Advanced high-temperature (RT-1100°C) resistant adhesion technique for joining dissimilar ZrO2 ceramic and TC4 superalloys based on an inorganic/organic hybrid adhesive

To meet the high demand for ceramic/superalloy composite structural components in various fields, an advanced high-temperature adhesion technique was firstly developed by preparing a novel inorganic/organic hybrid adhesive suitable for ZrO₂ and TC4. Chemical bonding started to work at ～600°C, and became the crucial bonding mechanism at elevated temperatures. The formation of ZrSiO₄ and Ti₅Si₃ at the interfaces of two substrates not only increased the interfacial connection strength, but also formed two gradient layers with a size of ～2 μm to effectively alleviate the difference of composition and performance between the adhesive and substrates. In the temperature range of 500–900°C, the matching degree of CTE among ZrO₂, adhesive and TC4 is higher, and the maximum difference does not exceed 3×10^-6 K^-1. Meanwhile, the formation of a composite structure containing various ceramics (ZrO₂, SiC and ZrB₂) and intermetallics (Ni–Si, Al–Ni), and the improvement of structural compactness of adhesive from 500 to 900°C greatly improved the bonding strength to the maximum value of 31.4 MPa at 900°C. Also, the adhesive pretreated at 900°C showed good thermal cycling resistance, and the strength was still higher than 15 MPa after 50 cycles. For cured adhesive, when used directly in an extreme environment, it can provide bonding strength not less than 5 MPa in the whole temperature range, indicating that the adhesive possessed potential emergency repair convenience. This work significantly broadened the application of high-temperature-resistant adhesion technology in the connection of dissimilar ceramics and alloys.     

DC-driven ultrafast transient liquid phase bonding of 3YSZ and GH3128 superalloy using Ni interlayer

A direct current (DC)-driven transient liquid phase bonding strategy was proposed for joining 3 mol% Y₂O₃-stabilized ZrO₂ (3YSZ) and GH3128 superalloy with a Ni interlayer. The DC application triggered the rapid formation and diffusion of metallic Zr in 3YSZ and chemical reactions at the 3YSZ/Ni interface. The formed Ni–Zr eutectic liquid well wetted 3YSZ and hence completely filled the bonding gap in seconds. Eutectic structures in the joints were eventually transformed into Ni–Zr intermetallic compounds or a Ni-based solid solution. The remaining Ni interlayer effectively alleviated residual stress through plastic deformation during cooling stage, and thereby contributed substantially to the high joint strength. Under the joining conditions of a current density of 30 mA/mm², an energization time of 30 s, and a joining temperature of 1100°C, the obtained joints exhibited a maximum shear strength of 188 ± 8 MPa. This paper proposes an economical and reliable method for the rapid preparation of YSZ/metal joints for high-temperature applications.     

Advanced high-temperature resistant (RT-1000 °C) aluminum phosphate-based adhesive for titanium superalloys in extreme environments

To facilitate the repairing and connecting processes for titanium superalloys, an advanced high-temperature resistant adhesive that can be converted to a composite of intermetallics and ceramics was prepared by modifying aluminum phosphate-based adhesive with various additives. The composition evolution of the adhesive, the structure changes in the bonding layer, the reaction process at interfaces and the fracture mode of joints are comprehensively studied to explore the bonding mechanism. The results showed that the chemical bonding based on the formation of TiSi and Ti₅Si₄ started to work at 600 °C, and became the crucial bonding mechanism at higher temperatures. A diffusion reaction layer with size up to 6 μm effectively alleviated the difference of composition and performance between alloy substrate and adhesive. From RT to 900 °C, the coefficient of thermal expansion (CTE) of adhesive matched well with that of alloy substrates, and the difference of their CTE was always lower than 2 × 10⁻⁶ k⁻¹. The bonding strength reached ~16 MPa after pre-treatment at 900 °C without pressure, and remained over 13 MPa within the common operating temperature range (400–600 °C) of TC4 alloys. Without any pre-treatment, the adhesive could still provide above 5 MPa in range of RT-600 °C.     

Preparation of high-temperature organic adhesives and their performance for joining SiC ceramic

Two kinds of high-temperature organic adhesives were prepared and successfully applied to join SiC ceramic. One adhesive was composed of preceramic polymer (V-PMS) and B₄C powder (HTA-1), and the other was composed of V-PMS, B₄C powder and low melting point glass powder (HTA-2). The properties of the obtained adhesives were investigated by TGA, XRD, bonding test and SEM analysis. The results show that the obtained adhesives exhibit outstanding heat-resistant property and excellent bonding strength. The bonding strength of HTA-1 treated at 200 °C, 400 °C, 600 °C were 26.8 MPa, 18.9 MPa, 7.3 MPa, respectively. When the temperature increased to 800 °C or even higher, the shear strengths of the joints were enhanced to over 50 MPa. Moreover, by adding glass powder as the second filler, it was found that the minimum shear strength of HTA-2 was enhanced to 16.4 MPa. The excellent performances of the obtained adhesives make them as promising candidates for joining SiC ceramics for high-temperature applications.     

Nano-infiltration and transient eutectic (NITE) joining of SiC ceramics applied for the harsh environments

To expand the application of SiC/SiC joints under extreme conditions, Nano-Infiltration and Transient Eutectic (NITE) joining technology with AlN-Y₂O₃ as a sintering additive was successfully developed. The rheological properties of the slurry and the microstructure evolution of the joints were systematically characterized by rheometer, SEM, EDS, EBSD, and TEM, respectively. Both room-temperature and high-temperature flexural strength was measured to evaluate the mechanical properties of the joints. An immersion test with concentrated nitric acids was performed to evaluate the corrosion resistance of the joints. The defect-free joining layer was composed of a dense α-SiC phase, a small amount of YAG(Y₃Al₅O₁₂) distributed in the triangular grain boundary, and a Y-Al-O glass phase from AlN-Y₂O₃. The mechanism of NITE joining could be attributed to the incoherent growth of the newly generated α-SiC in the joining layer along the α-SiC substrate. The maximum room-temperature strength of the joints was 320.5 ± 37.6 MPa. When the test temperatures were 1000 °C, 1200 °C, and 1400 °C, the flexural strength reached 238.7 ± 33.1 MPa, 215.5 ± 52.5 MPa, and 166.9 ± 52.0 MPa, respectively. After immersing the joints in a concentrated HNO₃ for 168 h, the flexural strength was 173.3 ± 12.6 MPa. The joints' excellent mechanical properties and corrosion resistance reveal great application potential under extreme conditions.     

Microstructure and mechanical property of SiC whisker coating modified C/C composite/Ti2AlNb alloy dissimilar joints prepared by transient liquid phase diffusion bonding

SiC whisker coating was prepared on the surface of C/C composite successfully by CVD, and transient liquid phase (TLP) diffusion bonding was employed to realize the joining of SiC whisker coating modified C/C composite and Ti₂AlNb alloy using Ti–Ni–Nb foils as interlayer. The microstructure, shear strength and fracture behavior were investigated by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and universal testing machine. The results show that SiC has good compatibility with C/C composite, and gradient interface formed between SiC-modified C/C composite and Ti₂AlNb alloy. When the bonding experiment was carried out under bonding temperature of 1040 °C and holding time of 30min with 5 MPa pressure in vacuum, the joints formed well and no obvious defects can be observed. The typical microstructure of joints is C/C composite/SiC + TiC/Ti–Ni compounds + Ti–Ni–Nb solid solutions/residual Nb/diffusion reaction layer/Ti₂AlNb alloy. With the increasing of bonding temperature, the thickness of joining area increased due to sufficient element diffusion. However, when bonding temperature is elevated to 1060 °C, some defects such as cracks and slag inclusions exist in the interface layer between interlayer and Ti₂AlNb. The joints with maximum average shear strength of 32.06 MPa are bonded at 1040 °C for 30min. C, SiC and TiC can be found on the fracture surface of joints bonded at 1040 °C which indicated that fracture occurred at the interface layer adjacent SiC layer.     

Preparation of a modified phosphate-based adhesive and its hot bonding performance on 316L stainless steel

In this study, a novel phosphate-based adhesive was prepared by using homemade aluminum phosphate as a matrix and by adding different fillers simultaneously. The effects of calcination temperature and filler composition on the bonding mechanism and high-temperature bonding strength of the adhesive for high-temperature alloys were studied. The results indicated that the crystalline transformation of AlPO₄ occurred at 500 °C. AlPO₄ has two crystalline forms at 500 °C: orthorhombic and hexagonal. The addition of CuO to the fillers resulted in the exchange of Fe and Cu at the substrate interface and enhanced the high-temperature bonding strength of the specimens. The maximum tensile strength of the specimens reached 3.9 MPa at 500 °C. These composites have potential applications in aviation, aerospace, and other fields.     

Room-temperature direct bonding of ZrO2 ceramic and SiCP/Al composite using ultrasonic waves

Direct bonding of ZrO₂ ceramic and SiC_P/2A14 composite was successfully achieved in only a few seconds using ultrasonic waves at room temperature. A continuous void-free amorphous Al₂O₃ interphase layer with an average thickness ranging from 60 to 70 nm was verified to be formed between ZrO₂ ceramic and SiC_P/2A14 composite, which could be attributed to the significantly enhanced diffusion of O and Al atoms around the bonding interface due to a remarkable increase in defect density caused by the physical effects of ultrasonic vibration. The maximum average shear strength of the ZrO₂–SiC_P/2A14 joints was approximately 36.48 MPa.     

Properties of TiB2–PSO modified SiHfBCN-based adhesive through polymer-derived-ceramic route

High temperature SiHfBCN-based ceramic adhesives are fabricated by polymer derived ceramic route with SiHfBCN precursors, TiB₂ and polysiloxane (PSO). The phase composition and microstructure were investigated by X-ray diffraction and scanning electron microscopy, respectively and the evolution of pores was analyzed by Micron X-ray 3D Imaging System and VG Studio MAX 3.0.2 software. After heat-treating at 80 °C and curing at 170 °C in air, the adhesion strength detected in air of SiHfBCN adhesives is 3.22 MPa at room temperature (RT) and can rise to 5.47 MPa at 1000 °C after pyrolysis at 1000 °C in air for 2 h with a universal testing machine. By modifying SiHfBCN with TiB₂–PSO, the adhesion strength can be enhanced to 9.49 MPa at RT and 6.37 MPa at 1000 °C. The results indicate that the formation of SiO₂–B₂O₃–TiO₂ ternary glasses play an important role in improving the adhesion strength. The present study broaden the high temperature adhesive family suitable for large-scale complex ceramic components in harsh environments.     

Influence of ZrO2 Content on the Performances of BN‐ZrO2‐SiC Composites for Application in the Steel Industry

BN‐ZrO₂‐SiC composites were fabricated with different ZrO₂ contents ranging from 0 to 40 vol%. The mechanical properties and corrosion resistance against molten steel increase with increasing ZrO₂ content, while thermal shock resistance decreases gradually. When ZrO₂ content is 40 vol%, the flexural strength is 346 MPa and corrosion depth is 254 μm. The improved corrosion resistance is attributed that the corrosion layer formed by residual ZrO₂ hinders molten steel penetration. Nevertheless, composite with 40 vol% ZrO₂ shows a sharp decline in residual flexural strength when temperature difference is more than 400°C and critical temperature difference is 520°C.     

Low-temperature joining of SiC ceramics using NITE phase with Al2O3-Ho2O3 additive

In order to avoid the property degradation resulting from high-temperature joining process, nano-infiltrated transient eutectoid (NITE) phase with the Al₂O₃-Ho₂O₃ as the joining adhesives was adopted to join silicon carbide (SiC) ceramics with the attempts to lower down the joining temperature. The liquid-phase-sintered silicon carbide (LPS-SiC) specimens were joined at 1500-1800°C by spark plasma sintering (SPS) under the pressure of 20 MPa. The results of the shear test and microstructure observation showed that the joining process could be finished at a relatively lower temperature (1700°C) compared to other NITE-phase joining. In contrast to the shear strength of 186.4 MPa derived from the SiC substrate, the joint exhibited the shear strength of 157.8 MPa with the fully densified interlayer.     

Process optimization of solvent based polybenzimidazole adhesive for aerospace applications

The use of adhesive bonding for high temperature applications is becoming more challenging because of low thermal and mechanical properties of commercially available adhesives. However, the development of high performance polymers can overcome the problem of using adhesive bonding at high temperature. Polybenzimidazole (PBI) is one such recently emerged high performance polymer with excellent thermal and mechanical properties. It has a tensile strength of 160 MPa and a glass transition of 425 °C. Currently, PBI is available in solution form with only 26% concentration in Dimethyl-acetamide solvent. Due to high solvent contents, the process optimization required lot of efforts to form PBI adhesive bonded joints with considerable lap shear strength. Therefore, in present work, efforts are devoted to optimize the adhesive bonding process of PBI in order to make its application possible as an adhesive for high temperature applications. Bonding process was optimized using different curing time and temperatures. Epoxy based carbon fiber composite bonded joints were successfully formed with single lap shear strength of 21 Mpa. PBI adhesive bonded joints were also formed after performing the atmospheric pressure plasma treatment of composite substrate. Plasma treatment has further improved the lap shear strength of bonded joints from 21 MPa to 30 MPa. Atmospheric pressure plasma treatment has also changed the mode of failure of composite bonded joints.     

Synthesis of a novel preceramic polymer (V-PMS) and its performance in heat-resistant organic adhesives for joining SiC ceramic

Heat-resistant organic adhesives are urgently needed for aeronautical and astronautical applications, and there have been only a few successful studies in this field. In this work, a novel preceramic polymer (V-PMS) has been synthesized by modifying polymethylsilane with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, [CH₃(CH₂CH)SiO]₄, and this has been used as a heat-resistant adhesive. The obtained adhesive was found to exhibit outstanding thermal and bonding properties. The ceramic yield was about 81% (in Ar) and 90.6% (in air) at 1200 °C. The shear strength was 14.9 MPa at room temperature, and this increased to a maximum of 31.7 MPa after treatment at 1000 °C for 2 h in air. Moreover, it was interesting to find that on addition of B₄C powder to the preceramic polymer, its shear strength was surprisingly enhanced up to 50.8 MPa after annealing at 1200 °C under air atmosphere. Their excellent performances make the obtained adhesives promising candidates for joining SiC ceramics in high-temperature applications.     

Preparation and mechanical properties of the 2.5D ASf/ZrO2 composites after high-temperature heat treatment

In the paper, the aluminosilicate fiber-reinforced zirconia (AS_f/ZrO₂) ceramic composites were successfully fabricated by polymer impregnation and pyrolysis (PIP) method. The microstructure and high-temperature mechanical properties of the original composites were well studied. The results revealed that the composites could maintain the stability of microstructure at 1000 °C. The flexural strength increased from 58.82 ± 2.83 MPa to 88.74 ± 6.20 MPa and the flexural modulus increased from 29.26 ± 4.67 GPa to 40.76 ± 8.76 GPa. The thermal exposure improved the interfacial bonding and made the load transfer more effective. After heat treatment from 1200 °C to 1400 °C, the flexural strength gradually declined due to the crystallization of the AS fibers and ZrO₂ matrix, while the flexural modulus increased in a completely different trend. After heat treatment at 1400 °C, the composites could maintain a flexural strength of 66.95 ± 4.24 MPa with a flexural modulus of 60.42 ± 7.25 GPa. But the fracture mode gradually evolved to brittleness.     

Joining of SiC ceramics via a novel liquid preceramic polymer (V-PMS)

A novel liquid preceramic polymer (V-PMS) was synthsized by modifying polymethylsilane (PMS) with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane ([CH₃(CH₂CH)SiO]₄, D4Vi), for joining SiC ceramics under ambient pressure. The obtained V-PMS with a viscosity of 125 Pas at room temperature exhibits excellent thermal properties and bonding strength. The ceramic yield of V-PMS treated at 1200 °C under Ar atmosphere is 84.5%, which is 38.3% higher than the original PMS. The shear strengths of the SiC joints joined by V-PMS at 800 °C, 1000 °C and 1200 °C under N₂ atmosphere are 11.9 MPa, 34.5 MPa and 29.9 MPa, respectively. The excellent performances make the obtained V-PMS promising candidates for joining SiC ceramics in high-temperature applications.     

Multiple high-temperature resistant phases modified phosphate-based adhesive for engineering ceramic connection in extreme environment

The lower-strength defect of inorganic phosphate adhesive had been definitely improved by self-generating multiple high-temperature resistant phases. Compared to our previous product, the best bonding performance of this novel adhesive for mullite was increased by 270%, which was close to some popular preceramic polymer-based adhesives. The apparent shear strength at room temperature was up to 33.1?MPa after calcination at 900?°C, while the high-temperature strength researched 23.3?MPa at 900?°C and maintained above 17?MPa from 700° to 1200?°C. The reinforced effect of adhesive owed to the introduction of various Cu-based intermetallics, the premature generation of Al₄B₂O₁₈ at 900?°C, and the structure optimizing through the oxidization of Si and B₄C. Besides, the novel adhesive displayed good resistance to thermal-shock, especially for air-cooling test. After 15 thermal cycles in air, the residual strength of 1300?°C-calcined joints was still above 13?MPa (~40%).     

Reactive brazing Cf/SiC to itself and to Mo using the NiPdPtAu-Cr filler alloy

The NiPdPtAu-Cr filler alloy was proposed for joining C_f/SiC composites. The wettability on C_f/SiC composite was studied by the sessile drop method at 1200 °C for 30 min. Under the brazing condition of 1200 °C for 10 min, the C_f/SiC-C_f/SiC joint strength was only 51.7 MPa at room temperature. However, when used a Mo layer, the C_f/SiC-Mo-C_f/SiC joint strength was remarkably increased to 133.2 MPa at room temperature and 149.5 MPa at 900 °C, respectively. At the interface between C_f/SiC and Mo, Mo participated in interfacial reactions, with the formation of Cr₃C₂/Mo₂C reaction layers at the C_f/SiC surface. The improvement in the joint strength should be mainly attributed to the formation of MoNiSi. The C_f/SiC-Mo joint strength was 86.9 MPa at room temperature and 73.7 MPa at 900 °C, respectively. After 10 cycles of thermal shock test at 900 °C the C_f/SiC-Mo joint strength of 71.6 MPa was still maintained.     

A novel process with the characteristics of low-temperature bonding and high-temperature resisting for joining Cf/SiC composite to GH3044 alloy

Taking advantages of reaction composite brazing, transient liquid phase bonding (TLP) and partial transient liquid phase bonding (PTLP), a novel process with the characteristics of low-temperature bonding and high-temperature resisting was developed for joining C_f/SiC composite to GH3044 alloy by using (Cu-Ti) + C + Ni mixed powder filler. Under the bonding temperature (980 °C), the reaction between the liquid Cu-Ti alloy and C particles (reaction composite mechanism), composition homogenizations between the joining layer and Ni particles (PTLP mechanism) as well as Ni-based substrate (TLP mechanism) occurred to complete the transformation (Cu,Ti)_l + C_s + Ni_s → TiC_s + (Cu,Ni)_s. Thereby, a joint with high-temperature resistance and excellent mechanical properties was obtained in relatively short holding time. The melting-point of the joint (1050 °C) was obviously higher than that of Cu-Ti alloy (898 °C) in the filler. The bonded joints exhibited shear strengths of 229, 225 and 104 MPa at room temperature, 600 °C and 1000 °C, respectively.     

Preparation and performance of a heat-resistant organic adhesive obtained via a liquid SiC precursor

A heat-resistant organic adhesive rich in active SiH bonds and CHCH₂ bonds has been synthesized by modifying polymethylsilane with D4Vi. The structure and properties of the adhesive have been investigated by FTIR, GPC, TGA, XRD, bonding strength tests, and SEM. The results show that the obtained adhesive exhibits outstanding thermal stability and bonding properties. The ceramic yields of the adhesive treated in Ar or in air at up to 1200 °C were measured as 81% and 90.6%, respectively. The adhesive can maintain an amorphous state even when heat-treated at 1200 °C for 2 h in air. The room temperature shear strength of the adhesive was measured as 14.9 MPa, and this increased to a maximum value of 31.7 MPa after heat-treatment at 1000 °C for 2 h.     

Interfacial reaction behavior and bonding mechanism between liquid Sn and ZrO2 ceramic exposed in ultrasonic waves

Ultrasound-assisted dipping of ZrO₂ ceramics into molten Sn solder was performed to realize the low-temperature joining of ZrO₂ ceramics in this study. Scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction and X-ray photoelectron spectroscopy were employed to study the effects of ultrasonic vibration on the microstructure of Sn/ZrO₂ interface, and to elucidate the joining mechanism between Sn coating layer and ZrO₂ ceramic. Results showed that, after ultrasonically dipping in molten Sn for 1200 s, a pure Sn solder layer with a thickness of approximately 8–9 µm was coated on the ZrO₂ surface. The Sn coating layer exhibited excellent metallurgic bonding with ZrO₂ ceramic. A nano-sized ZrSnO₄ ternary phase, which was beneficial to the smooth transition of the lattice from Sn solder to ZrO₂ ceramic, was formed at the Sn/ZrO₂ interface. The formation of ZrSnO₄ interlayer was ascribed to the acoustic cavitation induced high-temperature reaction of Sn, O and ZrO₂ at the molten Sn/ZrO₂ ceramic interface. The tested average shear strength of ZrO₂/Sn/ZrO₂ joints was approximately 32 MPa, and the shearing failure mainly took place within the Sn solder layer.