Ductile Structures Research Articles

Experimental and numerical investigation of the hysteretic behavior of reinforced concrete column-steel beam interior joints under low seismic intensity levels

For the composite frame structure of concrete column and steel beam, a connection structure based on ribbed angle steel connector (RASC) is proposed, and the hysteresis performance and force transmission mechanism of this new type of composite joint are studied. Through quasi-static experimental research, the influence of beam and column cross-sectional dimensions on the bearing capacity, energy dissipation capacity, stiffness degradation, ductility, and failure form of the frame structure was analyzed. The results of experimental and finite element analysis show that the failure forms of this joint under low-cycle repeated loading are mainly manifested as the shear failure of concrete in the core area of beams and columns and sliding failure between angle steel connectors and steel beams, and the hysteresis curves of the joints are similar to those of frame beams and columns, respectively.

Stress-strain behavior of square concrete columns confined with hybrid B-CSM composites and development of novel prediction models

This paper presents a comprehensive investigation into the behavior of concrete confined with hybrid Basalt and Chopped Strand Mat (B-CSM) fibers. The newly proposed B-CSM confinement technique substantially enhances the brittle compressive stress-strain behavior, leading to a noteworthy increase in peak strength (approximately 90%) and ultimate strain (approximately 461 %). The efficiency of B-CSM confinement is affected by the strength of plain concrete, with lower-strength specimens indicating a more pronounced enhancement. The performance of existing analytical models for FRP confinement in predicting ultimate strength and strain in B-CSM confined concrete is assessed, highlighting the need for tailored models. Regression-based equations are proposed for characteristic points along the stress-strain curve, enabling accurate prediction of material behavior. The predicted stress-strain curves exhibit a high level of agreement with experimental results. These findings provide valuable insights for the design and application of B-CSM confinement techniques in structural engineering, facilitating improved performance and ductility of concrete structures under compressive loading conditions.

Experimental investigation of seismic behavior of precast pier‐footing socket connection with different design parameters

AbstractAccelerated bridge construction, with innovative connection details and construction technologies, has been extensively investigated and put into practical application for years. Nowadays, there are three commonly used connection methods of accelerated bridge construction technology, namely, lap‐spliced connection, sleeve connection, and socket connection. Due to the convenience of construction and lower requirements of construction accuracy, the socket connection is more suitable for reconstruction and expansion projects of traffic infrastructure, which could minimize the impact on traffic and accelerate construction progress. According to the structural characteristics of the socket connection, there are some design parameters that may significantly affect the seismic resistance of the structure, such as socket embedment length, fabrication of the shear key, and grouting material strength. To fully study the influence of different design parameters on structural performance, an experiment was carried out to investigate the seismic behavior of the precast pier‐footing socket connections with different design parameters. Five 1:2 scale reinforced concrete precast pier‐footing socket connection specimens with different design parameters were designed and tested under cyclically reversed horizontal loads. The development of hysteresis features, failure mode, load‐bearing capacity, stiffness degradation, structural ductility, energy dissipation capacity, and residual drift are analyzed to reveal the influence of the different design parameters on the seismic behavior of the precast pier‐footing socket connection. The seismic behavior of the precast pier‐footing socket connection was significantly influenced by the embedment length especially when the embedment length was less than 1.0bc. When the embedment length was 0.5bc, the failure mode changed from bending damage at the bottom of the precast pier to the anchorage failure of the precast pier‐footing socket connection. When the embedment length was 1.5bc, the fabrication of the shear key had limited improvement on the seismic performance of the specimen, while reducing the ductility of the specimen. When the embedment length was 1.0bc, the grouting material with a strength grade of C60 could be used in the socket connection between the precast pier and footing. The research presented in this paper provides some design suggestions and a technical basis for evaluating the seismic behavior of precast pier‐footing structures with socket connection.

Influence of the cover plate thickness on the ballistic penetration of re-entrant auxetic structures

This study investigated how mild steel cover plates of various thicknesses affected the collapse of re-entrant auxetic structures under penetration at 500 m/s by ø16 mm spherical projectiles. A combination of experimental and numerical methods was used to capture this effect with auxetic structures made from 3D printed titanium alloy (Ti6Al4V) and ABS plastic (acrylonitrile butadiene styrene), and wire cut 304 stainless steel (SS304). Experimentally, structures were tested with a 2.90 mm cover plate and without the cover plate. Numerically, the effect of the cover plate thickness on the auxetic response of the structure was tested with 0.95 mm, 1.50 mm, and 2.90 mm cover plates (as well as no cover plate). The auxetic densification was found to be greatest under the thickest cover. Material characterisation tests were conducted to develop strength and failure models for the mild steel cover and back plates in this study, which produced simulated correlation to the ballistic experiments. Although the simulated auxetic effect generally increased with cover plate thickness, similar to the experiments, the structure material significantly affected the range of this dependence. For the ductile SS304 structures, a thin (0.95 mm) cover plate showed a small improvement in the auxetic response, with a marked improvement with a 1.50 mm cover plate. Whereas the Ti6Al4V structures showed a steady improvement in auxetic densification as the cover plate thickness was increased. Overall densification of the ABS structures was significantly improved by adding cover plates, however collapse was delayed compared to the other materials. These findings therefore indicate that the thickness of cover plates in auxetic sandwiches can be specifically engineered to maximise auxetic effect while considering the ranges of this dependence with different auxetic materials.

Material Characterizations of the Polymers Reinforced with Recycled Flexible Plastic Blends as Filament for 3D Printing

The high consumption of single-use plastics and the low recycling rates have seriously polluted the soil and ocean environments. Thermoplastic materials from recycling can be used to make filaments for 3D printing. This study is focused on preparing, characterizing, and comparing the polymers reinforced with recycled flexible plastic blends to be used as a filament in additive manufacturing. In this regard, two types of polymers were used to create the filament: High-Density Polyethylene (HDPE) and Polypropylene (PP), which were mixed with recycled flexible plastic (RF). The mixture was initially used to create filament by using a single extrusion machine, with various ratios of virgin HDPE and PP to recycled flexible plastic (in weight%) at temperatures of 190°C and 230°C. Then, the filament blends were characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM). TGA analyses revealed that RF can increase the thermal stability of V- HDPE and V-PP upon blending, and HDPE/RF blends show a higher decomposition temperature than PP/RF. FESEM indicated that adding 30% RF is the best percentage for both polymer blends where the structure appears ductile. It can be concluded that the HDPE 70% blend is suitable for 3D printer filament as it showed the best decomposition temperature and the ductility of the fracture structure, which meet the requirements for 3D printer filament.

Seismic Performance and Damage Evaluation of Reinforced Concrete Structures Based on Field Investigation Made After February 6, 2023, Kahramanmaraş Earthquakes

On 6 February 2023, an earthquake doublet occurred, the first at Kahramanmaraş Pazarcık district ([Formula: see text]) at local time 04:17 and the second, which approximately 9 hours after the first earthquake, occurred at Kahramanmaraş Elbistan district ([Formula: see text]) at local time 13:24 in Türkiye. It is a disaster affected 11 cities in the eastern region in Türkiye and is referred as “Disaster of the Century”. Earthquake disasters allow humanity to investigate seismic behavior under related construction details and revising the seismic codes. The authors conducted observational research to obtain interpretive information and digital data by investigating structural damages of moderately and heavily damaged buildings from earthquake sites. In this paper, performance evaluation is done based on existence of soft storey, weak column-strong beam, deficiencies and pounding effect. Damages are classified as beam, column, beam-column joint and shear wall, infill wall, roof and scaffolding damages. Ampleness of soft storey, column damages, inadequate joint reinforcement, inadequate structural ductility and low capacity, strong beam-weak column effect, and infill wall damages have been observed from the field. As a result of field observation, structural deficiencies, irregularities and mismatching capacity design principles have been concluded as common problems of reinforced concrete buildings in the Kahramanmaraş earthquake site.

Regression algorithms-driven mechanical properties prediction of angle bracket connection on cross-laminated timber structures

The construction of structures using cross-laminated timber (CLT) has grown in popularity as a result of its environmentally friendly and high-strength characteristics. The primary function of angle bracket connections is to resist the force of CLT structures under horizontal forces, which is essential to ensure the seismic resilience and ductility of CLT structures. A regression algorithms-driven method for predicting the mechanical performance of angle bracket connections is introduced in this study. As input parameters, the geometric dimensions of the angle bracket connector, the connection method of the connector with the wall and floor slabs, and the properties of the CLT panel are utilized to predict the yield load, the maximal load, the initial stiffness, and the ductility ratio of the angle bracket connection. Prediction models were developed using the collected data from 110 angle bracket experiments, and each prediction model's performance was discussed in depth. Lastly, the permutation importance and SHapley Additive exPlanations (SHAP) value analysis were used to interpret the prediction models. The results showed that the extreme gradient boosting (XGB) algorithm could accurately predict the maximum and yielding load of the angle bracket connection, with R2 reaching 0.968 and 0.939. Furthermore, in predicting the initial stiffness of the angle bracket, the XGB algorithm performed the best with an average ratio of predicted to actual values of 0.985. The results indicated that this study proposed an accurate and efficient method for angle bracket connection to predicting its mechanical properties and confirmed the trustworthiness and feasibility of the prediction models.

Influence of the ground motion directionality on the global ductility of 3D RC structures

This study examines the influence of ground motion directionality on global ductility μ_s of framed reinforced concrete structures. Suitable values of angle of attack θ, longitudinal reinforcement ratio ρ_l, dimensionless axial stress υ and mechanical ratio of transverse reinforcement ω_wd were assumed. Detailed nonlinear modeling was adopted to reproduce the behavior of reinforced concrete elements in the plastic field considering, also, the confinement effect on concrete mechanical properties. Nonlinear static simulations were carried out with the capabilities of the OpenSees code to evaluate the capacity curves and the corresponding global ductility. The results show that plastic hinges develop on the columns for the combined effect of bending moments transmitted by the beams framing into the same joint for values of the angle θ equal to 30° and 45°. Consequently, the formation of soft-storey mechanisms significantly reduces the global ductility μ_s. A design formula is proposed to avoid such collapse mechanism for framed reinforced concrete structures in ductility class high

Structural performance of the concrete-filled tube column with internal triangular units subjected to axial compression.

This study introduces a novel concrete-filled tube (CFT) column system featuring a steel tube comprised of four internal triangular units. The incorporation of these internal triangular units serves to reduce the width-thickness ratio of the steel tube and augment the effective confinement area of the infilled concrete. This design enhancement is anticipated to result in improved structural strength and ductility, contributing to enhanced overall performance and sustainability. To assess the effectiveness of the newly proposed column system, a full-scale test was conducted on five square steel tube column specimens subjected to axial compression. Among these specimens, two adhered to the conventional steel tube column design, while the remaining three featured the new CFT columns with internal triangular units. The shape of the CFT column, the presence of infilled concrete and the presence of openings on the ITUs were considered as test parameters. The test results reveal that the ductility of the newly proposed CFT column system exhibited a minimum 30% improvement compared to the conventional CFT column. In addition, the initial stiffness and axial compressive strength of the new system were found to be comparable to those of the conventional CFT column.

First-principles investigations of Fe-based A3BX ceramics with high stiffness and damage tolerance.

In the search for high-stiffness and damage-tolerant materials, Fe-based A3BX carbide and nitride anti-perovskites were studied using first-principles calculations. These perovskites were found to be stable in cubic structures, as substantiated by the formation energy, elastic Born stability criterion, and phonon dispersion spectrum analysis. The GGA functional was applied for geometry optimization, and the lattice constants are found to be 3.730 Å, 3.715 Å, 3.832 Å, and 3.828 Å for Fe3AlC, Fe3AlN, Fe3SnC, and Fe3SnN, respectively. Elastic property analysis reveals that all the materials have large elastic moduli, high sound velocities, and high Debye temperatures. Among them, carbides have superior stiffness and quasi-ductile properties, and they can be further improved by applying additional pressure. Preliminary analysis of electronic properties indicates that they are ferromagnetic and metallic compounds. Their high melting temperatures (>2600 K) confirm their potential in high-temperature applications. The lowest thermal conductivity of Fe3SnN suggests its potential in efficient solid-state refrigeration application. Moreover, Fe3SnC is proposed to be a viable damage-tolerant material with good prospects. Under 10 GPa external pressure, it possesses a ductile structure with a Young's modulus of 402.15 GPa and bulk modulus of 280.25 GPa.

Seismic performance of confined prestressed hollow core wall panels part II: Numerical simulation and analysis

In Part I of this research, confined prestressed hollow core wall structures were proposed and experimental tests of 19 specimens were conducted to study its mechanical behaviors. In this part, a detailed finite element model was developed in ANSYS to provide a tool for further investigating the seismic behaviors of confined prestressed hollow core wall structures. Contact elements were applied to simulate the interaction between material interfaces. Techniques in ANSYS including coupling of degrees of freedom (CP) of overlapped nodes and deactivation of concrete elements (EKILL) were adopted, along with restart analysis (REST) to simulate nonlinear mechanical behaviors of the structural system. The developed modeling method was verified by the experimental test results and was shown to accurately predict the global and local behaviors such as failure modes and load bearing capacities of precast hollow core walls. Parametric analysis on shear span ratio, axial load ratio, rigidity of floor systems as well as strength of vertical wall-wall joints was conducted, and relevant design recommendations were provided for prestressed hollow core wall structures. Results show that for a ductile prestressed hollow core wall structure, the axial load ratio is recommended to be smaller than 0.06 and the story number less than 5. Influence of rigidity of floor systems requires further study with dynamic tests, but low-strength vertical wall-wall joint is highly recommended for this system. Two analytical mechanisms that are shear-flexural mechanism and truss mechanism were proposed for calculation of load bearing capacities. These two mechanisms provide good predictions for an upper bound and a lower bound for load bearing capacities of prestressed hollow core walls, respectively. From Part I and II of this research, the mechanical behaviors of prestressed hollow core wall structures are verified experimentally, numerically, and theoretically, and it is concluded that they can be used as a potential choice for low-rise buildings in rural areas.

Virtual modelling aided safety assessment for ductile structures against high-velocity impact

This paper introduces a virtual modelling-aided computational analysis framework for assessing the safety of a ductile engineering object against high-velocity impact. By evaluating the data feedback continuously collected from the working site, the presented Virtual Modelling Aided Safety Assessment (VMASA) scheme is competent to effectively report the current safety level of the engineering object. The safety level (alternatively known as the reliability), of the impacted system can be quantified by using the first-passage theory. By considering various mercurial factors that are influencing the high-velocity impact for ductile materials, in this research, a new machine learning-aided virtual modelling technique as the clustering extended support vector regression (CXSVR), is implemented to evaluate the capacity of the engineering product against different conditions. Also, the John-Cook failure model is transformed into a random format to simulate the dynamic response of the engineering product against high-velocity impacts. A new T-spline kernel has also been developed within the CXSVR scheme. By using the VMASA, the inherent limit state function can be quantitatively certified by analysing the relationship between the system inputs and outputs. Both experimental and numerical investigations are implemented to demonstrate the accuracy, practicability, and efficiency of the proposed safety assessment framework.

Structural size effect in the mode I and mixed mode I/II fracture of strain-hardening cementitious composites (SHCC)

The size effect in the fracture of solids represents a highly critical issue with a prolonged history of research. The size effect of traditional quasi-brittle materials can already be well described through the size effect model. However, there is still a lack of research on the size effect of strain-hardening cementitious composites (SHCC), a special type of fibre-reinforced concrete with macro-scale strain-hardening behaviour after first cracking. Being distinct from traditional quasi-brittle materials with softening nature, SHCC is thus expected to behave differently in terms of size effect. In this research, the structural size effect problem of SHCC is comprehensively studied by experimental investigation and theoretical analysis. Geometrically similar notched three-point bending specimens were tested in mode I and mixed mode I/II fracture condition. The whole-process of failure and matrix cracking zone around the main crack was captured with high resolution by digital image correlation technology. Experimental results showed that apparent fracture energy, nominal strength, structural ductility and fracture resistance curve are all structural size-dependent. The apparent fracture energy was shown to arise with specimen size within the tested range. This is related to large-scale pseudo yielding, i.e., enlargement of matrix cracking zone (like the yielding zone in metals) with increasing structural size. It thus provides an indirect method for the estimation of cohesive fracture energy of single crack with constitutive nature. Due to the scaled matrix cracking zone, an intermediate asymptote exists in the size effect curve of nominal strength, in addition to the plastic and LEFM asymptotes in the Bažant original size effect law. This resembles the recent finding of intermediate asymptote in plastic-hardening metal. The size-dependence of R-curve was also examined. Though size-dependent, the equivalent LEFM-based R-curves are shown to have three common stages reflecting different cracking processes. Based on experimental results, the size effect of fracture energy and nominal strength are finally modelled theoretically in the Bažant’s framework of equivalence between energy release and fracture resistance.

Mechanical behaviour of ductile polymer cellular model structures manufactured by FDM

In this work, Acrylonitrile-Butadiene-Styrene model structures were manufactured by FDM, and their mechanical behaviour investigated under compression, both at small and at large strains. The structure design strategy adopted, based on the use of circular cross-section beam-like elements formed under controlled conditions, led to obtain open-cell structures (with a porosity degree of ≈ 65%) composed of unit cells with different shapes and dimensions assembled to form regularly repeating patterns. The stress-strain behaviour, from cube- and prism-shaped specimens with different sizes and loaded along different directions, was discussed in the light of the outcomes from (i) cyclic compression experiments and (ii) morphological analyses of cryogenic fracture surfaces of specimens compressed at high strain levels. The response along the 3D-stacking direction was traced back to the elastic-plastic case, with non-recoverable strain starting to accumulate between 3% and 5% strain and structure densification starting below 20%. The specimen size effects turned out to be little pronounced. Slightly higher levels of stiffness and strength were measured for the largest cube. This result was discussed on the basis of the peculiar morphology of the structure examined.

Retrogression of ultrahigh-pressure eclogite, Western Gneiss Region, Norway

Abstract. The Western Gneiss Region (WGR) in western Norway exposes ultrahigh-pressure (UHP) eclogites that occur repeatedly, within an area of high-pressure (HP) eclogites, without evidence of being separated by tectonic shear or ductile flow structures. We studied 10 eclogites from two northern UHP areas and the interjacent HP area to evaluate the significance of this pattern. The orthopyroxene in orthopyroxene-bearing samples has low Al2O3 contents (0.17 wt %–0.37 wt %), provided its grain boundaries were unaffected by partial recrystallisation or replacement. Classical geothermobarometry based on element partitioning between coexisting mineral phases suggests metamorphic conditions within the diamond stability field for the samples from both the HP and UHP areas. The primary clinopyroxene in the associated orthopyroxene-free eclogites contains aligned inclusions of either needle-shaped quartz ± pargasite or lamellar albite, which are absent from the secondary (symplectic) clinopyroxene. Reconstructed mineral compositions of the primary clinopyroxene obtained from grain cross-section surfaces using a scanning electron beam or image processing are non-stoichiometric, and they have higher Ca-Eskola and lower Ca-Tschermak components than the inclusion-bearing host clinopyroxene. The molar ratios of these endmembers are consistent with the needles in the primary clinopyroxene being formed from vacancy-bearing precursor clinopyroxene by the exsolution reaction 2 Ca-Eskola = Ca-Tschermak + 3 quartz during early eclogite-facies retrogression. Further retrogression partially transformed the needle-shaped quartz to irregularly shaped albite within the clinopyroxene and partially transformed both clinopyroxene generations to amphibole that occasionally preserves the needles. The similarity of both the maximum metamorphic conditions and the mineral exsolution microstructures in the eclogites from UHP and HP areas indicates a shared metamorphic history within the stability field of diamond, but a history that diverged during retrogression. Consequently, the alternations of UHP and HP areas in the WGR may have formed by a process that allowed for spatial variations in retrogression efficiency, such as the localisation of strain (recrystallisation) or fluid flow (diffusion) or both, rather than by tectonic stacking of UHP and HP units. Evidence for the UHP metamorphism of WGR crustal rocks is now found from NE to SW along the entire coastal section that covers previously recognised UHP and interjacent areas.

Investigation of Ductile Point-Contact Yield Strength and Bilinear Reinforced Elastic–Plastic Mechanical Behavior Model

Ductile point-contact structures are widely used in engineering applications, with their yield strength and mechanical behavior directly related to the application safety of relevant engineering structures. The Hertz elastic contact theory can effectively express the mechanical behavior of a point-contact structure at the initial stage of load bearing. However, it cannot be applied when the structure has a characteristic yield. In this study, by analyzing the stress distribution characteristics of a point-contact structure prior to characteristic yield, the maximum contact stress on the contact surface was numerically calculated and summarized. Based on the assumption of simplified bilinear constitutive relation of materials, an elastic–plastic analytical model was derived to characterise the mechanical behavior of ductile point-contact structures before and after yield, with its validity verified using the finite element numerical calculations and experimental method.

Deep Learning-Based Automatic Defect Detection of Additive Manufactured Stainless Steel

Accumulating interest from academia and industry, the part of quality assurance in metal additive manufacturing (AM) is achieving incremental recognition owing to its distinct advantages over conventional manufacturing methods. In this paper, we introduced a convolutional neural network, YOLOv8 approach toward robust metallographic image quality inspection. Metallographic images accommodate key information relating to metal properties, such as structural strength, ductility, toughness, and defects, which are employed to select suitable materials for multiple engineering execution. Therefore, by comprehending the microstructures, one can understand insights into the behavior of a metal component and make predictive assessments of failure under specific conditions. Deep learning-based image segmentation is a robust technique for the detection of microstructural defects like cracks, inclusion, and gas porosity. Therefore, we improvise the YOLOv8 with dilated convolution mechanisms to acquire automatic micro-structure defect characterization. More specifically, for the first time, the YOLOv8 algorithm was proposed in the metallography dataset from additive manufacturing of steels (Metal DAM) to identify defects like cracks and porosity as a novel approach. A total of 414 images from ArcelorMittal engineers were used as an open-access database. The experimental results demonstrated that the YOLOv8 model successfully detected and identified cracks and porosity in the metal AM dataset, achieving an improved defect detection accuracy of up to 96% within just 0.5 h compared to previous automatic defect recognition processes.

Few‐Hydrogen Metal‐Bonded Perovskite Superconductor MgHCu3 with a Critical Temperature of 42 K under Atmospheric Pressure

AbstractSince the prediction of multi‐hydrogen high‐temperature superconductor by Ashcroft in 2004, many possible candidates have been proposed, e.g., LaH10 showing the highest superconducting transition temperature (Tc) around 250–260 K at 170‐200 GPa hitherto. However, this pressure is too large to be taken into practical use. To address this challenge, it proposes a few‐hydrogen metal‐bonded perovskite superconductor, MgHCu3, by combining a novel design idea with first‐principles calculations. Different from multi‐hydrogen hydrides, whose high Tc relies on extreme pressure, the metallic bond in few‐hydrogen superconductor MgHCu3 improves the structural stability and ductility at atmospheric pressure. Here, the small amount of hydrogen is found to be vital for Tc. After the incorporation of hydrogen, the electron–phonon coupling constant of MgHCu3 is increased to 0.83, which is larger than that of the well‐known MgB2. Moreover, the anisotropy of MgHCu3 also plays an important role in enhancing Tc. Based on the Migdal‐Eliashberg theory, it predicts that the phonon‐mediated metal‐bonded perovskite MgHCu3 is a superconductor with Tc of 42 K. The first predicted ternary metal‐bonded perovskite, MgHCu3, enriches the family of perovskite and will promote further investigation on few‐hydrogen superconductors under atmospheric pressure.

Multifunctional Polymer-Metal Lattice Composites via Hybrid Additive Manufacturing Technology.

With increasing interest in the rapid development of lattice structures, hybrid additive manufacturing (HAM) technology has become a competent alternative to traditional solutions such as water jet cutting and investment casting. Herein, a HAM technology that combines vat photopolymerization (VPP) and electroless/electroplating processes is developed for the fabrication of multifunctional polymer-metal lattice composites. A VPP 3D printing process is used to deliver complex lattice frameworks, and afterward, electroless plating is employed to deposit a thin layer of nickel-phosphorus (Ni-P) conductive seed layer. With the subsequent electroplating process, the thickness of the copper layer can reach 40 μm within 1 h and the resistivity is around 1.9×10-8 Ω⋅m, which is quite close to pure copper (1.7 ×10-8 Ω⋅m). The thick metal shell can largely enhance the mechanical performance of lattice structures, including structural strength, ductility, and stiffness, and meanwhile provide current supply capability for electrical applications. With this technology, the frame arms of unmanned aerial vehicles (UAV) are developed to demonstrate the application potential of this HAM technology for fabricating multifunctional polymer-metal lattice composites.

High-density dislocation and ductile precipitate synergistically reinforced TiAl/Ni-based superalloy joint using novel multi-principal element interlayer

An extremely high-strength TiAl/Ni-based superalloy dissimilar joint was obtained using a designed Ni25Zr25Sn20Cu10Hf10Cr5Fe5 multi-principal element interlayer via contact reaction brazing. It was found that a joint mainly composed of eutectic structure of (Ni)ss, (Ni, Cr, Fe)ss, and (Cr, Ni, Fe, Mo)ss, as well as micro-nano precipitates of (Ti)ss and (Hf, Zr)ss, could be achieved through the interaction between the interlayer and the base metals. The joint exhibited a shear strength of 498 MPa when brazed at 1190 °C for 10 min, while the fracture occurred within the TiAl base metal, and the retention rate of high-temperature (HT) strength (650 °C) was ∼100%. The strengthening mechanism of the brazed joint was systematically discussed by transmission electron microscopy (TEM). It was shown that high-density dislocations existed in each phase of the seam as well as twinning and stacking faults existed in the micro-nano precipitates, caused by a mass of solute atoms, greatly strengthened the joint. At HTs, the dislocation strengthening effect weakened due to grain recovery and recrystallization, but the joint could be additionally toughened by multi-cracking. Meanwhile, granular (Ti)ss dispersed through the seam and ductile reticular structure (Ni)ss toughened the joint via the mechanism of crack termination and bridging. The proposed method provides a new approach for high strength and heat resistance joining of TiAl/Ni-based superalloy in aeroengine components.