Diffusion welding (Bonding) Process

Diffusion welding 

Preface

The recent development of solid-state welding technology has further enabled the production of welds in various metals. Diffusion welding is also a type of solid state welding.

Definition of diffusion welding

Diffusion welding / bonding is a solid-state welding process, in which welding is performed with applications of pressure and elevated temperature for coalescence of faying surfaces. This is done to cleaned carefully and mated metal surfaces so that they actually grow together by atomic diffusion.

.Theory of Diffusion welding

The diffusion welding process develops in two stages.

First stage

The first step is to  bring the intimate metal into contact with the metal. This is done by the application of pressure which distorts the roughness of the substrate and disrupts and expands the above mentioned surface layers and contaminants.

Second stage

The second stage consists of diffusion and grain growth to complete the weld and finally to eliminate the interface formed in the previous phase. The second phase induces complete metal bonding in the area of ​​contact.

Method of diffusion welding (bonding)

Diffusion welding includes the following types of methods.

• Gas-pressure bonding

The joining parts are held together in intimate contact and then heated to around 815 degrees centigrade. During heating, an inert gas pressure is created on all surfaces of the parts to be welded. Non-ferrous metals are joined with the help of the gas pressure bonding method.

• Vacuum fusion bonding

The parts joining it are pressed together mechanically or hydraulically. A welding press which is used for diffusion welding, is employed in forging and is equipped to make pressures from three directions.

The heating is done in the same way as in gas pressure bonding. These processes are performed in a vacuum chamber. Nevertheless, more pressure than can be applied to gas pressure bonding can be applied in this process, steel and for that vacuum fusion bonding is used. 

The temperature and pressure required for the propagation relationship of steel is about 1150 degrees centigrade and 700 kg / Cm²  

• Eutectic fusion bonding

It is a low temperature diffusion welding process in which a thin plate of some other material, such as nickel, is added. As the pieces are heated to an elevated temperature, the filler material expands and forms an Eutectic compound with the base metals.

Parameters of Diffusion Welding

The parameters of diffusion welding are as follows:

1. Pressure 
2. Temperature 
3. Time Surface

Uniform pressure assures stability of bond formation and The elevated temperature performs the important function of increasing the surface energy (mobility of the atom).Time is a dependent process parameter such as an increase in temperature, reducing the time required to complete the confounding process.

Other parameters

1. Metallurgical Factors 
2. Surface Preparation.

Advantages of Diffusion welding

1. The main advantage of diffusion welding is that the weld metal having essentially the same properties as the base metal.
2. Dissimilar metal can be welded by this process also.

Application of Diffusion welding

This process is mostly applied in the nuclear power industries to fabricate components, manufacture composites materials, and use in the aerospace missile and rocket industries

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