Brittle Layer Research Articles

Enhanced strength–ductility synergy of carbon nanotube/Al–Cu–Mg composites via introducing laminate structure and grain modification

Laminate carbon nanotube (CNT)/Al–Cu–Mg composites consisting of alternate ductile layers (coarse or ultrafine grain Al) free of CNTs and brittle layers (ultrafine grain) rich in CNTs, were prepared in the powder metallurgy route. It was found that the strength-ductility of the composites was improved remarkably, as compared with those of uniform composites. Mechanical incompatibility between different layers during tensile deformation produced a large number of geometrically necessary dislocations (GNDs) between the ductile layers and the brittle layers, which inhibited the strain localization, thereby enhancing the strength-ductility. Compared with the laminate composite using the coarse grain Al as the ductile layers, the strength of the laminate composite using ultrafine grain Al as ductile layers further increased by 14%, while the elongation remained unchanged. This was because the ultrafine grain rather than coarse grain of the ductile layers could lead to higher strength and had better coordination with the brittle layers.

Rotational Extension Promotes Coeval Upper Crustal Brittle Faulting and Deep‐Seated Rift‐Axis Parallel Flow: Dynamic Coupling Processes Inferred From Analog Model Experiments

AbstractThe lower parts of warm, thick continental crust can flow in a ductile fashion to accommodate thinning of the upper brittle crust during extension. Naturally occurring continental rifts with a rift‐axis parallel deformation gradient imply an underlying rotational component. In such settings, rift‐parallel crustal flow transports material perpendicular to the direction of rifting. We use analog experiments to investigate rotational rifting and coeval crustal flow. To test the effect of rift‐axis parallel flow on rift evolution, we use different gravitational loads resulting in a range of horizontal pressure gradient magnitudes which drive horizontal lower‐crustal flow. The use of (three dimensional) 3D Digital Volume Correlation techniques on X‐ray CT data combined with 3D Digital Image Correlation techniques applied to topographic stereo images provides detailed insights on the contemporaneous evolution of ductile flow patterns and brittle rift structures, respectively. Our results depict a complex flow field in the ductile lower crust during rotational rifting with: (a) extension‐parallel horizontal inward flow and vertical upward flow that compensates thinning of the brittle upper crustal layer; (b) rift‐axis parallel lateral flow, that compensates greater amounts of thinning further away from the rotation axis; and (c) different degrees of mechanical coupling between the brittle and viscous layers that change during rift propagation. Our analog experiments provide insights into ductile lower crustal flow patterns during rift evolution. The results emphasize the three dimensionality of rifting, which is an important effect that should be considered when estimating the amount of crustal extension from two dimensional (2D) cross sections.

Contribution of Viscoelastic Stress to the Synchronization of Earthquake Cycles on Oceanic Transform Faults

AbstractEarthquake clustering can be promoted by local, regional, and remote triggering. The interaction between faults by static and dynamic stress transfer has received much attention. However, the role of quasi‐static stress interaction mediated by viscoelastic flow is still poorly understood. Here, we investigate whether the tight synchronization of moment‐magnitude 6 earthquakes every about 6 years on distant asperities in the Gofar‐Discovery fault system of the East Pacific Rise may be caused by mechanical coupling within the lithosphere‐asthenosphere system. We build a three‐dimensional numerical model of seismic cycles in the framework of rate‐ and state‐dependent friction with a brittle layer overlaying a viscoelastic mantle with nonlinear rheology to simulate earthquake cycles on separate asperities. The brittle section of the West Gofar fault consists of two frictionally unstable 20 km‐long by 5 km‐wide asperities separated by a velocity‐strengthening barrier, consistent with seismic observations, allowing stress transfer by afterslip and viscoelastic relaxation. We find that viscoelastic stress transfer can promote the synchronization of earthquakes. Even if the asperities are separated by as far as 30 km, synchronization is still possible for a viscosity of the underlying mantle of 1017 Pa s, which can be attained by dislocation creep or transient creep during the postseismic period. Considering the similarities in tectonic and structural settings, viscoelastic stress transfer and earthquake synchronization may also occur at 15’20 (Mid‐Atlantic Ridge), George V (Southeast Indian Ridge), Menard and Heezen transform fault (Pacific‐Antarctic Ridge).

The microbial carbonate factory of Hamelin Pool, Shark Bay, Western Australia

Microbialites and peloids are commonly associated throughout the geologic record. Proterozoic carbonate megafacies are composed predominantly of micritic and peloidal limestones often interbedded with stromatolitic textures. The association is also common throughout carbonate ramps and platforms during the Phanerozoic. Recent investigations reveal that Hamelin Pool, located in Shark Bay, Western Australia, is a microbial carbonate factory that provides a modern analog for the microbialite-micritic sediment facies associations that are so prevalent in the geologic record. Hamelin Pool contains the largest known living marine stromatolite system in the world. Although best known for the constructive microbial processes that lead to formation of these stromatolites, our comprehensive mapping has revealed that erosion and degradation of weakly lithified microbial mats in Hamelin Pool leads to the extensive production and accumulation of sand-sized micritic grains. Over 40 km2 of upper intertidal shoreline in the pool contain unlithified to weakly lithified microbial pustular sheet mats, which erode to release irregular peloidal grains. In addition, over 20 km2 of gelatinous microbial mats, with thin brittle layers of micrite, colonize subtidal pavements. When these gelatinous mats erode, the micritic layers break down to form platey, micritic intraclasts with irregular boundaries. Together, the irregular micritic grains from pustular sheet mats and gelatinous pavement mats make up nearly 26% of the total sediment in the pool, plausibly producing ~ 24,000 metric tons of microbial sediment per year. As such, Hamelin Pool can be seen as a microbial carbonate factory, with construction by lithifying microbial mats forming microbialites, and erosion and degradation of weakly lithified microbial mats resulting in extensive production of sand-sized micritic sediments. Insight from these modern examples may have direct applicability for recognition of sedimentary deposits of microbial origin in the geologic record.

Interfacial evolution and mechanical behavior of explosively welded titanium/steel joint under subsequent heat treatment process

Explosive welding (EXW) has advantages in joining metallurgically incompatible metals due to its high quality and simple process. Successful titanium/steel clad plates fabricated by explosive welding have been extensively reported in recent years. However, no research has been reported on the fabrication of explosively welded TA2/15CrNi3MoV clad plates and the effect of subsequent heat treatment processes on the clad plates. This study aims to clarify the microstructure evolution and mechanical behavior of explosively welded TA2/15CrNi3MoV clad plates during the subsequent heat treatment process. The explosively welded TA2/15CrNi3MoV clad plates were heat-treated in the temperature range of 700–1000 °C for 30 min. The results elucidated that the heat treatment process accelerated the interdiffusion of constituent elements (e.g., Fe, Ti, and C) at the TA2/15CrNi3MoV interface, which formed FeTi, Fe2Ti, and TiC. For the samples heat-treated at 700 °C, a continuous TiC layer was generated at the TA2/15CrNi3MoV interface, which hampered the formation of FeTi and Fe2Ti. However, for the samples heat-treated at 800 °C, the continuous TiC layer was broken up, which resulted in a significant increase in the Fe-Ti layer to 1.21 μm. This microstructure evolution dramatically dropped the tensile strength to 329.2 MPa. For samples heat-treated in the temperature range of 900–1000 °C, the thickness of the brittle Fe-Ti layer dramatically increased and caused a rapid drop in tensile strength.

Deformational in curved fold-and-thrust belts: As a function of backstop shape and basal friction: Insights from analogue modeling and application to the Pamir salient, Hindu Kush region

Curved fold-and-thrust belt (CFTB) is a common structural phenomenon in orogenic belts and accretionary wedges, which has attracted the attention of several geologists. However, the formation mechanism of CFTB, particularly the cause of Pamir salient, has been greatly controversial. Therefore, based on previous studies, CFTB was studied by 12 groups of analogue modeling using the different shapes of the backstop and variable basal friction properties, and different compression velocities. The results show that the formation of CFTB is closely associated with the initial geometric characteristics of CFTB, the strength of the basal ductile layer, and the influence of lateral friction. Although the variation in backstop geometries is dominated by the pure Coulomb wedge, CFTB with completely different structural styles can form because of different boundary shapes. The CFTB formed by lower basement friction strength has a larger deformation range, and the CFTB formed by high strength of basal friction, which is narrow, has a high uplift amplitude, forming a tensile structure around its uplift. A high compressional rate forms the higher arc curvature, and a lower compressional rate forms the smaller arc curvature. Models of a brittle basement with triangular backstop and models with ductile basement and boundary parallel to the compression direction may provide a more reliable explanation for the formation of the forward thrust, backward thrust, and symmetrical pop-up structures of the Pamir salient and its structural vergence from south to north. This study further reveals that initial boundary geometry, stratigraphic structure, and rheology with a difference in brittle and ductile layers will yield more complex structural styles and different kinematic characteristics.

On the microstructures and cracking modes of Cr-coated Zr-4 alloys oxidized and vacuum-annealed at 1000 °C

High-temperature oxidation and elemental diffusion significantly affect the microstructure and mechanical properties of Cr-coated zircaloys under accident conditions, leading to cracking modes different from those of samples with fresh coatings. To clarify the intrinsic mechanisms, in situ three-point bending tests were performed and finite element models were built for the Cr-coated Zr-4 alloys oxidized and vacuum-annealed at 1000 °C. In the case of vacuum-annealed Cr coatings, although numerous microcracks were initiated in the brittle ZrCr 2 diffusion layer under external loading, they could hardly propagate through the Cr coating. Recrystallization and grain growth under the annealing conditions led to significant improvement in the ductility of the Cr coating and its deformation compatibility with the substrate, resulting in the best crack resistance of the coating. In the case of oxidized Cr coatings, oxygen penetrated the Cr coating on the substrate, causing a β-Zr to α-Zr(O) phase transformation beneath the interface at the high annealing temperature. Under external loading, driven by large stresses, the brittle layers of Cr 2 O 3 , ZrCr 2 , and α-Zr(O) were susceptible to microcracking, and some cracks penetrated the Cr coating. However, the crack resistance of the oxidized Cr coating was better than that of the as-deposited coating. • Microstructure evolution and fracture mechanisms of Cr coating were demonstrated. • Different cracking modes of the vacuum-annealed and oxidized Cr coating were observed. • Recrystallization greatly improved the ductility and crack resistance of Cr coating. • Oxidation, Zr-Cr interdiffusion, and phase transformation of Zr promoted crack initiation.

Symmetric and asymmetric intercalation effect on the low-velocity impact behavior of carbon/Kevlar hybrid woven laminates

Hybrid fiber composite laminates with the same materials, manufacturing methods and molding processes may present different mechanical behaviors. In this paper, the effect of intercalation sequence on the mechanical performance of carbon/Kevlar plain laminates were studied. According to different intercalation methods, the hybrid layout was divided into symmetric and asymmetric configurations. It is found that the symmetric intercalation structures (KCCK and CKKC) possess better load-bearing and resilience capacity compared with asymmetric structures (CCKK and CKCK), even better than pure carbon structure (CCCC) under high energy impact. The impact damage volume of symmetric specimens was significantly smaller than that of asymmetric specimens by quantitative micro-CT analysis. The apparent damage index (df and dr) can be used to estimate the internal damage data (dCT, H and V). KCCK, a typical symmetric sandwich-like structure, presented the most slight damage among all symmetric and asymmetric configurations, with shear cracks observed at the brittle carbon fiber core layers, while the delamination cracks between Kevlar-carbon interlayers were away from the central damaged region. In CKCK, interlaminar cracks were formed at each carbon-Kevlar interlayers, which shared and relieved the primary interlaminar crack at the core layers compared with CCKK.

Effect of quench-tempering and laser quenching on the microstructure and properties of high-chromium cast iron

In this paper, quench-tempering (QT) and laser quenching (LQ) treatments were performed on the high-chromium cast iron to obtain better microstructure and mechanical properties. The changes in microhardness, microstructure, retained austenite (RA) content, grain size, phase and elemental content of the QT and LQ samples were compared and analyzed. The results showed that the RA content of the untreated samples was 77.02% and the was 26.8 nm. The QT samples showed an increase in carbide dissolution, gradual rounding from sharp angles, transformation of austenite into martensite, reduction of RA content to 28.48%, average grain size (AGS) of 35.8 nm, increase in surface microhardness by 16.6%, and the friction coefficient was reduced by 6.9%. The LQ samples showed a large amount of fine martensite, daisy-like eutectic carbides and diffusely distributed secondary carbides, and the RA content was reduced to 17.72%, with an AGS of 29.9 nm. Compared with the QT samples, the LQ samples showed a 25.1% reduction in AGS, a 16.5% increase in surface microhardness, and a 9.7% decrease in friction coefficient, which was more wear resistant. However, the hard and brittle surface layer of the LQ samples tended to be a source of cracks during impact, resulting in a final reduction of 8.4% in impact toughness compared to the QT samples.

Centrifuge modelling of ultra-thin high strength steel fibre reinforced concrete pavements

Ultra-thin continuously reinforced concrete pavement (UTCRCP) is an innovative pavement type that consists of a 50 mm high strength steel fibre reinforced concrete (HS-SFRC) layer overlain on a pavement substructure. The thickness results in a flexural stiffness significantly smaller than for conventional concrete pavements. In this paper, the conceptual understanding of the response of UTCRCP to traffic loading was investigated using centrifuge modelling. Simplified pavement models were subjected to a bidirectional moving axle load. The results indicated that axle loading, and not single wheel loading, should be used to investigate the response of UTCRCP as there is significant interaction in substructure deformation caused by the wheels on the ends of an axle. Due to the flexural toughness of the highly reinforced concrete layer, a gap forms between the ultra-thin HS-SFRC overlay and its substructure. Brittle, cemented bases between the HS-SFRC overlay and subgrade should be used with caution, as the flexible nature of the layers above and below the stabilised layer may result in rapid degeneration of the brittle layer.

Enhancing the shear strength of the Au–Ge solder joint via forming a ductile face-centered cubic solid solution layer at the interface

The Au-28Ge (at%) eutectic alloy is a high-performance solder with a melting point of 361 °C. However, the brittle interfacial reaction products layer formed between the Au–Ge solder and substrate (Cu or Ni) is always the weak region. Hence, the joint fails at a relatively low shear strength (∼53 MPa). Here, the Cu–Ni alloys (Ni content is 20, 50, or 70 at%) are designed as the substrates to connect with the Au–Ge eutectic at 400 °C. A classic example is represented by the Au–Ge/Cu20Ni joint, which achieves a shear strength of above 100 MPa after soldering at 400 °C for 10–20 min. Microstructure characterization reveals that a face-centered cubic structured solid solution (FCC) layer forms at the Au–Ge/Cu20Ni joint. In contrast, it is mainly the NiGe or Ni2Ge layer in the Au–Ge/Cu50Ni and Au–Ge/Cu70Ni joints. On the one hand, compared to the brittle intermetallic compound products layer, the FCC layer shows adequate ductility, releasing the local strain incompatibility via pronounced local plastic deformation. On the other hand, the fine NiGe and Ni2Ge precipitation and fine grains make the FCC layer stronger than the solder matrix. Therefore, this products layer is no longer the weak region in the solder joint. As a result, the Au–Ge/Cu20Ni joint achieves outstanding shear strength. This study enriches our fundamental understanding of producing ductile phases to enhance the shear strength of the solder joints by designing alloy substrates.

Prediction of residual stresses within dissimilar Al/steel friction stir lap welds using an Eulerian-based modeling approach

Friction stir welding (FSW) was applied to fabricate dissimilar welds between 5052 aluminum alloy and DP590 dual-phase steel with a lap configuration. The interfacial formation and microstructure were investigated experimentally, and in-process thermomechanical conditions with emphasis on resultant residual stress distribution were numerically studied through a fully coupled three-dimensional (3D) Eulerian-based finite element modeling. The Al/steel thermal-mechanical interaction driven by the rotational pin penetrating the steel produced the serrated bonding interface. The brittle intermetallic layer was formed in the interface, showing distribution discontinuity along the welding direction. The simulation results showed that increasing rotation velocity resulted in higher welding temperature and cooling rate, leading to the increment in the residual stress level of the weld zone. Near interfacial residual stresses exhibited an M-shape in the Al alloy while it showed W-shape in the steel, which originated from the thermomechanical processing condition and the effect of mismatch of thermal expansion coefficient. Increasing rotation velocity decreased the near interfacial compressive stress in the steel side. Numerically predicted residual stresses were in acceptable agreement with those measured using the X-ray diffusion measurement with the cosα method, validating prediction reasonability. Hopefully, the current simulation work will provide a new alternative modeling strategy for predicting residual stress fields within the same or dissimilar FSW.

Numerical modeling of the opening mode fracturing emanating from deformation localization in layered rocks

It is known that rock fracture includes inelastic straining or damage that should localize at a certain loading stage and result in fracture initiation. The details of this process are not clear, and it is frequently omitted in the models by imposing the initial microcracks (seeds) with certain lengths and orientations. Here we investigate 2-D systems of three layers in finite-difference models. The layers subjected to the horizontal extension are separated by cohesive-frictional interfaces and have contrasted properties typical of sedimentary piles. Fractures are initiated in a more brittle central layer in the vicinity of the interfaces with the adjacent layers. It starts with the initially distributed inelastic straining, which then localizes into narrow bands. The damage within these bands is strongly accelerated, resulting in complete material failure locally. Short initial fractures corresponding to narrow bands of failed material are normal to the least local stress. They then propagate from the interfaces to the layer center with further extension. We carefully investigate the impact of different regularization procedures, the grid geometry, and structure on all stages of the fracture process and define the optimal conditions that can be applied for fracture modeling in different structural and loading configurations.

Main Factors of Mesozoic Tectonic Deformation in the Erlian Basin, Inner Mongolia, China: Insights from Physical Modelling

Erlian Basin is a Mesozoic oil and gas-bearing basin in northeast of China. The extension rate, extension direction, and stratum thickness of this rift basin have a clear control on its shape and extension. In this study, we design three sandbox models of the Erlian Basin to represent the effects of changing these three factors. The extension rate controls the timing of secondary fault formation inside the rift basin; a high extension rate promotes faster deformation inside the rift. The extension direction controls the strike of the fault inside the rift; a greater angle between the extension direction and the normal direction of the strike of the rift favors rapid evolution of internal secondary faults. The stratum thickness represents the control of sedimentation on the rift basin; the thinner the brittle layer, the wider the rift. The simulation results also show that the extension direction is the major factor controlling tectonic deformation in the basin. Stratum thickness and extension rate are secondary controlling factors. Additionally, according to geometric and kinematic similarities between typical Mesozoic rift basins in eastern and adjacent areas of China, we suggest that southeastward extension is a possible kinematic mechanism for basin formation.

Combined Crack Initiation and Crack Growth Model for Multi-Layer Polymer Materials.

The current publication deals with the fracture toughness of polymeric multi-layer materials. In detail, the crack initiation and growth, crack arrest, and crack re-initiation of a multi-layer material are examined. The aim is to develop a numerical model for crack initiation and incremental crack growth of a three-layer single edge notched bending specimen that features one brittle layer in a plastically deforming matrix. Crack initiation and crack propagation are modeled using the finite fracture mechanics concept and the energy concept, respectively. No delamination is accounted for and the crack grows in one plane. The experimental observation of a crack initiating in the brittle layer (at 61.4 ± 2.2 N) while the initial crack is blunting can be reproduced well with the numerical model (at 63.6 N) with a difference of <3.6%. The model is ready to be used for different layups to predict toughening mechanisms and damage tolerances in multi-layer materials.

Friction stud riveting (FSR) of thick high-strength aluminum alloy structure

7-series aluminum (Al) alloy is a promising material that can meet the ever-increasing lightweight demand for transportation tools. However, the assembly between Al alloy and steel components brings challenges to the existing stud pre-embedded technology. This study proposes a friction stud riveting (FSR) process to achieve high-performance and high-efficiency embedding of steel studs in Al alloy parts by shank undercut, grooves interlock, and intermetallic compounds bonding. The stud geometry and FSR process were first optimized by evaluating the macro morphology of the joints. Then, the microscopic characterizations were performed to understand the material flow behavior, plastic deformation, and microstructure evolution of the joint induced by the feeding and rotation of the stud. The results indicate that the transient thermo-mechanical coupled FSR process leads to a continuous transition of sliding, mixed sliding-sticking, and sticking contact conditions between the stud and the Al alloy, resulting in a thermo-mechanical affected zone (TMAZ) outside the stud and a trapped Al alloy (TAA) inside the stud with diverse dynamic recrystallization (DRX) states and microstructures. The rotation state evolution and temperature gradients of the material within the TAA create two DRX bands that dominate the fracture behavior of TAA under tensile and shear loads. The strengths of the optimized steel stud-thick Al FSR joints reach 101.3% and 118.5% of the 7A52 Al alloy base material in tensile and shear tests, respectively, which solves the problem of low joining strength between steel stud and Al alloy plate due to the brittle and thick intermetallic compounds layers in conventional stud welding processes.

Titanium-modified plasma nitriding layer and enhanced properties for 42CrMo steel

In order to obtain a nitriding layer with thicker ductile diffusion layer and thinner brittle compound layer, plasma nitriding with titanium addition was carried out at 540 °C for 4 h for 42CrMo steel, the characteristic of titanium modified nitriding layer and the enhanced properties were systematically investigated by optical microscope (OM), scanning electron microscope (SEM), XRD, hardness tester and wear tester etc. The results show that titanium addition can effectively modify the characteristics of nitrided layer, and thus a plasma nitrided layer owning thicker ductile diffusion layer and thinner brittle compound layer and higher surface hardness can be obtained. Titanium addition can significantly decrease the compound layer and increase the effective hardening layer, and also greatly enhance the surface hardness, especially with the optimal amount of 0.8 g, the compound layer can be reduced from 19 μm to 10 μm, while the effective hardening layer can be increased from 225 μm to 370 μm. And the surface hardness can be enhanced from 703HV0.05 to 889HV0.05, more importantly, both wear resistance and toughness can be greatly promoted by the novel titanium modified plasma nitrided layer, attributed to the formation of dispersedly distributed TiN particles with very high hardness in the nitriding layer.

Self-organization of magma supply controls crustal thickness variation and tectonic pattern along melt-poor mid-ocean ridges

In nature, variations in mantle sources and magmatic processes lead to significant changes of crustal thickness distribution and spreading pattern at mid-ocean ridges. Distributions in crust thicknesses are relatively uniform at fast ridges. On the contrary, great lateral fluctuations with even mantle rocks exhumation are observed at slow and ultraslow ridges. Similarity, the spreading pattern changes from symmetric configuration (at fast ridges) to highly asymmetric plates accretion with detachment faults and oceanic core complexes (at slow ridges). Recent modeling studies suggested that magmatism may play a key role in the variation. Yet, the physical mechanisms controlling spatial-temporal distribution and intensity of the magmatic activity at mid-ocean ridges remain elusive. In this study, using 3D self-consistent magmatic-thermomechanical numerical models, we systematically investigate the effect of mantle potential temperature and spreading rate on the crustal thickness lateral variations and tectonic pattern at spreading ridges of various opening rates. Our numerical results show that along melt-poor slow-ultraslow mid-ocean ridges, there are two fundamentally different types of ridge sections that spontaneously form and alternate. This is due to a tectono-magmatic instability which self-consistently partitions melt supply beneath the ridge. Two geometries form: (1) normal ridge sections (NR) with elevated topography, normal thickness of oceanic crust and a hot thermal structure, and (2) fracture zone sections (FZ) with lowered topography, thin/absent crust, exhumed mantle rocks, and a cold thermal structure. The tectono-magmatic instability along spreading ridges is triggered by the combined effects of a reduced melt supply from the mantle into crustal magma chambers and an increase in brittle layer thickness. Such bimodal structure is then maintained by the combined effects of buoyant melt partitioning along the ridge, localized latent heat release from crustal magma crystallization, and different spreading modes. This results, on one hand, in hotter, thinner and elevated magmatic sections (tectono-magmatic spreading), and, on the other hand, in colder, thicker and subsided amagmatic sections (purely tectonic spreading). This predicted bimodal distribution finds a good agreement with natural observations. This suggests that spontaneous self-organization of magma supply controlled by spreading rate and mantle potential temperature plays a critical role in shaping tectonic and crustal patterns of mid-ocean ridges.

Silver particle interlayer with high dislocation density for improving the joining of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ electrolyte and AISI 441 interconnect

One of the critical challenges for the protonic ceramic fuel cell stack is sealing electrolytes and interconnects. However, the traditional AgCuO sealant will aggravate the oxidation along the interconnect surface and result in brittle compound layers at the BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolyte interface. The present work demonstrates that a silver particle interlayer with high dislocation density can be adopted to join BZCYYb electrolyte to the interconnect (AISI 441 stainless) in air instead of traditional AgCuO sealant. Elevating temperatures result in a sufficient bonding at the Ag/BZCYYb interface, and a defect-free joint is obtained at 950 °C. Atomic bonding at Ag/BZCYYb interface is confirmed by TEM. Also, a dense and thin oxide layer (2–3 μm) is formed along the AISI 441 interface. Ag particles in the interlayer provide the main driving force for the sintering joining. The massive dislocations promote the recovery and recrystallization of the Ag interlayer, as well as the interdiffusion of BZCYYb/Ag. After aging in the wet oxidizing atmosphere at 600 °C for 300 h, joints remain intact and dense, indicating superior oxidation resistance and aging performance. Besides, the joint shear strength (25.3 MPa) is 59 % higher than that of the joint brazed by traditional AgCuO.

Investigation into the Intermetallic Layers in Ti/Al Multi-Layer Composites Produced via Accumulative Rolling and Sintering

For anti-penetration applications, multilayer composites combining hard brittle elements confronting penetrators and ductile materials at the back are attractive. Because of the weak connection between the ductile and hard brittle layers, these composites usually lose their anti-penetration capability when the hard, brittle layer falls apart. In the present work, attempts to produce in-situ hard, brittle layers were carried out through accumulative roll bonding (ARB) and post-sintering. It is found that an intermetallic interlayer of TiAl3 can be produced between Ti and Al plates with full integrity under a proper sintering condition. The diffusion mechanism between Ti and Al layers was analyzed via microstructural characterization. It implies that Al serves as the primary diffusion phase between Ti and Al plates. This work may shed light on the development of high-performance anti-penetration multi-layer composites.