金属冷压焊结合机理的试验研究

针对金属冷压焊的结合机理,采用中子活化、电镜扫描、光谱分析等测试手段对金属冷压焊接头界面原子扩散行为进行了综合试验测定,发现在所测试的冷压焊接头中不存在异种金属间的相互扩散行为。进一步对冷压焊接头界面区的透射电镜观察分析表明：接头界面区是由挤压碎化的细晶构成,碎化的细晶在界面处相互咬合增加了相焊金属间物理接触面积,形成碎化细晶之间的晶间结合,无需金属原子间的扩散就能实现结合。根据上述分析结果,实现了非共格金属间及液相、固相不相溶金属间的对接冷压焊。并进一步说明了各种不同组配异种金属间的冷压焊接性     

Joining of SiC ceramics by combining NITE-SiC interlayer and its thickness control

Combined with the thickness control of interlayers (∼10 µm and ∼60 µm), SiC nano-powders with Al₂O₃-Y₂O₃-MgO-CaO additive (NITE-SiC) were used as the joining materials to achieve the low-temperature joining of SiC ceramics. Some residual pores were observed in the interlayer with a thickness of ∼60 µm after joining at 1650 ℃, and the shear strength of SiC joints measured was 39.3 ± 5.5 MPa. Observations showed the fracture of joints occurred at the interlayer. When the thickness of the interlayer decreased to ∼10 µm, no cracks or porosity were observed at the interface region after joining at 1650 ℃. The shear strength of SiC joints increased to 69.5 ± 8.9 MPa, and the fracture originated from the matrix. The results demonstrated using NITE-SiC with Al₂O₃-Y₂O₃-MgO-CaO additive as the joining layer and reducing the thickness of the interlayer could lower the joining temperature and significantly improve the mechanical strength of joints.     

Fast joining of α/β-SiAlON ceramic with WC-8Co cemented carbide using Ti-Cu foils by spark plasma sintering

The α/β-SiAlON ceramic was joined to WC-8Co cemented carbide with Ti-Cu by spark plasma sintering. Interfacial microstructure and phases of the joints were studied. The effects of joining temperature, holding time, and pressure on the shear strength of the α/β-SiAlON/WC-8Co joints were investigated. The typical interfacial microstructure of α/β-SiAlON/Ti-Cu/WC-8Co joint was α/β-SiAlON/TiN + Ti₅Si₃ + TiCu + TiCu₂ + Cu + Cu-Co solid solution/WC-8Co. In comparison with pressure, temperature and holding time had greater impacts on the degree of interfacial reaction during the joining process. When the joining temperature, holding time, and pressure were 900 °C, 5 min and 40 MPa, the highest shear strength (246.3 MPa) of α/β-SiAlON/WC-8Co joint was achieved, which is qualified for the high-speed machining of superalloy.     

Diffusion bonding of transparent ceramics by spark plasma sintering (SPS) complemented by hot isostatic pressing (HIP)

Diffusion bonding is a viable technique for fabricating larger parts or composite transparent ceramics. Spark plasma sintering (SPS) and hot isostatic pressing (HIP) allow for simultaneous application of high temperature and pressure, making them suitable for bonding various materials, including transparent ceramics. In this study, we demonstrated the combined use of SPS followed by HIP for successful diffusion bonding of transparent MgAl₂O₄ (spinel) and Y₃Al₅O₁₂ (YAG) ceramics. The YAG samples had superior surface quality and were adequately bonded using SPS alone, while rougher spinel samples showed inadequate bonding initially due to insufficient surface contact. However, subsequent HIP treatment effectively closed the voids at the interface and promoted grain growth across the joint, resulting in a strong seamless bond. The combination of SPS and HIP, as a two-step process, holds promise for diffusion bonding of ceramics and offers a potential solution for compensating surface quality issues in the bonded parts.     

Crystallization behavior of BaO–CaO–SiO2–B2O3 glass sealant and adjusting its thermal properties for oxygen transport membrane joining application

In this work, the thermal stability of a BaO–CaO–SiO₂–B₂O₃ glass sealant, named “H”, was investigated by differential scanning calorimetry (DSC). The crystallization behavior of glass H as the sealant matrix was investigated by a combination of experimental X-ray diffraction (XRD) analysis and thermodynamic simulation with the FactSage package. A good agreement was found between the Rietveld refinement of XRD experiments and the FactSage simulation. Particular attention was also given to the influence of the Sr₂SiO₄ filler added to the glass matrix “H” on the thermal expansion and microstructures of glass-Sr₂SiO₄ composites by means of dilatometry and scanning electron microscopy (SEM). The reinforced 20 wt% Sr₂SiO₄ composite (HS2S20) showed excellent properties and, thus, its joining performance was investigated using SrTi_0.75Fe_0.25O_3-δ (STF25) and Aluchrom as promising oxygen transport membrane (OTM) and counterpart, respectively. The joining behaviors were investigated by comparing different joining temperatures. 920 °C is the best joining temperature for HS2S20 sealant.