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Impact Welding and Impulse Shape Calibration of Nickel and Titanium Alloys

Nirudhoddi, Bhuvi Swarna Lalitha
http://orcid.org/0000-0002-2784-7047
http://rave.ohiolink.edu/etdc/view?acc_num=osu1566161607171927

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
High-temperature metallic materials such as nickel-based and titanium alloys are attractive as skin structures for aerospace vehicles. They can allow significant performance improvement and mass reduction in aircraft. However, there are substantial challenges in welding and forming them affordably for service. This project examines the use of impulse-based methods, as enabled by the vaporizing foil actuator method, for the impact welding and precise shaping of alloys Ni - 718, Ni - 625, Ni - 230, and Ti 6242. The mechanical properties and weld microstructure of four similar and Six dissimilar VFA spot welding combinations are presented and analyzed. Microhardness measurements showed the absence of a heat affected zone (HAZ). The dissimilar Ni - Ni joints and Ni - Ti joints exhibited high loads to failure in lap-shear tests and show great potential for applications involving transition joints, repair welding, medical devices, and more. The VFA method is cheap, safe, fast, durable, and marks the advancement in the solid-state joining of dissimilar nickel and titanium systems. Nickel alloys typically exhibit low springback during quasi-static forming processes. However, the large amounts of strain hardening that occurs during these operations often requires a second annealing stress relief operation. Titanium alloys are commonly known to exhibit high springback levels due to the high strength to stiffness ratios of titanium alloys. Sheet metals components are usually shaped by hot or superplastic forming. This process is expensive and has long lead-times. This work examines an athermal process to relax or remove the residual stresses and elastic strains in sheet metals. All the materials explored, especially titanium showed significant improvements in shape conformance when processed through the VFA method. Recent shock-based calibration studies have provided some insight into the previously unconfirmed mechanism of springback relief. The driving hypothesis for this physical phenomenon is that modest shock waves plastically relieve elastic residual stresses and result in target shape conformance. To better understand this mechanism, VFA based shock processing experiments were used to change the curvature of pre-strained materials to a fully flat shape. It is speculated that the change in shape is a consequence of elastic stress relief caused by the propagation of planar shockwaves. A mechanics and shock physics based theory for shockwave interaction with residual stresses in a pre-strained sample is proposed. The possible pressures involved in this process were calculated from shock breakout velocity profiles captured by a photon doppler velocimetry system. The preliminary pressures are estimated to have satisfied the plastic yield criterion for this loading condition.
Glenn Daehn (Advisor)
Stephen Niezgoda (Committee Member)
Xun Liu (Committee Member)
177 p.
Engineering; Materials Science
impact welding; nickel to titanium; dissimilar welding; impulse; shockwave; calibration; springback; residual stress relief; athermal

Recommended Citations

Citations

  • Nirudhoddi, B. S. L. (2019). Impact Welding and Impulse Shape Calibration of Nickel and Titanium Alloys [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1566161607171927

    APA Style (7th edition)

  • Nirudhoddi, Bhuvi Swarna Lalitha. Impact Welding and Impulse Shape Calibration of Nickel and Titanium Alloys. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1566161607171927.

    MLA Style (8th edition)

  • Nirudhoddi, Bhuvi Swarna Lalitha. "Impact Welding and Impulse Shape Calibration of Nickel and Titanium Alloys." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1566161607171927

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.