Effect of Texture and Grain Size on Bio-Corrosion Response of Ultrafine-Grained Titanium
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INTRODUCTION
FOR the past few decades, commercially pure titanium (CP-Ti) and titanium-based alloys have been used extensively for biomedical applications due to their excellent corrosion resistance, low modulus, superior biocompatibility, and osseointegration behavior in comparison to conventional biomedical alloys, such as type 316 stainless steel and cobalt chromium alloys.[1–3] The biocompatibility and corrosion resistance of titanium are the result of a passive TiO2 film of thickness 2 to 6 nm formed on the titanium surface.[4] Titanium alloy Ti-6Al4V is a well-studied material for orthopedic applications; however, the leaching of Al and V in due course of time results in toxicity and neurological disorders.[1] It has been noticed that the corrosion at the head-neck taper of the femoral component in metal on metal implants has led to severe corrosion and the leached ions have resulted in adverse tissue reactions.[5] Apart from corrosion, the failure of the Ti-6Al-4V implant due to poor fatigue strength, low wear resistance, high modulus of elasticity, and lack of osseointegration has also been clinically observed.[6–8] Thus, it is very essential to choose alloying N.P GURAO, formerly Ph.D. Student with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India, is now Assistant Professor with the Indian Institute of Technology, Kanpur, India. GEETHA MANIVASAGAM, Professor, is with the School of Mechanical and Building Sciences (SMBS), VIT University, Vellore 632014, India. Contact e-mail: [email protected] P. GOVINDARAJ, formerly Student with the School of Bio Sciences and Technology (SBST), VIT University, Vellore 632014, India, is now Assistant Professor with Alpha College of Engineering, Thirumazhisai, Chennai, India. R. ASOKAMANI, Professor, formerly with the School of Mechanical and Building Sciences (SMBS), VIT University, is now with the Dhanalakshmi College of Engineering, Dr. VPR Nagar, Thambaram, Chennai 601301, India. SATYAM SUWAS, Associate Professor, is with the Department of Materials Engineering, Indian Institute of Science. Manuscript submitted January 21, 2013. Article published online August 13, 2013 5602—VOLUME 44A, DECEMBER 2013
elements that will reduce the modulus of elasticity, enhance the hardness of the alloy, and minimize the toxic effects of the leached ions. An alternative option is to use unalloyed titanium with high strength and superior corrosion resistance. In order to improve the surface hardness and corrosion resistance of the unalloyed titanium, surface modification techniques like anodic oxidation treatment,[9] electrochemical treatment,[10] sandblasting,[11] carbide coatings,[12] laser nitriding,[13] electrolytic polishing,[14] etc., have been carried out. Recently, severe plastic deformation-based techniques have also been envisaged to improve the mechanical properties of titanium. Severe plastic deformation (SPD)-based processes lead to an ultrafine grain size (d ~ 100 to 1000 nm) in metallic materials contributing to superior grain size str
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