TRIBO-CORROSION BEHAVIOUR OF SEVERELY DEFORMED Ti6Al4V ALLOY

Abstract

Tribocorrosion (combined action of corrosion and wear) comes into picture in many places especially in orthopaedic implant materials. Orthopaedic implant materials are frequently subjected to fretting motions inside the body. The synergic action of fretting and corrosion in the presence of body fluid can lead to increased dissolution of metal ions into the body fluid which can catalyse further reactions causing infections, tissue inflammation, etc. ultimately leading to the failure of orthopaedic surgical operations. Ti6Al4V alloy is an excellent orthopaedic implant material. It has some very good properties like low density, high strength, high fatigue resistance, chemical inertness, low elastic modulus and excellent biocompatibility. However, it lacks in its wear properties. Hence, under fretting corrosion the material removal from this alloy can be expected to be substantially higher. The present study aims to address this issue through surface grain refinement. This is done through Ultrasonic shot peening (USP). Grain refinement improves the wear properties but its effect on corrosion resistance varies for different combinations of material and its environment. The ultra-fine grains (UFG) produced by USP is characterized through optical microscope, EBSD, micro-hardness and XRD. The corrosion resistance is investigated through the combined study of Tafel test, Electrochemical Impedance Spectroscopy (EIS) and X-Ray photoelectron spectroscopy (XPS). Further tribo-corrosion studies are also performed for studying the suitability of the processed alloy for tribological applications. The study provides an understanding on the effect of grain refinement produced by severe plastic deformation (SPD) on the tribological behaviour of the alloy.