Enhanced superplasticity in commercially pure titanium alloy X.J. Zhu, M.J. Tan * , W. Zhou School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore Received 28 July 2004; received in revised form 17 November 2004; accepted 18 November 2004 Available online 16 December 2004 Abstract The superplasticity of commercially pure titanium alloy at high temperature was studied and the dynamic recrystallization phe- nomenon of the alloy was investigated by using electron back scattered diffraction. A two-step deformation method was used to increase the ductility of the alloy from 188% to 243%. Ó 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Titanium; Dynamic recrystallization; Superplasticity; Electron backscattering diffraction (EBSD) 1. Introduction Commercially pure (CP) titanium alloy, which shows excellent corrosion resistance and biocompatibility, is widely used in dental implants and prostheses [1,2]. Superplastic forming (SPF) is a cost-effective process for manufacturing complex shaped structural compo- nents [3–5] and SPF of commercially pure titanium alloy is very attractive for the biomedical industry due to the inert nature of this alloy. Unfortunately, studies on the SPF of CP titanium are limited. In the present study, the SPF and deformation behavior as well as related mechanism of CP titanium alloy is investigated. Kim et al. [6] have studied the hot deformation behavior of CP titanium alloy at high temperatures (750–950 °C) and pointed out that dynamic recrystalli- zation (DRX) can be observed at 750–850 °C. The posi- tive contributions of dynamic recrystallization on the superplasticity of Al–Mg alloys, Al 2219, Al 7475, Co 3 Ti and Mg–3Al–1Zn alloys have been well documented [7–13]. In the current paper, the DRX phenomenon of the CP titanium alloy during SPF and its effects on the superplasticity of this alloy is also investigated. 2. Experimental details Commercially pure titanium sheets of 1.5 mm thick- ness were used in this study. The chemical composition (wt%) of the present alloy was 0.01 C, 0.16 Fe, 0.008 N, 0.108 O, 0.0015 H and the balance was Ti. The average grain size of the as-received CP titanium alloy is 12.9 lm. Tensile specimens with a gauge of 15 mm length, 4 mm width and 1.5 mm thickness were electro- discharged machined with the tensile axis oriented paral- lel to the final rolling direction. The surfaces of the tensile sample gauge part were polished with silica paste. Uniaxial high temperature tensile tests were performed at 600 °C, 750 °C and 800 °C with different initial strain rates. All tests were conducted by first heating up each sample to the desired temperature, and this was followed by a 3 min holding time to ensure thermal equilibrium. After testing, the deformed specimens were cooled rap- idly to room temperature by forced cooling in order to preserve the microstructure. Specimens were sectioned from the gauge as well as grip regions. The samples were polished by silica paste and etched using 10%HF + 5%HNO 3 + 85%H 2 O for 5 s. For optical study, the lin- ear intercept procedure was employed for measuring the grain size. The electron back scattered diffraction (EBSD) measurements were carried out using a scan- 1359-6462/$ - see front matter Ó 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2004.11.017 * Corresponding author. Tel.: +6567905582; fax: +6567911859. E-mail address: mmjtan@ntu.edu.sg (M.J. Tan). www.actamat-journals.com Scripta Materialia 52 (2005) 651–655