The effect of strain rate on stress corrosion performance of Ti6Al4V alloy produced by additive manufacturing process

Abstract

Ti6Al4V alloy is considered as a favourable material for additive manufacturing (AM) and in particular for selective laser melting (SLM), due to the inherent difficulties relating to casting and plastic forming of this alloy. However, the significantly increased solidification rate associated with the SLM process results in a modified micro-structure and inherent casting imperfections that can have a detrimental effect on the alloy stress corrosion performance. The main objective of this study was to evaluate the effect of strain rate on stress corrosion behavior of Ti6Al4V alloy produced by SLM, as compared to its wrought alloy (Grade 5) counterpart of the same chemical composition. Micro-structure and phase identification were examined by scanning electron microscopy and X-ray diffraction analysis. General corrosion resistance was evaluated in terms of open circuit potential, potentiodynamic polarization analysis and by impedance spectroscopy, while stress corrosion behavior was examined at various strain rates in a 3.5% NaCl solution at ambient temperature. The results obtained revealed that general corrosion resistance and stress corrosion endurance at slow strain rate, in terms of time to failure and ductility of the SLM alloy, were relatively reduced, as compared to the wrought alloy counterpart. This was mainly due to the formation of a strained martensitic matrix in the form of α' phase and the significant reduction of the β phase in the alloy produced by SLM process.