File:Chapter 10 Diffusion bonding of metal alloys in aerospace and other applications.jpg

English: 10 Diffusion bonding of metal alloys in aerospace and other applications

Ho-Sung Lee Korea Aerospace Research Institute, Daejeon, Republic of Korea

10.1 Introduction The diffusion-bonding process is one of the solid-state bonding processes. During a hot bonding process, two components are typically joined under pressure, with close contact between the surfaces and at a temperature below the melting point of the parent metal. In the case of diffusion bonding, it is important that the fusion temperature is not reached, and filler material is not needed. Diffusion bonding occurs as a result of diffusion of the interface atoms of the bonded materials. Diffusion bonding is an attractive manufacturing method for aerospace applications, where mechanical properties in the bond area and a sound metallurgical bond are important. It is a different process to brazing or the TLP (Transient Liquid Phase) bonding process, in which a foreign metal with a lower melting point is used to weld similar or dissimilar metals together. As a diffusion bond is formed by atomic migration across an interface in a solid state, there is no metallurgical discontinuity at the interface, and the mechanical properties and microstructure at the bonded region are similar to those of the base metal. For example, titanium alloys can easily be joined by diffusion bonding owing to the ability of titanium to dissolve its own oxide in a vacuum. In combination with superplastic forming (SPF), diffusion bonding is a solid-state process that is defined as one in which the components being joined undergo macroscopic deformation by no more than a few per cent, without a liquid phase. The process is dependent on various parameters, in particular time, applied pressure and bonding temperature, to promote

microscopic atomic movement and ensure a complete metallurgical bond.