CONTENTS: 1. Introduction ------------------------------------------------------- Page (1-2) 2. Theory ------------------------------------------------------- Page (3) 3. Process – Diffusion Bonding -------------------------------------------------- Page (3-4) 4. Diffusion Bonding Set-up /Equipment -----------------------------------------Page (4-5) 5. Factors affecting the process -------------------------------------------------- Page (5-6) 6. Metallurgical Factors ----------------------------------------------------Page (6) 7. Material Combinations used in the process -----------------------------------Page (6) 8. Types of Diffusion Bonding ----------------------------------------------------Page (6-7) 9. Diffusion Bonding & Magnetic Materials -------------------------------------Page (7-8) 10. Applications --------------------------------------------- Page (8-9) 11. Advantages -------------------------------------------------------Page (9) 12. Disadvantages -------------------------------------------------------Page (9) 13. References -------------------------------------------------------Page (10) . On the other hand. which is equal to the base metals. Diffusion bonding offers many advantages.INTRODUCTION: Diffusion bonding or diffusion welding is a solid-state welding technique used in metalworking. this advantage joining process requires several strictly controlled condition: clean and smooth contacting surfaces which are free from oxides.. etc. approximately 50-70% of the absolute melting temperature of the materials. wherein the atoms of two solid. high temperature condition to promote diffusion process.The solid phase diffusion bonding of the product is used in various industrial fields to make making to high performance and making to a high function near-net shape in addition. The microstructure at the bonded region is exactly the same as the parent metals. It operates on the principle of solid-state diffusion. capable of joining similar and dissimilar metals. metallic surfaces intersperse themselves over time. mainly the strength of the bonding line. This is typically accomplished at an elevated temperature. or pieces of varying thicknesses. reactive and refractory metals. . and the join tends to exhibit both the strength and temperature resistance of the base metal(s). It may be performed on a join surface of theoretically any size with no increase in processing time. or very little. Figure 1: Microstructure of Diffusion Bonding Diffusion bonding involves no liquid fusion. and often no filler metal. plastic deformation. No weight is added to the total. Unlike other joining processes the diffusion bonding process preserves the base metal microstructure at the interface. and there is no contamination from the bonding process. The materials endure no. It may be performed with similar and dissimilar metals. Very little residual stress is introduced. practically speaking. the surface tends to be limited by the pressure required and physical limitations. More importantly no localized thermal gradient is present to induce distortion or to create residual stresses in the component. Diffusion bonding is an attractive manufacturing option for joining dissimilar metals and for making the component with critical property continuity requirements. and D0 is a temperature-independent preexponential factor that depends on the materials being joined. This is widely used to join refectory materials in aerospace and nuclear industries. Fick's first law of diffusion states: where J is the diffusion flux. which changes by only incremental amounts through the joint. Equating the two equations and rearranging. Another form of Fick's law states: where M is defined as either the mass or amount of atoms being diffused. and dC/dx is the concentration gradient through the materials in question. T is the thermodynamic temperature experienced during the process. and the diffusion coefficient. R is the universal gas constant. The negative sign is a product of the gradient. the only term in this equation within control is temperature. time required is largely dependent on the concentration gradient. A is the cross-sectional area. This bonding process conducted in vacuum or in inert environment to reduce oxidation. For a given joint. PROCESS: . The diffusion coefficient is determined by the equation: where Qd is the activation energy for diffusion. and t is the time required. THEORY: Steady state diffusion is determined by the amount of diffusion flux that passes through the cross- sectional area of the mating surfaces. D is a diffusion coefficient. we achieve the following result: As mass and area are constant for a given joint. local deformation at the interface surface due to creep and yield take place. both the plates properly diffused into one another which makes a strong joint. The temperature range is about 50-60% of melting temperature. At the starting stage of this process. The temperature applied by the furnace heating or electric resistance heating. The high pressure is applied by a hydraulic press. Now both the plates are clamped and placed one over another. This diffusion can be accelerated by the application of high temperature. First both the welding plate surfaces prepared for welding. Diffusion means movement of molecules or atoms from high concentration region to low concentration region. The interface surfaces should be machined. This assembly placed into a vacuum chamber or in a inert environment. This joint has same properties or strength as the base material. This conditions are maintained for a long duration of time for proper diffusion.This process works on basic principle of diffusion. both the interface surfaces made equally flat which is basic requirement of diffusion process. This temperature does not melt the welding plates. dead weight or by the differential gas pressure. Now the diffusion takes place which form a interface boundary. In this process. The working of diffusion bonding can be summarized as follow. This is fundamental principle of diffusion welding. . The interface boundary disappear which form a clean joint. This whole process takes place in vacuum or in inert environment which protects the welding plates form oxidation. After a long period of time. A high pressure and temperature applied on this assembly to start diffusion. This high pressure force starts diffusion between interface surfaces. cleaned and polished well which remove all chemical contaminants from the surface. In this welding process both the welding plates are placed one over other in high pressure and temperature for a long period of time. This protects the welding surface from oxidation. Any contaminant particle can be reduced diffusion between welding plates. . Fixed Rod 3. Bonding Dies 6. Loading Equipment( Hydraulic/Mechanical) 2. Movable Rod 4. Vaccum Facility 5. Stage to carry specimens .DIFFUSION BONDING SETUP – EQUIPMENT: 1. Rough initial surface finishes generally adversely affect welding by impeding the first stage and leaving large voids that must be eliminated during the later stages of welding 4. it is not an independent variable. Service environment METALLURGICAL FACTORS THAT INFLUENCE THE PROCESS: Two factors of particular importance with similar metal weld are allotropic transformation and micro structural factors that tend to modify diffusion rates. Pressure is necessary only during the first stage of welding to produce a large area of contact at the joining temperature. The time required to form a joint depends upon the temperature and pressure used. Allotropic transformation (phase transformation) occurs in some metals and alloys. Removal of pressure after this stage does not significantly affect joint formation. Temperature is the most influential variable since it determine the extent of contact area during stage one and the rate of diffusion which governs void elimination during the second and third stages of welding. 5. premature removal of pressure before completion of the first stage is detrimental to the process. 2. 3. Production tooling design 6. However. This tends . The important of the transformation is that the metal is very plastic during that time.PARAMETERS THAT AFFECT THE PROCESS: 1. When using a diffusion-activated system. This means of manufacture significantly reduce the parts count relative to fabricate structures. it is desirable to heat the assembly for some minimum time either during or after the welding process to disperse the high diffusivity element away from the interface. Another means of enhancing diffusion is alloying or more specially. to permit rapid interface deformation at lower pressures in much the same manner as does recrystallization. the high concentration of the element at the joint may produce metallurgically unstable structures. introducing elements with high diffusivity into the systems at the interface. If this is not done. Combining the two processes of SPF and diffusion bonding in particular as concurrent processes. Diffusion rates are generally higher in plastically deformed metals as they recrystalize. provides a potential for considerable cost and weight saving when compared with conventional fabricated structures which are typical of aerospace structures. Diffusion bonding is often combine with superplastic forming (SPF) for aerospace titanium structures. Alloying must be controlled to avoid melting at the joint interface. Cost saving accrue from the ability to form complex structure from simple starting blanks (in most cases flat blanks) and to form this into a complete structure in one operation. . The function of a high diffusivity element is to accelerate void elimination. In this case. Dissimilar metals may be joined with a third metal between the faying surfaces to enhance weld formation either by accelerating diffusion or permitting more complete initial contact in a manner similar to category (2) above. 2. In this situation-required pressures. Two dissimilar metals may be joined directly where diffusion-controlled phenomena occur to form a bond. the layer may promote more rapid diffusion or permit increased micro deformation at the joint to provide more complete contact between the surfaces. Similar metals can be joined with a thin layer of a different metal between them. Similar metals may be joined directly to form a solid-state weld. 4. This interface metal may be diffused into the base metal by suitable heat treatment until it no longer remains a separate layer.METAL COMBINATIONS USED: 1. temperatures. times are dependent onlyaccount the characteristics of the metals to bejoined and their surface preparation. 3. SOME METALS AND MATERIALS COMMONLY USED: Copper Titanium Molybdenum Alumninum Oxide Magnesium Silver Gold Aluminium Platinum Stainless Steel Other Special Alloys . Thin sheet diffusion bonding Massive diffusion bonding is a process used in the manufacture of heavy structure from plate elements. Massive diffusion bonding 2. The essential advantages of this manufacturing technique are its ability to produce heavy sections with a much-improved material utilization relative to conventional processes such as machining from solid. These are : 1. .TYPES OF DIFFUSION BONDING: Two types of diffusion bonding processing have been investigated in the development of low cost structure. This process ensures uniform pressure over the whole bond area and enables mismatch between the mating faces to be overcome by the SPF properties of the material. . bonding is affected by means of inert gas pressure applied in a bonding tool.Figure: Massive Diffusion Bonding The most common diffusion bonding process practicedin airframe structure manufacture is thin sheet diffusion bonding because of the large area bonds associated with thin sheet structures and the fact that the sheets are at Superplastic Forming (SPF) temperature. Wrought Udimet etc. it was detected a very thin film (10 to 40 µm) of two welded metals in the form of intermetallic phases. zirconium and beryllium metals and its alloy. MPW process is very fast. Nevertheless. Diffusion bonding is used to weld titanium. It can weld nickel alloy like Inconel. Magnetic pulse welding (MPW) is a joining process in which lap joint surfaces of cylindrical shape metals. Cu to Al etc. degradation of the electromechanical coupling factor and decreased efficiency occur. . It is used to weld dissimilar metals like Cu to Ti. in which melting and solidification processes took place. To avoid these difficulties.Figure: Thin sheet Diffusion Bonding DIFFUSION BONDING & MAGNETIC MATERIALS: Diffusion Bonding is an important manufacturing technique that can be used to manufacture some materials based on ceramics and magnetic materials that can be used as cores etc. MPW is classed in the group of solid-state bonding processes together with explosive welding (EXW). As a consequence. such as pipes and tubes. using electromagnetic forces. This leads to increased operating temperatures and possibly thermal runaway. OTHER APPLICATIONS: It is mostly used to weld refectory materials used in aerospace and nuclear industries. These in general have moduli an order of magnitude lower and loss factors an order of magnitude higher than the themselves. it has been necessary to use relatively thick to minimize the number of bonds. PiezoElectric stacks used have previously been bonded together using organic Methods. are welded by impact. produces no heat affected zone (HAZ) and may be performed without filler metals and protective gases. It can weld complex shapes. This process produces clean joint which is free from interface discontinuity and porosity. In many military aircraft diffusion bonding will help to allow for the conservation of expensive strategic materials and the reduction of manufacturing costs. in conjunction with superplastic forming. and often fabrication is mostly automated. temperature. some of the time interval could be accomplished in few minutes. Highly depend on welding parameters like surface finish. labor costs. It is simple in working. ADVANTAGES: The joint have same mechanical and physical properties as parent material. . beryllium. It is time consuming process. and nacelle frames. It does not use filler material. flux etc. Typical materials that are welded include titanium. diffusion bonding. This is often done using titanium or aluminum alloys for parts needed in the aerospace industry. However. Surface preparations of welding plates are more critical and difficult. due to different requirements. landing gear trunnions. So it is used to make precision components. is also used when creating complex sheet metal forms. DOWNSIDES/DISADVANTAGES: High initial or setup cost.Since this form of bonding takes a considerable amount of time compared to other joining techniques such as explosion welding. outboard and inboard actuator fittings. and part count. Size of the weld is limited according to equipment available. It takes more time compare to other welding process. Multiple sheets are stacked atop one another and bonded in specific sections. This process is not suitable for mass production. fuselages. including. pressure etc. which are used in arc welding process. and zirconium. parts are made in small quantities. It provides good dimension tolerance. In an attempt to reduce fastener count. Some aircraft have over 100 diffusion-bonded parts. welding material. Low running cost. The stack is then placed into a mold and gas pressure expands the sheets to fill the mold. Both similar and dissimilar material can be joint by diffusion bonding process. Nguyentat. https:/www. Arizona.REFERENCES: 1. 3. Edward D.wikipedia. 3.A. Welding handbook. ”Resistance And Solid State Welding And Other joining Processes”. 5 No. D..com 5. U. 1980. 4. “The Application of Superplastic Forming And Diffusion Bonding To Air Frame –Design And Manufacture”. Mantech Journal vol. 2000. 2.IBM General Products Division. Jakarta. E. International Symposium on Aeronautical Science And Technology Of Indonesia.Superplastic Forming / Diffusion Bonding.S.mech4study. Tucson.” Diffusion Bonding – An Advance Material Process For Aerospace Technology” Material Science Forum. Weisert. 3. Rigby . https:/www. Thinh.”Saving Up To 50% .. . Vol. 7th ed. 7.org/diffusion bonding 6. 1986. Stephen.