Study Of The Mechanical Performance Of Similar And Dissimilar Titanium Alloy Joints Formed By Diffusion Bonding And Friction Stir Welding

Titanium alloys have turned strategically important in aerospace applications due to their high strength to weight ratio, corrosion resistance, and good strength sustainability at high temperatures. The joining of lightweight materials such as titanium alloys in aerospace industries offer two main benefits of near net shape manufacturing and of reduction in buy to fly ratio. Among the various joining methods, Diffusion Bonding and Friction Stir Welding (FSW) can be combined with superplastic forming, therefore, have been widely accepted technique to join titanium alloys to produce complex sheet structures with reduced weight and fabrication costs compared to mechanically fastened structures. Both the processes are mainly optimized for titanium alloy, Ti-6Al-4V, to produce defect free sheets of it. The other titanium alloys such as Ti-6242 and Ti-54MFG offer advantages of high temperature sustainability and better machinability over Ti-6Al-4V. The joining of titanium alloys with different properties can improve the utilization of titanium alloys and increase the functional properties of joints. However, a very limited research has been conducted on joining techniques with dissimilar titanium alloys. Therefore, the current study examines the processes with dissimilar titanium alloys to broaden the application of the process with titanium alloys. The capability of diffusion bonding process for similar and dissimilar titanium alloys was studied with five titanium alloys, Ti-64SG, Ti-64FG, Ti-6242SG, Ti-54M, and Beta-21S, by maintaining two governing parameters pressure and time constant while the temperature was varied during the formation of joints. The friction stir welding of similar and dissimilar titanium joints was also studied with five titanium alloys, Ti-64SG,Ti-64FG,Ti-6242SG,Ti-6242FG, and Ti-54MFG, by varying two parameters namely, spindle speed and the feed rate, that control the quality of the process. The bond integrity of both the processes was evaluated with metallographic examination and mechanical testing. The surface and subsurface characteristics were examined to evaluate the surface characteristics and bonding strength. The mechanical strength of diffusion-bonded joints was investigated by conducting flexure testing whereas of the friction stir welded joints were examined by performing tensile tests. The probabilistic theoretical model of estimation of bonding time of dissimilar alloys was developed by computing the surface topography at the joint interface. A combined approach of numerical and experimental methodology was used to investigate the mechanical response of different titanium joints. The numerical model was developed to simulate flexural behavior of dissimilar diffusion bonded titanium joints from the material curves of its parent alloys. Similarly tensile behavior of friction stir welded similar titanium alloys for different process conditions was developed to identify the locations of maximum stress and strain in the joints. The numerical results were compared to experimentally determined behavior characteristics of the joints to gage the validity of the modeling approach. It was found that there was good agreement in the numerical and experimental results of the tensile behavior in titanium FSW joints. The diffusion bonding temperatures lower than the ß transus temperature of titanium alloys were identified to obtain sound bonds in similar and dissimilar titanium alloys. The quality of bonding was improved as the bonding temperature was increased. In case of friction stir welding, the optimum values of spindle speed and feed rate for the joints formed by similar titanium alloys were 275 RPM/100 mm min-1, whereas it was 325RPM/125 mm min-1 for the joints formed by dissimilar titanium alloys.

This book contains the papers from the Proceedings of the 1st international joint symposium on joining and welding held at Osaka University, Japan, 6-8 November 2013. The use of frictional heating to process and join materials has been used for many decades. Rotary and linear friction welding are vital techniques for many industrial sectors. More recently the development of friction stir welding (FSW) has significantly extended the application of friction processing. This conference is the first event organized by the three major institutes for joining and welding to focus on the broad range of friction processes. This symposium will provide the latest valuable information from academic and industrial experts from around the world on FSW, FSP, linear and rotary friction welding.

The combination of distinct materials is a key issue in modern industry, whereas the driving concept is to design parts with the right material in the right place. In this framework, a great deal of attention is directed towards dissimilar welding and joining technologies. In the automotive sector, for instance, the concept of “tailored blanks”, introduced in the last decade, has further highlighted the necessity to weld dissimilar materials. As far as the aeronautic field is concerned, most structures are built combining very different materials and alloys, in order to match lightweight and structural performance requirements. In this framework, the application of fusion welding techniques, namely, tungsten inert gas or laser welding, is quite challenging due to the difference in physical properties, in particular the melting point, between adjoining materials. On the other hand, solid-state welding methods, such as the friction stir welding as well as linear friction welding processes, have already proved to be capable of manufacturing sound Al-Cu, Al-Ti, Al-SS, and Al-Mg joints, to cite but a few. Recently, promising results have also been obtained using hybrid methods. Considering the novelty of the topic, many relevant issues are still open, and many research groups are continuously publishing valuable results. The aim of this book is to finalize the latest contributions on this topic.

This collection focuses on all aspects of science and technology related to friction stir welding and processing.

Materials Science and Engineering theme is a component of Encyclopedia of Physical Sciences, Engineering and Technology Resources in the global Encyclopedia of Life Support Systems (EOLSS), which is an integrated compendium of twenty one Encyclopedias. Materials Science and Engineering is concerned with the development and selection of the best possible material for a particular engineering task and the determination of the most effective method of producing the materials and the component. The Theme with contributions from distinguished experts in the field, discusses Materials Science and Engineering. In this theme the history of materials is traced and the concept of structure (atomic structure, microstructure and defect structure) and its relationship to properties developed. The theme is structured in five main topics: Materials Science and Engineering; Optimization of Materials Properties; Structural and Functional Materials; Materials Processing and Manufacturing Technologies; Detection of Defects and Assessment of Serviceability; Materials of the Future, which are then expanded into multiple subtopics, each as a chapter. These three volumes are aimed at the following five major target audiences: University and College students Educators, Professional practitioners, Research personnel and Policy analysts, managers, and decision makers and NGOs.

This report supplies information on joining processes applicable to titanium and its alloys in sheet metal applications, primarily related directly to airframe construction. Although the material presented here does not cover all titanium joining processes, and omits such processes as plasma-arc, submerged-arc, electroslag, flash, and high-frequency resistance welding, the data presented cover materials up to 2-inches thick in some cases and the report should be useful to anyone seeking titanium joining information. The joining processes covered fall into five categories: welding, brazing, metallurgical bonding (diffusion and deformation bonding), adhesive bonding, and mechanical fastening. The fusion welding processes that are discussed in detail include gas tungsten arc, gas metal arc, arc spot, and electron beam. The resistance processes give extended coverage are spot, roll spot, and seam welding. (Author).

This book includes recent theoretical and practical advancements in green composite materials and advanced manufacturing technology. It provides important original and theoretical experimental results which use nonroutine technologies often unfamiliar to some readers and covers novel applications of more familiar experimental techniques and analyses of composite problems. Green Materials and Advanced Manufacturing Technology: Concepts and Applications provides insight and a better understanding into the development of green composite materials and advanced manufacturing technology used in various manufacturing sectors. It highlights recent trends in the fields of green composites, metal matrix composites, ceramic matrix composites, surface modification using laser cladding, types of dust collectors in waste management and recycling in industries, machinability studies of metals and composites using surface grinding, drilling, electrical discharge machining, joining of metals using friction stir welding, shielded metal arc welding, and linear friction welding. This book is written for engineering students, postgraduate students, research scholars, faculty members, and industry professionals who are engaged in green composite materials and development of advanced manufacturing technology.

Collection of selected, peer reviewed papers from the 2013 International Conference on Mechanical, Automotive and Materials Engineering (CMAME 2013), July 26-27, 2013, Hong Kong. The 89 papers are grouped as follows: Chapter 1: Materials Science, Structural Composites, Materials Processing; Chapter 2: Nanomaterials Science; Chapter 3: Mechanical Properties of Materials, Deformation, Coating Engineering; Chapter 4: Computing Methods and Algorithms; Chapter 5: Experimental Methods and Studies; Chapter 6: Design, Modelling, Simulation and Optimization Technologies, CAD Applications; Chapter 7: Automation and Control, Detection and Tracking Technologies; Chapter 8: Advanced Technologies in Industry, Safety and Assessment.

Solid state joining of titanium via friction stir welding and diffusion bonding have emerged as enablers of efficient monolithic structural designs by the eliminations fasteners for the aerospace industry. As design complexity and service demands increase, the need for joints of dissimilar alloys has emerged. Complex thermomechanical conditions in friction stir weld joints and high temperature deformation behavior differences between alloys used in dissimilar joints gives rise to a highly variable flow pattern within a stir zone. Experiments performed welding Ti-6Al-4V to ß21S show that mechanical intermixing of the two alloys is the primary mechanism for the generation of the localized chemistry and microstructure, the magnitude of which can be directly related to pin rotation and travel speed weld parameters. Mechanical mixing of the two alloys is heavily influenced by strain rate softening phenomena, and can be used to manipulate weld nugget structure by switching which alloy is subjected to the advancing side of the pin. Turbulent mixing of a weld nugget and a significant reduction in defects and weld forces are observed when the ß21S is put on the advancing side of the weld where higher strain rates are present. Chemical diffusion driven by the heat of weld parameters is characterized using energy dispersive x-ray spectroscopy (EDS) and is shown to be a secondary process responsible for generating short-range chemical gradients that lead to a gradient of alpha particle structures. Diffusion calculations are inconsistent with an assumption of steady-state diffusion and show that material interfaces in the weld nugget evolve through the break-down of turbulent interface features generated by material flows. A high degree of recrystallization is seen throughout the welds, with unique, hybrid chemistry grains that are generated at material interfaces in the weld nugget that help to unify the crystal structure of dissimilar alloys. The degree of recrystallization is tied to the localized thermal profile in the weld nugget as well as the heating rates of a given set of weld parameters. Slow kinetics of alpha dissolution relative to the heating rate and process times of friction stir welding suggest an alpha-particle assisted super-transus recrystallization process contributes to a refined grain size in weld parameters utilizing high travel speed.

This book contains the Proceedings of the 13th World Conference on Titanium.