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TIG Welding of Nickel Titanium to 304 Stainless Steel

Riggs, Mark R.

Abstract Details

2014, Master of Science, Ohio State University, Mechanical Engineering.
Nickel-titanium is a shape memory alloy capable of producing high stresses with an 8% maximum recoverable strain. The rotation of a nickel-titanium (NiTi) torque tube can be controlled by thermally cycling the material through its critical martensite and austenite temperatures. Transforming the phase of NiTi corresponds to a change in its crystalline structure and a macroscopic change in shape. This change in shape, through a controlled thermal input, lends itself well to powering a solid-state actuator. Shape memory alloys can in some cases replace traditional actuators, for instance in harsh aerospace environments where lightweight operation is critical. NiTi is effective as a solid-state actuator, but it is very difficult to machine. The poor machinability of NiTi drives the cost and complexity of system integration to the point where its widespread use is hindered. The general solution is to join NiTi to a structural material and machine the structural material for system integration. Several types of joining methods have been studied such as ultrasonic soldering, adhesives, and laser welding. This study focuses on tungsten inert gas (TIG) welded joints between 304 stainless steel and NiTi tubing. A nickel filler is used in TIG welding of NiTi to 304SS to prevent brittle intermetallics formed by titanium and iron in the weld pool. The thickness of the nickel filler and the current required to create a strong TIG weld in torsion failure is investigated in a Taguchi L9 full factorial test matrix. Based on ultimate failure torque test results and welding observations, a 0.050'' filler thickness with an 85 A starting current was chosen for thermocycling tests with a constant load. The chosen joint parameters produce an average ultimate failure torque of 371 in-lb (41.9 N-m) with a shear strength of 41 ksi (282 MPa). EDS analysis of 0.025'' and 0.075'' filler thickness welds confirm observations from welding and test data with a crack caused by TiFe intermetallics in the 0.025'' filler weld and minimal weld penetration on the 304SS interface with the 0.075'' filler thickness. Results from dye penetrant tests, ultimate failure test data, and sectioned weld analysis were used to gain understanding of TIG welding NiTi to 304SS.
Marcelo Dapino, Dr. (Advisor)
Mark Walter, Dr. (Committee Member)
104 p.

Recommended Citations

Citations

  • Riggs, M. R. (2014). TIG Welding of Nickel Titanium to 304 Stainless Steel [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397607979

    APA Style (7th edition)

  • Riggs, Mark. TIG Welding of Nickel Titanium to 304 Stainless Steel. 2014. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1397607979.

    MLA Style (8th edition)

  • Riggs, Mark. "TIG Welding of Nickel Titanium to 304 Stainless Steel." Master's thesis, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397607979

    Chicago Manual of Style (17th edition)