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dc.contributor.supervisor Chaturvedi, M.C. (Mechanical and Manufacturing Engineering) Ojo, O.A. (Mechanical and Manufacturing Engineering) en
dc.contributor.author Ola, Oyedele Temitope
dc.date.accessioned 2011-01-19T16:34:19Z
dc.date.available 2011-01-19T16:34:19Z
dc.date.issued 2011-01-19T16:34:19Z
dc.identifier.uri http://hdl.handle.net/1993/4372
dc.description.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 along one of the solid-liquid interfaces due to on-cooling tensile stresses. To address the problem of liquation cracking in weldments, recent developments in welding research have resulted in supposedly exclusive solid-state friction joining processes, such as linear friction welding (LFW), for joining crack susceptible structural alloys. The objective of this work was therefore to investigate the weldability of the difficult-to-weld IN 738 superalloy by LFW and to analyze the resulting microstructural changes in the alloy due to the welding process. LFW was performed on Linear Friction Welding Process Development System (PDS) at the Aerospace Manufacturing Technology Centre of the Institute for Aerospace Research, National Research Council (NRC) of Canada. In order to study and decouple the effect of non-equilibrium thermal cycle and imposed compressive stress during the joining, physical simulation of the LFW process was performed by using Gleeble 1500-D Thermo-Mechanical Simulation System at the University of Manitoba. Detailed microstructural study of welded and Gleeble-simulated materials was carried out. 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, caused by non-equilibrium phase reaction(s), occurred during the process. However, despite a significant occurrence of liquation in the alloy, no HAZ cracking was observed. Nevertheless, the result showed that crack-free welding by linear friction welding is not due to preclusion of grain boundary liquation as has been commonly assumed and reported. Instead, resistance to cracking can be related to the counter-crack-formation effect of the imposed strain and to a concept observed and reported for the first time in this work, which is strain-induced rapid solidification. Furthermore, microstructural evolution during joining cannot be understood without considering the concept of non-equilibrium liquation reaction and strain-induced rapid solidification of the metastable liquid, which are carefully elucidated in this thesis. en
dc.format.extent 20049854 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US
dc.rights info:eu-repo/semantics/openAccess
dc.subject friction welding en
dc.subject Nickel base en
dc.subject heat affected zone en
dc.subject rapid solidification en
dc.subject strain-induced en
dc.subject liquid film migration en
dc.subject non-equilibrium dissolution en
dc.subject back diffusion en
dc.subject liquation reaction en
dc.subject compressive stress en
dc.title Microstructural Analysis of Linear Friction Welded Joint in Nickel-Base Inconel 738 Superalloy en
dc.type info:eu-repo/semantics/masterThesis
dc.degree.discipline Mechanical and Manufacturing Engineering en
dc.contributor.examiningcommittee Richards, N.L. (Mechanical and Manufacturing Engineering) Freund, M. (Chemistry) en
dc.degree.level Master of Science (M.Sc.) en
dc.description.note February 2011 en


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