[재료공학]Diffusion bonding

소개글

Diffusion bonding 에 대한 소개와 각상에 따른 재료에 따른 방법.

목차

Introduction
Process mechanism
Solid phase diffusion bonding
Liquid phase diffusion bonding/diffusion brazing
Superplastic forming/diffusion bonding
Diffusion bonding - Ceramics and ceramic/metal joints
Summary

본문내용

Introduction
Diffusion bonding is a solid-state joining process capable of joining a wide range of metal and ceramic combinations to produce both small and large components. The process is dependent on a number of parameters, in particular, time, applied pressure, bonding temperature and method of heat application. Other examples of solid-state joining include cold pressure welding, friction welding, magnetically impelled arc butt (MIAB) welding and explosive welding.
Diffusion bonding itself can be categorised into a number of variants, dependent on the form of pressurisation, the use of interlayers and the formation of a transient liquid phase. Each finds specific application for the range of materials and geometries that need to be joined.

Process mechanism
In its simplest form, diffusion bonding involves holding pre-machined components under load at an elevated temperature usually in a protective atmosphere or vacuum. The loads used are usually below those which would cause macrodeformation of the parent material(s) and temperatures of 0.5-0.8Tm (where Tm = melting point in K) are employed. Times at temperature can range from 1 to 60+ minutes, but this depends upon the materials being bonded, the joint properties required and the remaining bonding parameters. Although the majority of bonding operations are performed in vacuum or an inert gas atmosphere, certain bonds can be produced in air.
An examination of the sequence of bonding (Fig.1) emphasises the importance of the original surface finish. To form a bond, it is necessary for two, clean and flat surfaces to come into atomic contact, with microasperities and surface layer contaminants being removed from the bonding faces during bonding. Various models have been developed to provide an understanding of the mechanisms involved in forming a bond. First they consider that the applied load causes plastic deformation of surface asperities reducing interfacial voids. Bond development then continues by diffusion controlled mechanisms including grain boundary diffusion and power law creep.

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