Ceramics/metals joining under the influence of electric field: A review

Joining ceramics with ceramics and/or metals is of immense importance to widen the application horizons of ceramics and metals. Solid-state joining is restrained by the high joining temperature and long joining time, both of which can be reduced by liquid-state joining. However, the operating temperature of different ceramic-based components is low because of the low melting temperature of the filler. In order to rapidly join ceramic-based materials at low temperatures, various joining techniques utilizing the effect of an electric field (E-field) have been developed. These methods are generally classified into four categories, i.e., spark plasma sintering joining, low E-field assisted joining, anodic bonding and flash joining, according to the value of applied E-field and the types of materials to be joined, resulting in different joining mechanisms and joint performances. These methods are reviewed from the viewpoint of material types that can be joined and mechanisms.     

Electric field-assisted ion exchange strengthening of borosilicate and soda lime silicate glass

In this study, we investigate the effects of electric field-assisted ion exchange (EF-IE) on potassium for sodium ion exchanges of soda borosilicate and soda lime silicate glasses. The results show that applying an electric field (E-field) with the intensity of 1000 V cm⁻¹ for few minutes produces an exchanged layer with a thickness comparable to the conventional chemical strengthening for 4 hours. There is a critical E-field that increases the mobility and, therefore, the diffusion coefficient of the potassium ions in the glasses. The increase is, perhaps, related to the evolution of the glass structure due to the penetration of potassium ions under an E-field. Vickers indentations showed that strong compression is generated in the glass by EF-IE; however, the bending strength improvement is limited because of the presence of large surface defects and the stress distribution inhomogeneity.     

Phenomenological understanding of flash sintering in MnCo2O4

The dual role of electric field in the flash sintering process of conducting MnCo₂O₄ is demonstrated. The flash and conventionally sintered MnCo₂O₄ samples produced at different temperatures are characterized using energy dispersive X-ray and micro-Raman spectroscopy to elucidate the micro-level spatial distribution of evolved phases. Raman signal mapping over the two ways sintered samples exposes differently grown areas of cobalt oxide based secondary phase. Electrical conductivity of conventionally sintered sample is recorded as a function of temperature and E-field and is utilized to discover the charge carrier activation mechanism during the flash effect. The conductivity before the flash-onset is shown to be comparable to that occurs by Poole-Frenkel effect and Phonon-assisted tunneling i.e. by the mechanism that occurs before the dielectric breakdown of semiconductors and insulators. The observed results, finally, confirm that catalyst like drift action of E-field on cobalt oxide formation is responsible for enhancement in the flash-sintering.     

Fast joining of 8YSZ to NiCrFe medium-entropy alloy by using an electric field

In this study, yttria-stabilized zirconia (8YSZ, 8 mol%) was flash joined to Ni-Cr-Fe medium-entropy alloy (MEA) within seconds under an electric field (E-field), where the current density was above the threshold (about 100 mA·mm⁻²) at 750–1000 °C. The maximum joint strength of 103 MPa was achieved at joining temperature of 900 °C under current density of 100 mA·mm⁻² for 30 s. The impedance spectrum of the joined sample revealed that there was no impedance barrier to charge transfer between the metal electrode and the ceramic, indicating that the interface was well bonded. Scanning electron microscopy and transmission electron microscopy results show that the joint was formed mainly due to the fast diffusion of Ni into 8YSZ and reduced Zr into MEA. The diffusion of these elements does not change the crystal structure of the ceramic and metal, and leads to only slight increase in the lattice spacing of MEA.     

用有机聚合物连接碳化硅陶瓷及陶瓷基复合材料

用陶瓷先驱体有机聚合物连接陶瓷及陶瓷基复合材料是一种成本低廉、工艺新颖、可满足特殊高温条件下连接件要求的新型连接技术。介绍了近年来采用先驱体有机聚合物连接SiC及其复合材料的研究现状，重点对影响连接强度的因素进行分析，并提出相应的改进措施。由于该技术具有连接温度较低、连接过程简单、接头热应力小，连接件的热稳定性高等特点，因此它是陶瓷及其复合材料最有前途的连接方法之一。     

Electrical Joining of Silicon Nitride Ceramics

The electrical joining of sintered Si₃N₄ ceramics by Joule heating was studied. A mixture of CaF₂/kaolinite (70/30 wt%) with excellent electroheating characteristics and reactivity with Si₃N₄ ceramics was selected as a joining agent. The optimum conditions for electrical joining were determined using this joining agent. Analysis of the joint obtained under optimum conditions revealed that joining was accomplished by the formation of reaction zones and a joining layer through the mutual diffusion of the components in the joining agent and the sintering aids in the Si₃N₄. The joint layer was composed of a glassy substance consisting of Ca─Al─Si─Y─O─(F)─(N) and contained a few particles of β─Si₃N₄. Four-point bend tests indicated that joined bodies could be obtained which maintained a strength of about 300 MPa up to 800°C. Finally, a comparative study was made with a joint obtained using furnace heating. These results indicated that the joints obtained using electrical joining were superior to those produced in the furnace.     

Combustion joining of refractory materials

This paper overviews heterogeneous exothermic reactive systems as they apply to the joining of materials. Techniques that are investigated fall under two general schemes: so-called Volume Combustion Synthesis (VCS) and Self-Propagating High-Temperature Synthesis (SHS). Within the VCS scheme, applications that are considered include Reactive Joining (RJ), Reactive Resistance Welding (RRW), and Spark Plasma Sintering (SPS). Under the SHS scheme, Combustion Foil Joining (CFJ) and Conventional SHS (CCJ) are discussed. Analysis of the relevant works show significant potential, particularly for the RJ, RRW, and CFJ approaches, in the joining of a variety of materials which are difficult, or impossible, to bond using conventional techniques. More specifically, it is shown that these methods can be successfully applied to the joining of: (i) dissimilar materials such as ceramics and metals and (ii) refractory materials, such as graphite, carbon-carbon composites, W, Ta, Nb, etc.      

Influence of Joining Interlayer on Impact Damage to Laminated Boron Carbide Ceramics

Impact damage of laminated B₄C ceramic samples was investigated using four types of aluminum sheets — without holes and with 25 4‐, 8‐, and 25‐mm‐diameter holes — at joining ratios of 100, 94, 76, and 45%. Four 1‐mm‐thick B₄C ceramics plates were laminated using three aluminum sheets of the same type and joined at 700°C in vacuum. In impact damage tests using spherical SUJ‐2 projectile with a diameter of 4 mm with a velocity of approximately 300 ms^?1, bulk B₄C showed a large conical crack and significant fractures; the conical crack in the laminated samples was smaller than that of the bulk B₄C. However, the conical cracks of the laminated B₄C with the joining ratio 45 to 96% were of the same size, irrespective of the joining ratios. The total load and induced pressure area on the rear side of laminated samples were smaller than that observed for bulk B₄C, and total load and induced pressure area were similar for laminated samples with high and low joining ratios. The maximum pressure on the rear face of laminated B₄C samples was higher than that observed for bulk B₄C and increased with decreasing joining ratio of laminate interlayer.     

Facile joining of SiC ceramics with screen-printed polycarbosilane without pressure

Joining of SiC ceramics was successfully achieved at a relatively low temperature of 1500 °C without any pressure using pure polycarbosilane (PCS) as the joining material, which was distributed homogenously on the surface of SiC monolith through a screen printing method. The XRD pattern shows that the pyrolysis product of PCS is single-phase SiC. The interlayer thickness of the SiC joint is approximately 2 μm. This ultra-thin interlayer with lower possibility of the existence of defects contributes to the average shear strength of 105.8 ± 10.4 MPa, higher than that of other works using other preceramic polymers to the best of our knowledge. Due to the simplicity, low cost and high joining strength, the screen printing method using PCS as the joining material has good practicality in SiC ceramics joining.     

Ultra-low energy joining: An invisible strong bond at room temperature

We developed Cold Isostatic Joining (CIJ) which is an environmental friendly room temperature joining method. This technique extends cold sintering process to joining of glasses. By optimizing the CIJ conditions a shear stress (18 MPa) comparable to bulk fused silica was achieved. The technique surpasses other joining methods (e.g. adhesive bonding and brazing), because it is insensitive to thermal degradation. Unlike pressure-less silicate bonding, pressure assisted CIJ resulted in a thin joining interlayer (≈27 nm) which maintained its integrity after being heated up to 1000 °C. The in-line transmittance (92%) was identical to un-joined material over the full spectrum making the joining nearly undetectable. The mechanism of CIJ formation and joining were clarified using X-ray diffraction (XRD and pole figure), scanning electron microscopy (SEM) and in line transmittance measurements. The cold joining method could find applications in the field of optics and semiconductors for wafer and lens bonding.     

Joining composite pipes using hybrid prepreg welding and adhesive bonding

A critical technology for composite piping systems in offshore platforms is the joining technique. This paper discusses the development of a hybrid joining approach by using heat‐activated prepreg welding and adhesive bonding. The joining procedure was demonstrated via specimens' fabrication. Four adhesives, with varying mechanical properties, were used to seal the gap between the two pipes. A glass fiber reinforced prepreg was used to wrap the pipes. A total of forty‐five specimens were prepared and evaluated using standardized internal pressure tests. A finite element analysis was conducted to aid in the understanding of the mechanisms of the hybrid joining method. Recommendations for further studies were made based on the test and finite element analysis results.     

Neutron Diffraction and Finite-Element Analysis of Thermal Residual Stresses on Diffusion-Bonded Silicon Carbide-Molybdenum Joints

Various approaches can be used to minimize residual stresses in ceramic-metal joining, such as a refractory-metal interlayer in a hot-pressed joint. Nonetheless, it is still necessary to characterize the stresses at and near the interface between the interlayer and the ceramic, as a function of the hot-pressing parameters. This study combines two techniques to assess the stress distribution of hot-pressed silicon carbide-molybdenum joints: neutron diffraction and finite-element (FEM) analysis. The results demonstrate that the joining temperature greatly influences the final stress distribution, and that significant stress accommodation is achieved by controlling the cooling rate of the diffusion couples. FEM analysis provides a broad view of stress distribution profiles, whereas experimental stress values that are obtained via neutron diffraction allow a better assessment of the effects of parameters that are not easily reproduced using a mathematical model.     

Joining of SiC monoliths using a thin MAX phase tape and the elimination of joining layer by solid-state diffusion

This paper reports the joining of SiC monoliths using a thin MAX phase tape filler, such as Ti₃AlC₂ and Ti₃SiC₂, and the subsequent phenomena leading to the elimination of the joining layer via solid-state diffusion of the MAX phase into the SiC base material, particularly with the decomposition of the Ti₃AlC₂ filler. The base SiC monolith, showing?≥?99% density, was fabricated by hot pressing SiC powder after adding 5?wt. % Al₂O₃-Y₂O₃ sintering additive. A butt-joint configuration was prepared and joined by hot pressing under a pressure of 3.5?MPa. The effects of the experimental parameters, including the type and thickness of the joining filler, temperature as well as the holding time, were examined carefully in terms of the microstructure, phase evolution and joining strength. The joining interface could be eliminated from the SiC base when the SiC monoliths were joined at 1900?°C using a thin Ti₃AlC₂ tape, showing a high joining strength ～300?MPa. Moreover, fracture during the mechanical test occurred mainly at the base material rather than the joining interface, indicating excellent joining properties. These findings highlight the elimination of the joining interlayer, which might be ideal for practical applications because the absence of a joining filler helped preserve the excellent SiC mechanical properties of the joint.     

Modified Tape Casting Method for Ceramic Joining: Application to Joining of Silicon Carbide

A simple modified tape casting procedure has been developed for application to ceramic joining when the joining materials are in powder form. The method involves preparation of a slurry from the powder, solvent, and thermoplastic binder, and then casting directly onto the joining surface using a moving doctor blade. Handling of the tape prior to joining is not necessary: therefore, binder content is minimized, plasticizers are not required, and viscosity is controlled by solvent content. The utility of this technique for producing joints with thin, uniform interlayers is demonstrated for silicon carbide materials joined with TiC + Ni and SiC + Si.     

Effects of the joining process on the microstructure and properties of liquid-phase-sintered SiC-SiC joints formed with Ti foil

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.     

Joining partially-sintered alumina ceramics using a mixture slurry of alumina sol and suspension

The joining of advanced ceramics allows the manufacture of components with a range of complex shapes that cannot be achieved in a cost-effective manner using existing techniques, i.e. green state shaping and/or machining. A new technique for joining partially-sintered alumina ceramics was developed by simply using a mixed slurry of Al₂O₃ sol and suspension. The interlayer of the joints had the same composition as the parent bodies, and the mechanical and chemical properties of the joint were comparable to those of the bulk material. This process can be applied to the joining of a variety of advanced ceramics.     

Monitoring concept for structural integration of PZT-fiber arrays in metal sheets: a numerical and experimental study

ABSTRACT

The technique joining by forming allows the structural integration of piezoceramic fibers into locally microstructured metal sheets without any elastic interlayers. A high-volume production of the joining partners causes in statistical deviations from the nominal dimensions. A numerical simulation on geometric process sensitivity shows that the deviations have a high significant influence on the resulting fiber stresses after the joining by forming operation and demonstrate the necessity of a monitoring concept. On this basis, the electromechanical behavior of piezoceramic array transducers is investigated experimentally before, during and after the joining process. The piezoceramic array transducer consists of an arrangement of five electrical interconnected piezoceramic fibers. The findings show that the impedance spectrum depends on the fiber stresses and can be used for in-process monitoring during the joining process. Based on the impedance values the preload state of the interconnected piezoceramic fibers can be specifically controlled and a fiber overload.     

玻璃与金属连接方法的研究进展

玻璃与金属的异种材料连接技术已广泛应用于精密制造、电子封装、通信遥感和航空航天等领域,进行有关玻璃与金属的连接技术研究具有重要的学术价值和潜在的工程应用价值.简要讲述了玻璃与金属连接时的有关基础问题:界面润湿、界面反应和接头应力.较为全面地介绍了目前研究较多的玻璃与金属之间的连接技术:钎焊、激光焊接、匹配封接、阳极键合和胶接等,并提出未来在大气条件和较低连接温度下实现玻璃与金属连接的可能性.     

Influences of pre-forming on preparation of SiC by microwave heating

Silicon carbide (SiC) crystals were synthesized by microwave sintering using coal and tetraethoxysilane (TEOS) as raw materials. A sol-gel method was carried out to coat coal mineral particles with silicon dioxide (SiO₂). The mixed raw powders were pre-formed by uniaxial pressing into cylindrical pellets in dimension of ~ 30?×?3?mm². The pre-forming pressure was selected at 0?MPa, 1?MPa, 2?MPa, 3?MPa, 4?MPa and 5?MPa respectively, which led to different apparent density of the green pellets. The influence of apparent density of green pellets on microwave heating behavior was investigated. Different microwave thermal effects were analyzed. Techniques of XRD、SEM were carried out to characterize samples. It was found that pre-forming pressure showed crucial influences on microwave thermal effects and electric field (E-field) intensification. No SiC crystal could be formed without pre-forming pressure. Pre-forming pressure might be the prerequisite for synthesis of SiC by microwave heating. Five consecutive and indispensable heating stages including accumulation of residual air, microwave plasma generation, complex chemical reactions, nucleation and grain growth of SiC crystallites could be distinguished for samples under pre-forming pressure. Different pre-forming pressure leads to changes in heating behavior as well as morphologies of SiC crystals. ~ 4?MPa might be the optimized pre-forming pressure for both microwave plasma effects and E-field intensification.     

Almost seamless joining of SiC using an in-situ reaction transition phase of Y3Si2C2

A new design of seamless joining was proposed to join SiC using electric field-assisted sintering technology. A 500 nm Y coating on SiC was used as the initial joining filler to obtain a desired transition phase of Y₃Si₂C₂ layer via the appropriate interface reactions with the SiC matrix. The phase transformation and decomposition of the transition phase of Y₃Si₂C₂ was designed to achieve almost seamless joining of SiC. The decomposition of the joining layer to SiC, followed up by the inter-diffusion and complete densification with the initial SiC matrix, resulted in the formation of an almost seamless joint at the temperature of 1900 °C. The bending strength of the seamless joint was 134.8 ± 2.1 MPa, which was comparable to the strength of the SiC matrix. The proposed design of seamless joining could potentially be applied for joining of SiC-based ceramic matrix composites with RE₃Si₂C₂ as the joining layer.