Presentation on:- Diffusion Bonded Welding (DBW)

Table Of Content

INTRODUCTION CHARACTERSTICS WORKING PRINCIPAL WORKING PROCESS EXPERIMENTAL PROCEDURE FACTORS INFLUENCING DIFFUSION WELDING FILLER MATERIAL MATERIALS IN DIFFUSION WELD ADVANTAGES LIMITATIONS APPLICATIONS REFERENCES

Diffusion WELDING:-

• Diffusion welding (DFW) is a solid state welding process by which two metals (which may be dissimilar) can be bonded together.

• Diffusion involves the migration of atoms across the joint, due to concentration gradients. The two materials are pressed together at an elevated temperature usually between 50 and 70% of the melting point.

• The pressure is used to relieve the void that may occur due to the different surface topographies.

• The pressure used is in the range of 35 to 70 MPA.

CHARACTERISTICS

• It operates on the materials science principle of solid-

state diffusion, wherein the atoms of two solid, metallic surfaces intermingle over time under elevated temperature. Diffusion bonding is typically implemented by applying both high pressure and high temperature to the materials to be welded.

• Diffusion welding use for metal to metal and metal to non- metals.

• The characteristic features of this process are that it does not introduce macroscopic deformations or relative motion in either of the welded parts and that it does not melt base metals.

• Diffusion bonding is mostly oused for jobs either difficult or impossible to weld by other source. Exp: zirconium and beryllium; materials with very high melting points ..

CHARACTERISTICS

• Diffusion bonding is mostly used for jobs either difficult or impossible to weld by other source. Exp: zirconium and beryllium; titanium and copper, materials with very high melting points ..

• Diffusion bonding involves no liquid fusion or filler metal.

• The join tends to exhibit both the strength and temperature resistance of the base metal.

Diffusion Welding Working Principles

• Diffusion Welding Working Principles 1st stage deformation forming interfacial boundary.

2nd stage Grain boundary migration and pore elimination.

3rd stage Volume diffusion and pore elimination.

PRINCIPAL

Process

• At the microscopic level, diffusion bonding occurs in three simplified stages:-

• Before the surfaces completely contact, asperities (very small surface defects) on the two surfaces contact at the microscopic level and plastically deform. As these asperities deform, they interlink forming interfaces between the two surfaces.

• Elevated temperature and pressure causes accelerated creep in the materials; grain boundaries and raw material migrate and gaps between the two surfaces are reduced to isolated pores.

• Material begins to diffuse across the boundary of the abutting surfaces, confusing this boundary and creating a bond.

Process

Working Process

• Diffusion bonding is performed by clamping the two pieces to be welded with their surfaces each other. Prior to welding, these surfaces must be machined to as smooth a finish as economically viable, and kept as free from chemical contaminants or other detritus as possible.

• Any intervening material between the two metallic surfaces may prevent adequate diffusion of material. Once clamped, pressure and heat are applied to the components

EXPERMENTAL PROCEDURE

• For this purpose, titanium and copper materials joined through diffusion welding method.

• The specimens for the diffusion welding (Ti and Cu) were prepared in the sizes of 10 mm in diameter and 10 mm in length.

• The prepared specimens were ground with SiC abrasive papers of

various grit sizes (240, 400, 800 and 1200) and polished to mirror surface finish using a 1 μm diamond paste.

• Finally, all the specimens were cleaned by degreasing in acetone.

EXPERMENTAL PROCEDURE

• Diffusion welding was made in an argon atmosphere in the bonding chamber equipment.

• In order to eliminate the oxidation problem, Ar gas was introduced into the test chamber 5 min before the welding and kept (continued) during welding.

• 3 MPa pressure was applied during the diffusion bonding.

• Important diffusion bonding process parameters (bonding temperature and holding time) were identified in Table by carrying out preliminary tests.

• Heating and cooling rates of 20 °C/min were employed during the heating and cooling cycles.

Diffusion welding equipment (a) photo and (b) schematic.

EXPERMENTAL PROCEDURE

• When the bonding process was completed, the specimens were cooled to room temperature in the furnace.

Factors Influencing Diffusion Welding• (Relation between Temperature and Diffusion Coefficient)

• Temperature• D = D0 e -Q/KT

– D = Diffusion coefficient– D0 = Diffusion constant– Q = Activation energy– T = Absolute temperature– K = Boltzman’s constant

4.• X = C (Dt)1/2 = Diffusion Length

– X = Diffusion length – C = A constant– D = Diffusion coefficient (see previous slide)

t =Time

Factors Influencing Diffusion Welding

• The diffusion can be achieved when one keeps two pieces in intimate contact under pressure.

• By using heat, the bonding time can be further reduced as the diffusion process gets accelerated through heat.

• The heat applied is much lower than the melting points of metals.

• The pressure needs to be kept optimum such that there is no plastic deformation.

Filler Material

• A filler material can be used and is kept between the two metals to be joined.(silver layer,nikel layer)

• The filler material if used its thickness is in the range of 5 to 25 microns only.

• In such a case it is expected that the temperature required for bonding is reduced by the formation of a eutectic alloy.

• Thus, the filler metal diffuses into the two metal plates and forms a eutectic joint.

• Although filler metal is in principle not required for Diffusion welding, it has been found that a foil of suitable materials placed at the interface can sometimes facilitate the process.

Materials In Diffusion Weld

• It Can be Diffusion welded Titanium alloys, nickel alloys, aluminum alloys, as well as different combinations of materials not easily joined by traditional means.

• Steels are preferably welded by alternative more economic methods.

• But large, flat surfaces of low carbon steel have been

• Diffusion welded without filler metal under the proper conditions

Advantages • This solid state process avoids pitfalls of fusion welding .

• Dissimilar materials welds are possible.

• Properties and microstructures remain similar to those of base metals.

• Multiple welds can be made in one setup at the same time.

• Produces a product finished to size and causes minimal deformation.

• Presents less shrinkage and stresses compared to other welding process.

• Highly automated process does not need skillful workforce.

Limitations

• Costly equipment especially for large weldments.

• Costly preparation with smooth surface finish and exceptional cleanliness.

• Protective atmosphere or vacuum required.

• Long time to completion.

• Not suited to high production rates.

• Difference in thermal expansion of members may need special attention.

• Limited nondestructive inspection methods available

APPLICATION

• Application in titanium welding for aero-space vehicles.

• Diffusion welding of nickel alloys include Inconel 600, wrought Udimet 700, and Rene 41.

• Dissimilar metal diffusion welding applications include Cu to Ti, Cu to Al, and Cu to Cb-1%Zr. Brittle intermetallic compound formation must be controlled in these applications.

BIBILOGRAPHY

http://www.sciencedirect.com/science/article/pii/S0261306912000350

(Kemal Aydın , Yakup Kaya , , Nizamettin Kahraman)

http://www.sciencedirect.com/science/article/pii/S0261306904001967

Wikipedia

Google

THANK YOU