Papers by Keyword: Solid State Joining

Abstract: This study presents manufacturing lightweight aerospace components by solid state joining technologies. The advantages of solid state joining are due to the lack of hot cracking from solidification, since there is no liquid phase involved in joining process. This produces a high quality joint as compared to that from conventional fusion welding process. In diffusion bonding process, two different surfaces are matched together at elevated temperature under a low pressure without macroscopic plastic deformation in the interface. In friction stir welding process, the rotating shoulder of the tool generates frictional heat on the surface. As the pin rotates it forces the plastic material to mix mechanically in the vicinity of the pin and produces a heavily deformed microstructure around the pin. In this study, solid state joining processes of diffusion bonding and friction welding, are applied to manufacture several launcher components with lightweight, efficient and cost saving.

Abstract: This Paper presents the study on the weldability of two similar and two different metallic materials. The weldability of the similar metallic materials considered in the study were aluminum alloy pipes of grade AA6063. As for the weldability of two different metallic materials were aluminum alloy of grade AA6061 to low carbon steel of grade A36, dupl stainless steel of grade 2205 to low carbon steel of grade A36 and grey cast iron of grade A48 class 35 to low carbon steel BS 449 of grade 250. The differing methods of welding or joining processes are discussed herein including those of stir welding and hot pressed diffusion bonding of the similar and dissimilar metallic materials respectively as mentioned above. The weldability of between the two materials are investigated including the physical appearance of the joints and the strength integrity of those so far achieved at this stage. The paper also presented the results on the weldability of the similar and different metallic materials, recommendation for further in-depth study in pursuit for improved technologies on the subject matters and highlight the prospects of metallic materials welding or bonding or joining to fulfill the demands for different applications.

Abstract: Since solid state welding is formed from an intimate contact between two metals at temperatures below the melting point of the base materials, the structural integrity of welded zone is maintained without presence of foreign materials or temporary liquid phase. This paper provides some of examples for solid state joining of aerospace materials. Diffusion bonding process was developed for a titanium alloy for lightweight sandwich panels. Diffusion bonding of copper and stainless steel was also demonstrated to manufacture a combustion chamber. HIP (Hot Isostatic Press) bonding and friction stir welding process of aluminum alloy was developed in order to study possible application for a large launcher fuel tank. It is shown that solid state joining processes can be successfully applied to various aerospace materials and provide innovative solution for lightweight structures.

Abstract: In this study, the joint strength and microstructure of carbon steels welded by an super-deformation joining process in air were investigated. The two block of model steels are overlapped and heated. The steels are welded with 1000% deformation at approximately 1000°C.The joint strengths are evaluated by uniaxial tension testing. The joint microstructures and fractured surfaces are investigated with OM and SEM. The results revealed that the mechanical properties of joint are close to the matrix’s, the grains adjacent to the interface are merged into one grain, which indicates that both blocks are soundly joined,fracture surface was covered with dimple indicating ductile fracture occurred. Joint fracture behavior is initiated by the brittle fracture of scale inclusions and growth around the internal oxides. Surface scale is the most important factor of sound joining.

Abstract: FSW have advantage as defect such as porosity, metallic compounds decrease than other welding process. So, FSW was researched about low melting point materials. However, welding of high melting point and high strength materials attract attention because of high mechanical properties was needed due to industrial development. In this study, FSW is enforced using the kind of high melting point materials as SS400(SPHC). However, the tool must have super heat-resisting and abrasion resistance. So, WC-X%Co tool was manufactured by SPS method. The result, welding is successfully practice using WC-X%Co tool to 50m without fracture of tool.

Abstract: Inconel 738 (IN 738), like other precipitation-hardened nickel-base superalloys that contain a substantial amount of Al and Ti, is very difficult to weld due to its high susceptibility to heat-affected zone (HAZ) cracking during conventional fusion welding processes. The cause of this cracking, which is usually intergranular in nature, has been attributed to the liquation of various phases in the alloy, subsequent wetting of the grain boundaries by the liquid and decohesion across one of the solid-liquid interfaces due to on-cooling tensile stresses. In the present work, crack-free welding of the alloy was obtained by linear friction welding (LFW), notwithstanding the high susceptibility of the material to HAZ cracking. Gleeble thermomechanical simulation of the LFW process was carefully performed to study the microstructural response of IN 738 to the welding thermal cycle. Correlation between the simulated microstructure and that of the weldments was obtained, in that, a significant grain boundary liquation was observed in both the simulated specimens and actual weldments due to non-equilibrium reaction of second phase particles, including the strengthening gamma prime phase. These results show that in contrast to the general assumption of LFW being an exclusively solid-state joining process, intergranular liquation is possible during LFW. However, despite a significant occurrence of liquation in the alloy, no HAZ cracking was observed, which can be partly related to the nature of the imposed stress during LFW

Abstract: Solid State diffusion bonding is obtained by applying heat, well below the melting temperature of the metals, a static pressure which does not cause a macroscopic plastic deformation in the material, and a time required to form a metallurgical bond with atomic diffusion process. This process is used for aluminum alloys, high strength steels and titanium alloys in the aerospace industry to produce complex and inaccessible joints without localized distortion. Ability to diffusion bond titanium alloys is strongly needed to promote the use of superplastic forming technology. In the present work, the solid state diffusion bonding was carried out using specimens in Ti-6Al-4V and Ti-15V-3Cr-3Sn-3Al. The microstructure of the bonded interface indicates the diffusion bonding process is successful for both alloys. It is also shown that the diffusion bonding of a superplastic Ti-6Al-4V alloy is possible at the optimum superplastic condition so that two processes can be performed simultaneously. The structural integrity of diffusion bonding was evaluated with a hydraulic test of diffusion bonded part.