Pressure-less joining of SiCf/SiC composites by Y2O3–Al2O3–SiO2 glass: Microstructure and properties

In this study, Y₂O₃–Al₂O₃–SiO₂ (YAS) glass was prepared from Y₂O₃, Al₂O₃, and SiO₂ micron powders. Thermal expansion coefficient of as-obtained YAS glass was about 3.9 × 10⁻⁶, matching-well with that of SiC_f/SiC composites. SiC_f/SiC composites were then brazed under pressure-less state by YAS glass and effects of brazing temperature on microstructures and properties of resulting joints were investigated. The results showed that glass powder in brazed seam sintered and precipitated yttrium disilicate, cristobalite, and mullite crystals after heat treatment. With the increase in temperature, joint layer gradually densified and got tightly bonded to SiC_f/SiC composite. The optimal brazing parameter was recorded as 1400 °C/30 min and shear strength of the joint was 51.7 MPa. Formation mechanism of glass-ceramic joints was proposed based on combined analysis of microstructure and fracture morphology of joints brazed at different temperatures. Thermal shock resistance testing of joints was also carried out, which depicted decline in shear strength with the increase of thermal shock times. The strength of the joint after three successive thermal shock cycles at 1200 °C was 35.6 MPa, equivalent to 69% of that without thermal shock.     

Vacuum brazing Mo using Ti-Ni-Nb braze alloys

A novel approach of brazing Mo using three clad Ti-Ni-Nb foils, 40Ti-35Ni-25Nb, 50Ti-35Ni-15Nb and 60Ti-15Ni-25Nb in wt.%, has been performed in the experiment. Similar microstructural evolution of the joint is observed for three foils. The joint using 60Ti-25Ni-15Nb foil brazed at 1250 °C for 600 s demonstrates the highest bending strength of 526 MPa. The clad Ti-Ni-Nb foils show potential in brazing Mo for industrial application.     

A correlation study of mechanical strength of resistance spot welding of AA5754 aluminium alloy

AA5754 aluminium alloy was resistance spot welded (RSW) to produce 27 different joint stack-ups with differing process parameters and corresponding weld quality. Quasi-static joint strength was evaluated for three test geometries; lap-shear, coach-peel and cross-tension. The results derived from over 1000 samples demonstrate various fundamental relationships. For lap-shear strength, a strong relationship with weld nugget diameter was observed; whilst discrete strength levels were found for coach-peel test geometry, depending on the governing metal thickness of the parent sheet for the various stack-ups. For cross-tension strength; there is a relationship with nugget diameter; but data are sensitive to nugget periphery defects. These fundamental relationships provide a set of generalised design guidelines for RSW of aluminium that will have significant relevance to manufacturing communities.     

The analysis of lock forming mechanism in the clinching joint

In this study, the effect of the process parameters of the clinching process on the joinability of advanced high-strength steel was investigated using finite element analysis (FEA). The effect of die geometrical parameters on the achieved joint lock size and maximum forming force has been determined. It has been determined that the die groove width is the most important parameter affecting the material flow effect and energy consumption of the joining process. From the result, the die radius, die depth, and die groove shape were mainly affected by the joinability of advanced high-strength steel H320LA.     

Brazing of Al2O3 to Ti-6Al-4V alloy with in situ synthesized TiB-whisker-reinforced active brazing alloy

65.9Cu-24.4Ti-9.7TiB₂ (wt.%) composite filler was used to join Al₂O₃ and Ti-6Al-4V alloy. 30 vol.% TiB whiskers were in situ synthesized as reinforcements in joints. Brazing temperature was 890 °C, 910 °C, 930 °C, 950 °C and 970 °C, and the holding time was 0, 5, 10, 20, and 30 min. The microstructure and mechanical properties of brazed joints were analyzed by scanning electron microscope equipped with energy dispersive spectrometer, shear test and nano-indentation test. Results show that reaction layer Ti₄(Cu,Al)₂O forms at Al₂O₃/brazing alloy interface. The reaction between TiB₂ powders and Ti atoms in brazing alloy brings on in situ synthesizing TiB whiskers in (Ti,Al)₂Cu and AlCu₂Ti intermetallics. Formation of TiB whiskers minimizes the mismatch of thermal expansion coefficient between Al₂O₃ and brazing alloy, and makes the ductile-rigid-ductile multiple layer present in joints, which reduces residual stress of joints. The maximum shear strength of joints can reach 143.3 MPa when the brazing temperature is 930 °C, and holding time is 10 min.     

陶瓷材料的微波焊接研究

陶瓷材料微波焊接是一门具有实用价值和应用前景的新颖的焊接技术。它与常规的陶瓷焊接比较具有:(1)能耗低;(2)升温快;(3)接头质量高等优点。本文对微波焊接的特点、机理、设备、式艺及发展和展望进行了较全面分析和讨论。     

Design and manufacture of an impact–electric current discharge joining machine

An impact–electric current discharge joining machine, which can simultaneously apply impact load and electric current, has been designed and manufactured to produce a high-strength joint between materials with little change in their appearance. The objective functions of the designed and manufactured impact–electric discharge machine are almost satisfied. Partial joining is achieved between FCD450/FCD450 samples and between FCD450/Al samples and the joints exhibit low fracture stress. Process parameters can be controlled to improve joint strength, by adjusting the setting values of the functions provided in the machine.     

Effect of Applied Pressure on the Joining of Combustion Synthesized Ni3Al Intermetallics with Al Alloy

We focused on the surface reinforcement of ligth weight casting alloys with Ni-AI intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components.In our previous works,green compact of elemental Ni and Al powders were reacted to form Ni-3Al intermetallic compound by SHS （Self-propagating high temperature synthesis） reaction with the heat of molten Al alloy and simultaneously bonded with Al casting alloy.But some defects such as tiny cracks and porosities were remained in the reacted compact.So we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting process.The compressed Al alloy bonded with the Ni-3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy （SEM）.The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy （EDS） and electron probe micro analysis （EPMA）. Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al alloy.The porosities observed in the reacted Ni-3Al compact were filled up with the liquid AI alloy.The Si particles from the molten Al alloy were detected in the pores of reacted Ni-3Al intermetallic compact.The Al casting alloy and Ni-3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.     

Joining of titanium diboride-based ultra high-temperature ceramics to refractory metal tantalum using diffusion bonding technology

The use of ultra-high temperature ceramics (UHTCs) requires effective methods to overcome the problems associated with manufacturing parts with complex shapes. In this study, a titanium diboride (TiB₂)-based ultra-high-temperature ceramic, TiB₂-20 vol.%TiC-20 vol.%SiC (TTS), was joined to refractory metal tantalum (Ta) using titanium (Ti) interlayer. The interface microstructure and mechanical properties of joints obtained at different bonding temperatures were investigated. The bonding mechanism of the joint was discussed based on TEM analysis and theoretical calculation. The results revealed that a (Ti, Ta)B + TiC + Ti₅Si₃ reaction layer formed adjacent to the TTS ceramic substrate while a β-(Ta, Ti)+β-(Ti, Ta)+α-Ti layer formed adjacent to the Ta substrate. The α-Ti was gradually replaced by β-(Ta, Ti) and β-(Ti, Ta), and the reaction layer of the ceramic side became thicker as the bonding temperature increased. The maximum joint shear strength of room temperature was 176 MPa when the joint was bonded at 1200 °C for 60 min under 20 MPa, and cracks propagated in the ceramic. The shear strength of the joint tested at 800 °C was 86 MPa, and fracture occurred at the β-(Ti, Ta).     

Microstructure,mechanical and optical properties of MgAl2O4/MgAl2O4 joints bonded using CaO-Al2O3-SiO2 glass filler

Transparent MgAl₂O₄ ceramics were bonded by using CaO-Al₂O₃-SiO₂ (CAS) glass filler. The CAS glass filler exhibited the same thermal expansion behavior as MgAl₂O₄ ceramic and excellent wetting ability on the surface of MgAl₂O₄ ceramic. When the cooling rate of 15 °C/min was used, no interfacial reaction was observed and the amorphous brazing seam could be obtained. However, low joining temperature (1250 °C) led to the formation of pores and high joining temperature (1400 °C) resulted in the formation of cracks. Furthermore, the slow cooling rate of 5–10 °C/min induced the crystallization of CaAl₂Si₂O₈ and Mg₂Al₄Si₅O₁₈ due to the dissolution of MgAl₂O₄ substrate. The optimal flexural strength of 181–189 MPa was obtained when the joining temperature and cooling rate were 1300–1350 °C and 15 °C/min respectively. Moreover, the in-line transmittance of the joint at 1000 nm was 82.1%, which was slightly lower than that of MgAl₂O₄ ceramic (85.6%).