Effect of heat treatment on mechanical properties of bio-medical Ti-6A1-4V eli alloy

Balaji Devatha Venkatesh, Ryerson University

Date of Award

2008

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Mechanical Engineering

First Advisor

Daolun Chen

Second Advisor

Sanjeev Bhole

Abstract

Ti-6Al-4V alloy of extra low interstitial (ELI) grade has been used in biomedical applications because of its high strength-to-weight ratio and excellent biocompatibility. However, its poor wear resistance requires proper surface hardening. Body implants are also subjected to loads at varying strain rates. The objective to this study was to change the microstructure of Ti-6Al-4V ELI alloy via heat treatment and evaluate the mechanical properties with or without a hardened surface layer. It was observed that the hardened surface layer had only a small effect on the yield and tensile strengths but reduced ductility.

The strain hardening exponent decreased with increasing strain rate. The strain rate sensitivity decreased as the true strain increased. The fractal dimension of fracture surfaces was observed to be associated with the strength and ductility. Fatigue crack initiation was observed to occur at the specimen surface, regardless of the applied strain amplitudes and heat treatment conditions.