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Metallurgical and Mechanical Characterization of High Temperature Titanium Alloys Joined by Friction Stir Welding.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Metallurgical and Mechanical Characterization of High Temperature Titanium Alloys Joined by Friction Stir Welding./
Author:	Gangwar, Kapil Dev.
Description:	1 online resource (721 pages)
Notes:	Source: Dissertation Abstracts International, Volume: 79-02(E), Section: B.
Subject:	Mechanical engineering. -
Online resource:	click for full text (PQDT)
ISBN:	9780355356205

Metallurgical and Mechanical Characterization of High Temperature Titanium Alloys Joined by Friction Stir Welding.
Gangwar, Kapil Dev.

Metallurgical and Mechanical Characterization of High Temperature Titanium Alloys Joined by Friction Stir Welding. - 1 online resource (721 pages)

Source: Dissertation Abstracts International, Volume: 79-02(E), Section: B.

Thesis (Ph.D.)--University of Washington, 2017.

Includes bibliographical references

In the world of joining, riveting and additive manufacturing, weight reduction, and omission of defects remain of paramount. Therefore, in the wake of ubiquitous fusion welding (FW) and widely accepted approach of riveting using Inconel bolts to resist corrosion at higher temperature, friction stir welding (FSW) has emerged as a novice jewel in friction based additive manufacturing industry. With advancements in automation of welding process and tool material, FSW of materials with higher work hardening such as steel and titanium has also become probable. Process and property relations associated with FSW are inevitable in case of dissimilar titanium alloys, due to presence of heterogeneity in and around the weld nugget. During FSW, a unique alpha + beta fine-grained microstructure has been formed depending on whether or not the peak temperature in the weld nugget (WN) reached above or below beta transus temperature. The resulting microstructure consists of acicular alpha + beta, emanating from the prior beta grain boundary as the weld cools off. The changes in the microstructure are observed by optical microscopy (OM). Later, a detailed analysis of material flow has been done by scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS). Hardness profiles on the transverse cross section of the weld have been measured in order to relate the deformation of main constituents, alpha {hexagonal close packed (hcp)}, and beta {body centered cubic (bcc)} that provides a new paradigm into grain refinement mechanism.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2018

Mode of access: World Wide Web

ISBN: 9780355356205Subjects--Topical Terms:

557493
Mechanical engineering.
Index Terms--Genre/Form:

554714
Electronic books.

Metallurgical and Mechanical Characterization of High Temperature Titanium Alloys Joined by Friction Stir Welding.
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245 1 0 $a Metallurgical and Mechanical Characterization of High Temperature Titanium Alloys Joined by Friction Stir Welding.
264 0 $c 2017
300 $a 1 online resource (721 pages)
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500 $a Source: Dissertation Abstracts International, Volume: 79-02(E), Section: B.
500 $a Adviser: Ramulu Mamidala.
502 $a Thesis (Ph.D.)--University of Washington, 2017.
504 $a Includes bibliographical references
520 $a In the world of joining, riveting and additive manufacturing, weight reduction, and omission of defects remain of paramount. Therefore, in the wake of ubiquitous fusion welding (FW) and widely accepted approach of riveting using Inconel bolts to resist corrosion at higher temperature, friction stir welding (FSW) has emerged as a novice jewel in friction based additive manufacturing industry. With advancements in automation of welding process and tool material, FSW of materials with higher work hardening such as steel and titanium has also become probable. Process and property relations associated with FSW are inevitable in case of dissimilar titanium alloys, due to presence of heterogeneity in and around the weld nugget. During FSW, a unique alpha + beta fine-grained microstructure has been formed depending on whether or not the peak temperature in the weld nugget (WN) reached above or below beta transus temperature. The resulting microstructure consists of acicular alpha + beta, emanating from the prior beta grain boundary as the weld cools off. The changes in the microstructure are observed by optical microscopy (OM). Later, a detailed analysis of material flow has been done by scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS). Hardness profiles on the transverse cross section of the weld have been measured in order to relate the deformation of main constituents, alpha {hexagonal close packed (hcp)}, and beta {body centered cubic (bcc)} that provides a new paradigm into grain refinement mechanism.
520 $a Material flow and evolving microstructure along with distribution of corresponding elements distribution was characterized by SEM, and EDS respectively. For the case of dissimilar alloys a necklace shaped macrostructure has been observed in the WN consisting of untransformed alpha migrating from the side of Ti-6242, and of basket-weave morphology of Ti-54M. Microhardness characterization undoubtedly reveals distinct boundaries between weld nugget and parent material. However, to understand the constitutive behavior of the thermo mechanically affected zone (TMAZ) on the advancing side (ADV), or retreating side (RET) and of WN, digital image correlation (DIC) technique has been adapted to develop strain maps in transverse tensile specimens. Improved mechanical properties of TMAZ on the ADV in comparison with RET TMAZ are in accordance with hardness values. Occurrence of fracture on the RET side, and morphology of the fractured surface have also been discussed. Based on the fractured morphology, it can be said that the presence of distinct and clustered island like morphologies in the form of transcrystalline and intercrystalline fracture is a results of microstructure that evolves due to difference in beta transus temperature of two alloys. The mechanical properties are analyzed and discussed in that regard.
520 $a Evolving volume fraction of phases along with their crystallographic orientation has also been elucidated. Evolution of texture has been discussed in terms of (100)alpha,(002)alpha,(110)beta ,(101)alpha and (102)alpha. Main constituents of texture in friction stir welded dissimilar titanium alloys, (101) alpha and (002)alpha have been discussed for their strength and orientation at various rotation speed. It has been highlighted that for the FSW of dissimilar titanium alloys (near alpha, and alpha + beta), center of the WN is stronger in texture in comparison with RET and ADV side. (Abstract shortened by ProQuest.).
520 $a Furthermore, state-of-the-art FSW technique has been used to weld dissimilar titanium alloys for post weld heat treatment (PWHT) studies at 933°C for 45 minutes. The processing parameters for welding are 225 rpm, and 125 mm-min -1. In light of recent PWHT, conducted for FSWed Ti-6Al-4V, in order to achieve super plasticity, our study focuses on dissimilar titanium alloys, Ti-54M, and Ti-6242 FG. A proper understanding of underlying material flow during FSW of dissimilar titanium alloys is essential in designing a monolithic structure operating under varying thermal and mechanical loading. Higher fraction of alpha with no pre-defined prior beta grain boundaries has been observed in PWHTed condition. Uniform, rather lower values of hardness have been achieved in the PWHTed specimen. Furthermore, Spatial arrangement, whether on ADV or RET, can significantly affect the evolution of microstructure, and congruent mechanical properties. In this study, Ti-54M and Ti-6242 FG have been joined by FSW with Ti-6242 FG being on ADV side. X-ray diffraction (XRD) technique has been utilized for phase evaluation, pole figure analysis, and residual stress measurements.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2018
538 $a Mode of access: World Wide Web
650 4 $a Mechanical engineering. $3 557493
650 4 $a Materials science. $3 557839
655 7 $a Electronic books. $2 local $3 554714
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690 $a 0794
710 2 $a ProQuest Information and Learning Co. $3 1178819
710 2 $a University of Washington. $b Mechanical Engineering. $3 1148544
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