Microstructural evolution in friction stir welding of Ti-6AI-4V
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| Language: | English |
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The Ohio State University / OhioLINK
2002
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=osu1407152313 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu1407152313 |
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oai_dc |
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NDLTD |
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English |
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NDLTD |
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Materials Science Engineering |
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Materials Science Engineering Karogal, Nikhil Uday Microstructural evolution in friction stir welding of Ti-6AI-4V |
| author |
Karogal, Nikhil Uday |
| author_facet |
Karogal, Nikhil Uday |
| author_sort |
Karogal, Nikhil Uday |
| title |
Microstructural evolution in friction stir welding of Ti-6AI-4V |
| title_short |
Microstructural evolution in friction stir welding of Ti-6AI-4V |
| title_full |
Microstructural evolution in friction stir welding of Ti-6AI-4V |
| title_fullStr |
Microstructural evolution in friction stir welding of Ti-6AI-4V |
| title_full_unstemmed |
Microstructural evolution in friction stir welding of Ti-6AI-4V |
| title_sort |
microstructural evolution in friction stir welding of ti-6ai-4v |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2002 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1407152313 |
| work_keys_str_mv |
AT karogalnikhiluday microstructuralevolutioninfrictionstirweldingofti6ai4v |
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1719436908229033984 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu14071523132021-08-03T06:26:42Z Microstructural evolution in friction stir welding of Ti-6AI-4V Karogal, Nikhil Uday Materials Science Engineering Friction stir welding (FSW) has been commercialized for certain applications of aluminum alloys. Ongoing research efforts are focusing on extending FSW to other high temperature materials such as steel, nickel alloys and titanium alloys. This study is a part of such an effort and looks into microstructural evolution in FSW of Ti-6A1-4V.Friction stir welds were produced in both mill annealed and ß annealed Ti-6A1-4V, followed by microstructural characterization, microhardness testing and texture analysis. Both the welds evaluated were interrupted welds, i.e. travel of the tool was stopped before the welding of the plates was complete. This facilitated the observation of micro structure around the point of tool removal. Microstructural characterization was done using SEM and texture analysis was done using OIM (Orientation Imaging Microscopy) technique. Residual stress analysis was conducted and compared to those in single pass fusion welds in Ti-6A1-4V.Macroscopic examination revealed a symmetric stir zone where the tool had completely stirred the material and a thermomechanically affected zone (TMAZ) was observed between the stir zone and the base material. Macroscopic examination of the longitudinal sections revealed that a region similar to the stir zone existed in a small region ahead of the weld, near the point of tool removal. The joint penetration in the welds was incomplete. The stir zone of both the welds consisted of colony a+ß in small prior ß grains (~10 µm) in size. The stir zone of the mill annealed welds also consisted of discretely scattered equiaxed a particles. The microstructures indicate that recrystallization occurred above the ß transus and the dwell time above the ß transus was short. The TMAZ of both the welds consisted of deformed base material and a "microstructurally distinct” band. A microstructurally distinct HAZ was not observed in either of the welds. Some grain growth was observed at the top of the weld due to the frictional heating from the shoulder of the tool. An increase in hardness was observed in the stir zone of both the welds that could be attributed to the small grain size in the stir zone. Microhardness observation in the longitudinal sections revealed that hardness remained uniform within the bulk of the SZ, although some reduction in hardness occurred at the top of the weld due to grain growth.Texture analysis revealed that the texture in the stir zone had changed due to recrystallization. The Burgers orientation relation between the a and ß phases was observed in the stir zone and indicating that the material was not deformed after the nucleation of the a phase. The randomness of the texture indicates that the cooling rate from the ß transus was relatively rapid. Some variant selection was also observed. Microtexture observation in the TMAZ revealed that the texture in the various regions of the TMAZ was different than either the base material or the stir zone. However, the deformed grains in the TMAZ of the mill annealed welds showed similar basal pole texture to the base material. This indicates some grain rotation mechanism about the basal poles in that region of the weld.The magnitude of residual stresses in friction stir welds was less than that in single pass fusion welding and the nature of stresses was also different. The level of cold work in the stir zone of the friction stir welds was very low due to recrystallization. Residual stress analysis was not possible in the multipass fusion welds due to the large grain size in the fusion zone.The fine grained micro structure and minimization of HAZ observed in the friction stir welds is highly desirable, compared to the coarse grained microstructure exhibited when fusion welding Ti-6A1-4V. The texture analysis provides valuable information about the deformation mechanism. The magnitude of residual stresses in FSW is less than that in single pass and multipass fusion welding. From a micro structure control standpoint, friction stir welding appears to be a promising welding technique for Ti-6A1-4V. 2002 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1407152313 http://rave.ohiolink.edu/etdc/view?acc_num=osu1407152313 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |