Effect of Thermal Cycling on Mechanical Properties of Pure Titanium Wire
Thong D. Ho
Department of Mechanical Engineering, College of Engineering, California State Polytechnic University Pomona, 3801 W Temple Avenue, Pomona, CA 91768, USA.
Yong X. Gan *
Department of Mechanical Engineering, College of Engineering, California State Polytechnic University Pomona, 3801 W Temple Avenue, Pomona, CA 91768, USA.
*Author to whom correspondence should be addressed.
Abstract
Pure titanium wire is attractive for corrosion-resistant, biomedical, and miniaturized structural applications because of its medium density, excellent corrosion resistance, biocompatibility, and favourable processability; however, its mechanical response is strongly influenced by grain size, texture, deformation mode, and oxygen uptake during thermal exposure. This study investigated the effect of air annealing on the room-temperature tensile behaviour of 26 AWG commercially pure Grade 1 titanium wire by comparing the as received condition with specimens annealed at 600°C for 2 h for one to six cycles and at 900°C for 2 h for one cycle. Load displacement data were converted to engineering and true stress–strain responses, and the tensile behaviour was evaluated in terms of yield behaviour, ultimate tensile response, elongation, and post-yield hardening characteristics. The as-received wire exhibited the most favourable overall tensile performance, showing the highest strength and greatest elongation, whereas all annealed conditions displayed reduced strength relative to the as-received material, with the greatest degradation in both strength and ductility observed after the 900°C exposure. Repeated 600°C exposures also altered the post yield flow and hardening response, indicating that thermal annealing changed the deformation behaviour of the wire in addition to lowering its strength. Optical microscopy further revealed clear surface discolouration after annealing, consistent with oxide layer development during thermal cycling in air. The results show that unprotected air annealing above 600°C is detrimental when retention of the original room-temperature tensile performance of Grade 1 titanium wire is required.
Keywords: Commercially pure titanium, grade 1 titanium wire, thermal cycling, air annealing, tensile strength, elongation, strain hardening, engineering stress–strain response, oxidation, optical microscopy