Al 2 O 3. This research proves the feasibility of joining metal sheets with carbon fiber-reinforced low-melting-point alloy composite sheets to fabricate metallurgically-bonded FMLs. [ABSTRACT FROM AUTHOR]

Abstract The mechanism of hydrogen-induced void closure during diffusion bonding (DB) process of hydrogenated Ti-55 alloy with different hydrogen contents at different temperatures has been investigated. When bonded at 700 °C, bonding ratio and shear strength prominently improve with the increase of hydrogen content, which results from residual hydrogen in bonded sample. Hydrogen can increase the fractions of high angle grain boundaries (HAGBs) and β phase as well as break up original long-strip α grains. However, hydrogen almost escapes from hydrogenated alloy when bonded at 800 °C. Then bonding ratio and shear strength slightly increase with increasing hydrogen content. It attributes to grain refinement and volume fraction increase of β phase. Therefore, residual hydrogen plays a key role in improving diffusion bonding properties during DB process. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Intense, chemically pure ion beams of all alkali elements are important for e.g. surface analysis, accelerator physics and transport studies. • Ionic work functions are important ingredients for describing thermodynamic cycles for the energy balance in energy storage materials. • Ionic work functions, energy landscapes and local/global structure are closely interrelated aspects of solid state matter. Abstract The work function for emission of alkali ions M+ (M = Li, Na, K, Rb, Cs) from two different types of alkali aluminosilicates, MAlSi 2 O 6 and MAlSiO 4 , has been investigated by means of thermionic emission. The work functions w fall in a range between 1.0 and 2.5 eV. The work function decreases in the order w(Li+) > w(Na+) > w(K+) > w(Rb+) > w(Cs+). This decrease is correlated with a concomitant increase in the ionic radius of the alkali ion. The work function also increases with increasing ionization energy of the neutral alkali atom. [ABSTRACT FROM AUTHOR]

Abstract Using Ti/Ni/Ti multiple foils as interlayer, carbon/carbon (C/C) composite was bonded to carbon fiber reinforced silicon carbide (C f /SiC) composite by partial transient liquid phase (PTLP) diffusion bonding process. The multiple gradient structures, i.e. C/C composite | Ti-C reaction layer | Ni-Ti intermetallic compound | residual Ni foil | Ni-Ti intermetallic compound | Ti-C reaction layer | C f /SiC composite, were formed during joining process. All the interfaces are bonded well, except for some micro-pores appeared in the interface between the residual Ni layer and Ni-Ti layer. The shear strength of the joint was 44.7 ± 12.8 MPa at room temperature. The X-ray result indicates that only diffraction peaks of C, TiC x and Ni-Ti Intermetallic compound were observed, while no diffraction peaks of Si were found on the fracture surface. Thus, it could be deduced that fracture occurred in the interfacial area adjacent to C/C composite side. Highlights • PTLP diffusion bonding has been successfully used to join C/C and C f /SiC composite using Ti/Ni/Ti foils as interlayer. • The C/C-C f /SiC joints with multiple gradient structures were obtained by PTLP diffusion bonding. • The C/C-C f /SiC joints can be obtained under low vacuum and low pressure. • The average shear strength of the joint can reach 44.7 MPa at room temperature due to the good interface bonding of joints. [ABSTRACT FROM AUTHOR]

Abstract TC4 titanium alloy was joined with Ni80Cr20 alloy by vacuum diffusion bonding at 950 °C without interlayer. Results indicate that interfacial reaction layer is composed of TiNi, Ti 2 Ni, Ti(Ni, Cr) 3 +Cr ss , and Ti(Al, Ni) s. A higher diffusion rate of Ni than Ti caused the segregation of Ni element across the interface which induced the formation of Ni-poor area near Ni80Cr20 side and generated some Kirkendall voids. Moreover, the accumulated Kirkendall voids acted as the source for micro cracks to initiate and propagate along the interface. The maximum shear strength of joints is 55 MPa obtained at the bonding time of 60 min and most joints fractured near Ni80Cr20 side. The interfacial brittle Ti-Ni intermetallic compounds and porous microstructure of Ni80Cr20 as well as the formation of micro cracks near Ni80Cr20 side facilitated the initiation and propagation of cracks during fracture. Highlights • TC4 titanium alloy was joined with Ni80Cr20 alloy by vacuum diffusion bonding at 950 °C without interlayer. • Higher diffusion rate of Ni than Ti caused the enrichment of Ni in TiNi layer. • The accumulated Kirkendall voids acted as the source for micro crack to initiate and propagate along the interface. • The porous microstructure of Ni80Cr20 and micro cracks near Ni80Cr20 side gave a boost to the fracture of the joint. [ABSTRACT FROM AUTHOR]