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The secret communication between metals: How does diffusion welding allow different metals to be perfectly combined?
Diffusion welding is a robust welding technique that has a wide range of applications in metal processing, enabling the perfect joining of similar and dissimilar metals. Its operating principle is solid-state diffusion, which allows the atoms on the surfaces of two solid metals to penetrate each other over time. This process is generally carried out in an environment above room temperature, and the temperature range is about 50% to 75% of the absolute melting point of the material. In addition, although some degree of weak welding can be achieved at room temperature, in practice diffusion welding is often performed at high pressure and temperature, and this method is particularly common in the aerospace and nuclear energy industries.
Diffusion welding does not involve liquid melting and typically does not require additional filler metal.
Looking back at the history of diffusion welding, this technology can be traced back centuries. For example, in jewelry making, craftsmen will use a technique called "gold filling" to combine gold with copper. These craftsmen first pressed solid gold into thin sheets, which they then placed on a copper substrate and applied weight. Next, the combination is heated in a high-temperature oven until the gold flakes are fully bonded to the copper substrate. The modernization process of this phenomenon was elaborated in 1953 by the Soviet scientist N.F. Kazakov.
Characteristics of diffusion welding
The characteristic of diffusion welding is that in addition to not requiring liquid melting, it can also maintain the strength and temperature resistance of the base material. During this process, the material undergoes very little plastic deformation, the residual stress is relatively low, and no pollution is produced. Theoretically, diffusion welding can be performed on joint surfaces of any size without increasing the processing time; however, in practice, the size of the joint surface will be affected by the required pressure and physical limitations.
Diffusion welding is suitable for joining similar and dissimilar metals, and can be used for reactive and refractory metals, or metal sheets of varying thicknesses. Due to its relatively high cost, diffusion welding is often used for workpieces that are difficult or impossible to weld otherwise, such as clay-metal alternatives with thin cross-sections, or materials with extremely high melting points, such as tungsten. Diffusion welding is therefore particularly suitable for applications where strength and high-temperature stability are particularly important.
Temperature dependence
Steady-state diffusion depends primarily on the diffusion flux through the cross-section of the joint surface. Fick's first law of diffusion provides the mathematical formula for diffusion flux, which will not be listed in detail here. Simply put, by calculating the diffusion of masses or atoms, one can understand the relationship between time requirements and diffusion coefficients. During the entire welding process, the only parameter that can be controlled is temperature.
Welding process
When two materials have similar crystal structures, the process of diffusion welding begins by bringing the surfaces of two pieces of metal together. Before welding, these surfaces need to be polished to an economically viable smoothness and kept as free of chemical contamination as possible. Then, pressure and heat are applied to keep the parts in contact with each other for an extended period of time. Surface treatment during welding, such as polishing, etching and cleaning, are important factors affecting the diffusion welding process.
The three simplified processes of diffusion welding include micro deformation, diffusion controlled mass transfer and interface diffusion.
Advantages of diffusion welding
Diffusion welding can produce high-quality joints without obvious faults or pores, and the surface has the same physical and mechanical properties as the base material. Once welding is complete, the reliability and durability of the joint can be tested through methods such as tensile testing. In addition, diffusion welding can realize the production of high-precision components with complex shapes and is widely used in fields such as electronics, aerospace, nuclear energy and microfluidic technology.
Applicability and development prospects
Currently, diffusion welding is widely used in the aerospace industry to achieve the manufacturing of complex parts and effectively reduce manufacturing costs and material waste. In military aircraft, the use of diffusion welding to protect expensive strategic materials has shown remarkable results. It not only improves production efficiency, but also enhances the diversity and breadth of material use.
With the continuous development of technology, diffusion welding is expected to achieve breakthroughs in more application fields, and to achieve higher benefits when combined with other process technologies. How will future metal joining technology change our product design and manufacturing processes?
